Sample records for early o-type stars
Fundamental Properties of O-Type Stars
Heap, Sara R.; Lanz, Thierry; Hubeny, Ivan
We present a comprehensive analysis of high-resolution, far-ultraviolet HST STIS, FUSE, and optical spectra of 18 O stars in the Small Magellanic Cloud. Our analysis is based on the OSTAR2002 grid of NLTE metal-line-blanketed model atmospheres calculated with our code TLUSTY. We systematically explore and present the sensitivity of various UV and optical lines to different stellar parameters. We have obtained consistent fits of the UV and the optical spectrum to derive the effective temperature, surface gravity, surface composition, and microturbulent velocity of each star. Stellar radii, masses, and luminosities follow directly. For stars of the same spectral subtype, we find a general good agreement between effective temperature determinations obtained with TLUSTY, CMFGEN, and FASTWIND models, which are all lower than the standard T(sub eff) calibration of O stars. We propose a new calibration between the spectral type and effective temperature based on our results from UV metal lines, as well as optical hydrogen and helium lines. The lower effective temperatures translate into ionizing luminosities that are smaller by a factor of 3 compared to luminosities inferred from previous standard calibrations. The chemical composition analysis reveals that the surface of about 80% of the program stars is moderately to strongly enriched in nitrogen, while showing the original helium, carbon, and oxygen abundances. Our results support the new stellar evolution models that predict that the surface of fast rotating stars becomes nitrogen-rich during the main-sequence phase because of rotationally induced mixing. Enrichment factors are, however, larger than predicted by stellar evolution models. Most stars exhibit the "mass discrepancy" problem, which we interpret as a result of fast rotation that lowers the measured effective gravity. Nitrogen enrichment and low spectroscopic masses are therefore two manifestations of fast rotation. Our study thus emphasizes the importance
Review: Magnetic Fields of O-Type Stars
Wade, G. A.; MiMeS Collaboration
Since 2002, strong, organized magnetic fields have been firmly detected at the surfaces of about 10 Galactic O-type stars. In this paper I will review the characteristics of the inferred fields of individual stars as well as the overall population. I will discuss the extension of the "magnetic desert,� first inferred among the A-type stars, to O stars up to 60 M⊙. I will discuss the interaction of the winds of the magnetic stars with the fields above their surfaces, generating complex "dynamical magnetosphere� structures detected in optical and UV lines, and in X-ray lines and continuum. Finally, I will discuss the detection of a small number of variable O stars in the LMC and SMC that exhibit spectral characteristics analogous to the known Galactic magnetic stars, and that almost certainly represent the first known examples of extragalactic magnetic stars.
The young stellar population of IC 1613. III. New O-type stars unveiled by GTC-OSIRIS
Garcia, M.; Herrero, A.
Context. Very low-metallicity massive stars are key to understanding the reionization epoch. Radiation-driven winds, chief agents in the evolution of massive stars, are consequently an important ingredient in our models of the early-Universe. Recent findings hint that the winds of massive stars with poorer metallicity than the SMC may be stronger than predicted by theory. Besides calling the paradigm of radiation-driven winds into question, this result would affect the calculated ionizing radiation and mechanical feedback of massive stars, as well as the role these objects play at different stages of the Universe. Aims: The field needs a systematic study of the winds of a large sample of very metal-poor massive stars. The sampling of spectral types is particularly poor in the very early types. This paper's goal is to increase the list of known O-type stars in the dwarf irregular galaxy IC 1613, whose metallicity is lower than the SMC's roughly by a factor 2. Methods: Using the reddening-free Q pseudo-colour, evolutionary masses, and GALEX photometry, we built a list of very likely O-type stars. We obtained low-resolution (R ~ 1000) GTC-OSIRIS spectra for a fraction of them and performed spectral classification, the only way to unequivocally confirm candidate OB-stars. Results: We have discovered 8 new O-type stars in IC 1613, increasing the list of 7 known O-type stars in this galaxy by a factor of 2. The best quality spectra were analysed with the model atmosphere code FASTWIND to derive stellar parameters. We present the first spectral type - effective temperature scale for O-stars beyond the SMC. Conclusions: The target selection method is successful. From the pre-selected list of 13 OB star candidates, we have found 8 new O-stars and 4 early-B stars and provided a similar type for a formerly known early-O star. Further tests are needed, but the presented procedure can eventually make preliminary low-resolution spectroscopy to confirm candidates unnecessary. The
The VLT-FLAMES Tarantula Survey. XII. Rotational velocities of the single O-type stars
Ramírez-Agudelo, O. H.; Simón-Díaz, S.; Sana, H.; de Koter, A.; Sabín-Sanjulían, C.; de Mink, S. E.; Dufton, P. L.; Gräfener, G.; Evans, C. J.; Herrero, A.; Langer, N.; Lennon, D. J.; Maíz Apellániz, J.; Markova, N.; Najarro, F.; Puls, J.; Taylor, W. D.; Vink, J. S.
Context. The 30 Doradus (30 Dor) region of the Large Magellanic Cloud, also known as the Tarantula nebula, is the nearest starburst region. It contains the richest population of massive stars in the Local Group, and it is thus the best possible laboratory to investigate open questions on the formation and evolution of massive stars. Aims: Using ground-based multi-object optical spectroscopy obtained in the framework of the VLT-FLAMES Tarantula Survey (VFTS), we aim to establish the (projected) rotational velocity distribution for a sample of 216 presumably single O-type stars in 30 Dor. The sample is large enough to obtain statistically significant information and to search for variations among subpopulations - in terms of spectral type, luminosity class, and spatial location - in the field of view. Methods: We measured projected rotational velocities, νesini, by means of a Fourier transform method and a profile fitting method applied to a set of isolated spectral lines. We also used an iterative deconvolution procedure to infer the probability density, P(νe), of the equatorial rotational velocity, νe. Results: The distribution of νesini shows a two-component structure: a peak around 80 kms-1 and a high-velocity tail extending up to ~600 kms-1. This structure is also present in the inferred distribution P(νe) with around 80% of the sample having 0 < νe ≤ 300 kms-1 and the other 20% distributed in the high-velocity region. The presence of the low-velocity peak is consistent with what has been found in other studies for late O- and early B-type stars. Conclusions: Most of the stars in our sample rotate with a rate less than 20% of their break-up velocity. For the bulk of the sample, mass loss in a stellar wind and/or envelope expansion is not efficient enough to significantly spin down these stars within the first few Myr of evolution. If massive-star formation results in stars rotating at birth with a large portion of their break-up velocities, an
Documentation for the machine-readable version of the catalog of galactic O type stars
Warren, W. H., Jr.
The Catalog of Galactic O-Type Stars (Garmany, Conti and Chiosi 1982), a compilation from the literature of all O-type stars for which spectral types, luminosity classes and UBV photometry exist, contains 765 stars, for each of which designation (HD, DM, etc.), spectral type, V, B-V, cluster membership, Galactic coordinates, and source references are given. Derived values of absolute visual and bolometric magnitudes, and distances are included. The source reference should be consulted for additional details concerning the derived quantities. This description of the machine-readable version of the catalog seeks to enable users to read and process the data with a minimum of guesswork. A copy of this document should be distributed with any machine readable version of the catalog.
A radial velocity survey of the Carina Nebula's O-type stars
Kiminki, Megan M.; Smith, Nathan
We have obtained multi-epoch observations of 31 O-type stars in the Carina Nebula using the CHIRON spectrograph on the CTIO/SMARTS 1.5-m telescope. We measure their radial velocities to 1-2 km s-1 precision and present new or updated orbital solutions for the binary systems HD 92607, HD 93576, HDE 303312, and HDE 305536. We also compile radial velocities from the literature for 32 additional O-type and evolved massive stars in the region. The combined data set shows a mean heliocentric radial velocity of 0.6 km s-1. We calculate a velocity dispersion of ≤9.1 km s-1, consistent with an unbound, substructured OB association. The Tr 14 cluster shows a marginally significant 5 km s-1 radial velocity offset from its neighbour Tr 16, but there are otherwise no correlations between stellar position and velocity. The O-type stars in Cr 228 and the South Pillars region have a lower velocity dispersion than the region as a whole, supporting a model of distributed massive star formation rather than migration from the central clusters. We compare our stellar velocities to the Carina Nebula's molecular gas and find that Tr 14 shows a close kinematic association with the Northern Cloud. In contrast, Tr 16 has accelerated the Southern Cloud by 10-15 km s-1, possibly triggering further massive star formation. The expansion of the surrounding H II region is not symmetric about the O-type stars in radial velocity space, indicating that the ionized gas is constrained by denser material on the far side.
Mass loss in O-type stars - Parameters which affect it
Garmany, C. D.; Conti, P. S.
Newly determined mass loss rates are presented for sixteen O-type stars in three open clusters. Combining the data with that already in the literature, no evidence is found that the rates are different in clusters with differing galactocentric distances and compositions, at least near the sun. There is still appreciable dispersion in the relationship between the mass loss rate and the stellar luminosity. It may be that the mass loss depends additionally on the stellar mass and/or radius, but these data cannot unequivocally indicate which physical dependence is correct. Evidence is found that a stellar wind increases as a massive star evolves from the zero-age main sequence.
The MiMeS survey of Magnetism in Massive Stars: magnetic analysis of the O-type stars
Grunhut, J. H.; Wade, G. A.; Neiner, C.; Oksala, M. E.; Petit, V.; Alecian, E.; Bohlender, D. A.; Bouret, J.-C.; Henrichs, H. F.; Hussain, G. A. J.; Kochukhov, O.; MiMeS Collaboration
We present the analysis performed on spectropolarimetric data of 97 O-type targets included in the framework of the Magnetism in Massive Stars (MiMeS) Survey. Mean least-squares deconvolved Stokes I and V line profiles were extracted for each observation, from which we measured the radial velocity, rotational and non-rotational broadening velocities, and longitudinal magnetic field Bℓ. The investigation of the Stokes I profiles led to the discovery of two new multiline spectroscopic systems (HD 46106, HD 204827) and confirmed the presence of a suspected companion in HD 37041. We present a modified strategy of the least-squares deconvolution technique aimed at optimizing the detection of magnetic signatures while minimizing the detection of spurious signatures in Stokes V. Using this analysis, we confirm the detection of a magnetic field in six targets previously reported as magnetic by the MiMeS collaboration (HD 108, HD 47129A2, HD 57682, HD 148937, CPD-28 2561, and NGC 1624-2), as well as report the presence of signal in Stokes V in three new magnetic candidates (HD 36486, HD 162978, and HD 199579). Overall, we find a magnetic incidence rate of 7 ± 3 per cent, for 108 individual O stars (including all O-type components part of multiline systems), with a median uncertainty of the Bℓ measurements of about 50 G. An inspection of the data reveals no obvious biases affecting the incidence rate or the preference for detecting magnetic signatures in the magnetic stars. Similar to A- and B-type stars, we find no link between the stars' physical properties (e.g. Teff, mass, and age) and the presence of a magnetic field. However, the Of?p stars represent a distinct class of magnetic O-type stars.
A search for spectroscopic binaries among the runaway O type stars
Stone, R. C.
Numerous radial velocity measurements of medium dispersion were made for the 10 brighter stars given in Stone's list of very probable O type runaways. All plates were measured with the KPNO PDS microdensitometer, and a new iterative reductional analysis was used to derive plate velocities, which are estimated to be 1.6 times more accurate internally than those found by using the traditional method. Of thse stars, psi Per, alpha Cam, HD 188209, and 26 Cep are identified as probable velocity variables, while 9 Sge, lambda Cep, and HD 218915 are classed as possible variables. If the source of this variability is Keplerian rather than atmospheric, which cannot be established unequivocally from the observations of this paper, psi Per could be a spectroscopic binary with a black hole companion, and at least 1.2 solar mass. The detection of runaway binary systems from radial velocity measurements is discussed.
A KEPLERIAN-LIKE DISK AROUND THE FORMING O-TYPE STAR AFGL 4176
Johnston, Katharine G.; Hoare, Melvin G.; Robitaille, Thomas P.
We present Atacama Large Millimeter/submillimeter Array line and continuum observations at 1.2 mm with ∼0.″3 resolution that uncover a Keplerian-like disk around the forming O-type star AFGL 4176. The continuum emission from the disk at 1.21 mm (source mm1) has a deconvolved size of 870 ± 110 AU × 330 ± 300 AU and arises from a structure ∼8 M{sub ⊙} in mass, calculated assuming a dust temperature of 190 K. The first-moment maps, pixel-to-pixel line modeling, assuming local thermodynamic equilibrium (LTE), and position–velocity diagrams of the CH{sub 3}CN J = 13–12 K-line emission all show a velocity gradient alongmore » the major axis of the source, coupled with an increase in velocity at small radii, consistent with Keplerian-like rotation. The LTE line modeling shows that where CH{sub 3}CN J = 13–12 is excited, the temperatures in the disk range from ∼70 to at least 300 K and that the H{sub 2} column density peaks at 2.8 × 10{sup 24} cm{sup −2}. In addition, we present Atacama Pathfinder Experiment {sup 12}CO observations that show a large-scale outflow from AFGL 4176 perpendicular to the major axis of mm1, supporting the disk interpretation. Finally, we present a radiative transfer model of a Keplerian disk surrounding an O7 star, with a disk mass and radius of 12 M{sub ⊙} and 2000 AU that reproduces the line and continuum data, further supporting our conclusion that our observations have uncovered a Keplerian-like disk around an O-type star.« less
Chasing discs around O-type (proto)stars: Evidence from ALMA observations
Cesaroni, R.; Sánchez-Monge, �.; Beltrán, M. T.; Johnston, K. G.; Maud, L. T.; Moscadelli, L.; Mottram, J. C.; Ahmadi, A.; Allen, V.; Beuther, H.; Csengeri, T.; Etoka, S.; Fuller, G. A.; Galli, D.; Galván-Madrid, R.; Goddi, C.; Henning, T.; Hoare, M. G.; Klaassen, P. D.; Kuiper, R.; Kumar, M. S. N.; Lumsden, S.; Peters, T.; Rivilla, V. M.; Schilke, P.; Testi, L.; van der Tak, F.; Vig, S.; Walmsley, C. M.; Zinnecker, H.
Context. Circumstellar discs around massive stars could mediate the accretion onto the star from the infalling envelope, and could minimize the effects of radiation pressure. Despite such a crucial role, only a few convincing candidates have been provided for discs around deeply embedded O-type (proto)stars. Aims: In order to establish whether disc-mediated accretion is the formation mechanism for the most massive stars, we have searched for circumstellar, rotating discs around a limited sample of six luminous (>105L⊙) young stellar objects. These objects were selected on the basis of their IR and radio properties in order to maximize the likelihood of association with disc+jet systems. Methods: We used ALMA with 0.̋2 resolution to observe a large number of molecular lines typical of hot molecular cores. In this paper we limit our analysis to two disc tracers (methyl cyanide, CH3CN, and its isotopologue, 13CH3CN), and an outflow tracer (silicon monoxide, SiO). Results: We reveal many cores, although their number depends dramatically on the target. We focus on the cores that present prominent molecular line emission. In six of these a velocity gradient is seen across the core,three of which show evidence of Keplerian-like rotation. The SiO data reveal clear but poorly collimated bipolar outflow signatures towards two objects only. This can be explained if real jets are rare (perhaps short-lived) in very massive objects and/or if stellar multiplicity significantly affects the outflow structure.For all cores with velocity gradients, the velocity field is analysed through position-velocity plots to establish whether the gas is undergoing rotation with νrot � R- α, as expected for Keplerian-like discs. Conclusions: Our results suggest that in three objects we are observing rotation in circumstellar discs, with three more tentative cases, and one core where no evidence for rotation is found. In all cases but one, we find that the gas mass is less than the mass of
The VLT-FLAMES Tarantula Survey. VIII. Multiplicity properties of the O-type star population
Sana, H.; de Koter, A.; de Mink, S. E.; Dunstall, P. R.; Evans, C. J.; Hénault-Brunet, V.; Maíz Apellániz, J.; Ramírez-Agudelo, O. H.; Taylor, W. D.; Walborn, N. R.; Clark, J. S.; Crowther, P. A.; Herrero, A.; Gieles, M.; Langer, N.; Lennon, D. J.; Vink, J. S.
Context. The Tarantula Nebula in the Large Magellanic Cloud is our closest view of a starburst region and is the ideal environment to investigate important questions regarding the formation, evolution and final fate of the most massive stars. Aims: We analyze the multiplicity properties of the massive O-type star population observed through multi-epoch spectroscopy in the framework of the VLT-FLAMES Tarantula Survey. With 360 O-type stars, this is the largest homogeneous sample of massive stars analyzed to date. Methods: We use multi-epoch spectroscopy and variability analysis to identify spectroscopic binaries. We also use a Monte-Carlo method to correct for observational biases. By modeling simultaneously the observed binary fraction, the distributions of the amplitudes of the radial velocity variations and the distribution of the time scales of these variations, we constrain the intrinsic current binary fraction and period and mass-ratio distributions. Results: We observe a spectroscopic binary fraction of 0.35 ± 0.03, which corresponds to the fraction of objects displaying statistically significant radial velocity variations with an amplitude of at least 20 km s-1. We compute the intrinsic binary fraction to be 0.51 ± 0.04. We adopt power-laws to describe the intrinsic period and mass-ratio distributions: f(log 10P/d) ~ (log 10P/d)π (with log 10P/d in the range 0.15-3.5) and f(q) ~ qκ with 0.1 ≤ q = M2/M1 ≤ 1.0. The power-law indexes that best reproduce the observed quantities are π = -0.45 ± 0.30 and κ = -1.0 ± 0.4. The period distribution that we obtain thus favours shorter period systems compared to an Öpik law (π = 0). The mass ratio distribution is slightly skewed towards low mass ratio systems but remains incompatible with a random sampling of a classical mass function (κ = -2.35). The binary fraction seems mostly uniform across the field of view and independent of the spectral types and luminosity classes. The binary fraction in the outer
The Physical Properties and Effective Temperature Scale of O-Type Stars as a Function of Metallicity. I. A Sample of 20 Stars in the Magellanic Clouds
Massey, Philip; Bresolin, Fabio; Kudritzki, Rolf P.; Puls, Joachim; Pauldrach, A. W. A.
We have obtained Hubble Space Telescope (HST) and ground-based observations of a sample of 20 O-type stars in the LMC and SMC, including six of the hottest massive stars known (subtypes O2-O3) in the R136 cluster. In general, these data include (1) the HST UV spectra in order to measure the terminal velocities of the stellar winds, (2) high signal-to-noise, blue-optical data where the primary temperature- and gravity-sensitive photospheric lines are found, and (3) nebular-free Hα profiles, which provide the mass-loss rates. We find that the older (Faint Object Spectrograph) HST data of the R136 stars (which were obtained without the benefits of sky measurements) suffered from significant nebular emission, which would increase the derived mass-loss rates by factors of ~3, all other factors being equal. We also find several stars in the SMC for which the N III λλ4634, 4642 and He II λ4686 emission ``f'' characteristics do not appear to follow the same pattern as in Galactic stars. Since He II emission is due to the stellar wind (which will be weaker in SMC for stars of the same luminosity), while N III emission is a complex non-LTE (NLTE) effect affected mostly by temperature, it would not be surprising to find that these features do not correlate with each other or with luminosity in SMC stars in the same was as they do in Galactic stars, but theory does not provide a clean answer, and analysis of more stars (both SMC and Galactic) is needed to resolve this issue. The line-blanketed NLTE atmosphere code FASTWIND was then used to determine the physical parameters of this sample of stars. We find good agreement between the synthetic line profiles for the hydrogen, He I, and He II lines in the majority of the stars we analyzed; the three exceptions show evidence of being incipiently resolved spectroscopic binaries or otherwise spectral composites. One such system is apparently an O3 V+O3 V eclipsing binary, and a follow-up radial velocity study is planned to obtain
Relationship between optical and X-ray properties of O-type stars surveyed with the Einstein Observatory
Sciortino, S.; Vaiana, G. S.; Harnden, F. R., Jr.; Ramella, M.; Morossi, C.
An X-ray luminosity function is derived for a representative volume-limited sample of O-type stars selected from the catalog of Galactic O stars surveyed with the Einstein Observatory. It was found that, for the stars of this sample which is ten times larger than any previously analyzed, the level of X-ray emission is strongly correlated with bolometric luminosity, confirming previous findings of an Lx-L(bol) relationship (e.g., Harnden et al., 1979; Pallavicini et al., 1981). Correlations between the Lx and the mass loss rate with the wind terminal velocity or with the rotation rate were weak. However, there was a strong correlation with wind momentum flux as well as with the wind kinetic energy flux.
A Detailed Far-ultraviolet Spectral Atlas of O-type Stars
Smith, Myron A.
In this paper, we present a spectral atlas covering the wavelength interval 930-1188 Ã… for O2-O9.5 stars using Far-Ultraviolet Spectroscopic Explorer archival data. The stars selected for the atlas were drawn from three populations: Galactic main-sequence (classes III-V) stars, supergiants, and main-sequence stars in the Magellanic Clouds, which have low metallicities. For several of these stars, we have prepared FITS files comprised of pairs of merged spectra for user access via the Multimission Archive at Space Telescope (MAST). We chose spectra from the first population with spectral types O4, O5, O6, O7, O8, and O9.5 and used them to compile tables and figures with identifications of all possible atmospheric and interstellar medium lines in the region 949-1188 Ã…. Our identified line totals for these six representative spectra are 821 (500), 992 (663), 1077 (749), 1178 (847), 1359 (1001), and 1798 (1392) lines, respectively, where the numbers in parentheses are the totals of lines formed in the atmospheres, according to spectral synthesis models. The total number of unique atmospheric identifications for the six main-sequence O-star template spectra is 1792, whereas the number of atmospheric lines in common to these spectra is 300. The number of identified lines decreases toward earlier types (increasing effective temperature), while the percentages of "missed" features (unknown lines not predicted from our spectral syntheses) drop from a high of 8% at type B0.2, from our recently published B-star far-UV atlas, to 1%-3% for type O spectra. The percentages of overpredicted lines are similar, despite their being much higher for B-star spectra. We discuss the statistics of line populations among the various elemental ionization states. Also, as an aid to users we list those isolated lines that can be used to determine stellar temperatures and the presence of possible chemical anomalies. Finally, we have prepared FITS files that give pairs of merged spectra for
Spectroscopic and physical parameters of Galactic O-type stars. III. Mass discrepancy and rotational mixing
Markova, N.; Puls, J.; Langer, N.
Context. Massive stars play a key role in the evolution of galaxies and our Universe. Aims: Our goal is to compare observed and predicted properties of single Galactic O stars to identify and constrain uncertain physical parameters and processes in stellar evolution and atmosphere models. Methods: We used a sample of 53 objects of all luminosity classes and with spectral types from O3 to O9.7. For 30 of these, we determined the main photospheric and wind parameters, including projected rotational rates accounting for macroturbulence, and He and N surface abundances, using optical spectroscopy and applying the model atmosphere code FASTWIND. For the remaining objects, similar data from the literature, based on analyses by means of the CMFGEN code, were used instead. The properties of our sample were then compared to published predictions based on two grids of single massive star evolution models that include rotationally induced mixing. Results: Any of the considered model grids face problem in simultaneously reproducing the stellar masses, equatorial gravities, surface abundances, and rotation rates of our sample stars. The spectroscopic masses derived for objects below 30 M⊙ tend to be smaller than the evolutionary ones, no matter which of the two grids have been used as a reference. While this result may indicate the need to improve the model atmosphere calculations (e.g. regarding the treatment of turbulent pressure), our analysis shows that the established mass problem cannot be fully explained in terms of inaccurate parameters obtained by quantitative spectroscopy or inadequate model values of Vrot on the zero age main sequence. Within each luminosity class, we find a close correlation of N surface abundance and luminosity, and a stronger N enrichment in more massive and evolved O stars. Additionally, we also find a correlation of the surface nitrogen and helium abundances. The large number of nitrogen-enriched stars above 30 M⊙ argues for rotationally
A spectroscopic search for colliding stellar winds in O-type close binary systems. II - Plaskett's star (HD 47129)
Wiggs, Michael S.; Gies, Douglas R.
New evidence for colliding winds in the massive O-type binary system Plaskett's star is reported. High S/N ratio spectra of the H-alpha and He I 6678 emission lines are presented, and their orbital phase-related variations are examined in order to derive the locations and motions of the high-density gas in the system. Radial velocity cures for several absorption and emission lines associated with the photosphere of the primary are also provided. The H-alpha emission profiles are complex, with very broad wings and a sharp spikelike feature that approximately follows the motion of the primary star. The radial velocity curve for this spike lags behind the photospheric velocity curve of the primary by 0.066 in phase. It is suggested that the high-velocity H-alpha emission is related to instabilities in the intershock region between the two component stars. The H-alpha phase-related variations are compared with those observed in the UV wind lines in IUE archival spectra.
Quantitative spectroscopic analyses in the IACOB+OWN project: Massive O-type stars in the Galaxy with the current Gaia information
Holgado, Gonzalo; Simón-Díaz, Sergio; Barbá, Rodolfo
We present the results from the quantitative spectroscopic analysis of ~280 likely single O stars targeted by the IACOB and OWN surveys. This implies the largest sample of Galactic O-type stars analyzed homogeneously to date. We used the iacob-broad and iacob-gbat tools (see Simón-Díaz et al. 2011,2015) to obtain the complete set of spectroscopic parameters which can be determined from the optical spectrum of O-type stars: projected rotational velocity (v sin i), macroturbulence velocity (v mac), effective temperature (T eff), gravity (logg), wind-strength (logQ), helium abundance (Y He), microturbulence (ξt), and the exponent of the wind-law (β).
Macroclumping as solution of the discrepancy between Hα and P v mass loss diagnostics for O-type stars
Šurlan, B.; Hamann, W.-R.; Aret, A.; Kubát, J.; Oskinova, L. M.; Torres, A. F.
Context. Recent studies of O-type stars have demonstrated that discrepant mass-loss rates are obtained when different diagnostic methods are employed. Fitting the unsaturated UV resonance lines (e.g., P v) gives drastically lower values than obtained from the Hα emission. Wind inhomogeneity (so-called "clumping") may be the main cause of this discrepancy. Aims: In a previous paper, we presented 3D Monte-Carlo calculations for the formation of scattering lines in a clumped stellar wind. In the present paper we select five O-type supergiants (from O4 to O7) and test whether the reported discrepancies can be resolved this way. Methods: In the first step, the analyses started with simulating the observed spectra with Potsdam Wolf-Rayet (PoWR) non-LTE model atmospheres. The mass-loss rates are adjusted to fit to the observed Hα emission lines best. For the unsaturated UV resonance lines (i.e., P v) we then applied our 3D Monte-Carlo code, which can account for wind clumps of any optical depths ("macroclumping"), a non-void interclump medium, and a velocity dispersion inside the clumps. The ionization stratifications and underlying photospheric spectra were adopted from the PoWR models. The properties of the wind clumps were constrained by fitting the observed resonance line profiles. Results: Our results show that with the mass-loss rates that fit Hα (and other Balmer and He ii lines), the UV resonance lines (especially the unsaturated doublet of P v) can also be reproduced with no problem when macroclumping is taken into account. There is no need to artificially reduce the mass-loss rates or to assume a subsolar phosphorus abundance or an extremely high clumping factor, unlike what was claimed by other authors. These consistent mass-loss rates are lower by a factor of 1.3 to 2.6, compared to the mass-loss rate recipe from Vink et al. Conclusions: Macroclumping resolves the previously reported discrepancy between Hα and P v mass-loss diagnostics. Based on
The Development of STAR Early Literacy. Report.
School Renaissance Inst., Inc., Madison, WI.
This report describes the development and testing of a computerized early literacy diagnostic assessment for students in prekindergarten to grade 3 that can measure skills across a variety of preliteracy and reading domains. The STAR Early Literacy assessment was developed by a team of more than 50 people, including literacy experts,…
The IACOB project. V. Spectroscopic parameters of the O-type stars in the modern grid of standards for spectral classification
Holgado, G.; Simón-Díaz, S.; Barbá, R. H.; Puls, J.; Herrero, A.; Castro, N.; Garcia, M.; Maíz Apellániz, J.; Negueruela, I.; Sabín-Sanjulián, C.
Context. The IACOB and OWN surveys are two ambitious, complementary observational projects which have made available a large multi-epoch spectroscopic database of optical high resolution spectra of Galactic massive O-type stars. Aims: Our aim is to study the full sample of (more than 350) O stars surveyed by the IACOB and OWN projects. As a first step towards this aim, we have performed the quantitative spectroscopic analysis of a subsample of 128 stars included in the modern grid of O-type standards for spectral classification. The sample comprises stars with spectral types in the range O3-O9.7 and covers all luminosity classes. Methods: We used the semi-automatized IACOB-BROAD and IACOB-GBAT/FASTWIND tools to determine the complete set of spectroscopic parameters that can be obtained from the optical spectrum of O-type stars. A quality flag was assigned to the outcome of the IACOB-GBAT/FASTWIND analysis for each star, based on a visual evaluation of how the synthetic spectrum of the best fitting FASTWIND model reproduces the observed spectrum. We also benefitted from the multi-epoch character of the IACOB and OWN surveys to perform a spectroscopic variability study of the complete sample, providing two different flags for each star accounting for spectroscopic binarity as well as variability of the main wind diagnostic lines. Results: We obtain - for the first time in a homogeneous and complete manner - the full set of spectroscopic parameters of the "anchors" of the spectral classification system in the O star domain. We provide a general overview of the stellar and wind parameters of this reference sample, as well as updated recipes for the SpT-Teff and SpT-log g calibrations for Galactic O-type stars. We also propose a distance-independent test for the wind-momentum luminosity relationship. We evaluate the reliability of our semi-automatized analysis strategy using a subsample of 40 stars extensively studied in the literature, and find a fairly good agreement
Hot ammonia around young O-type stars. III. High-mass star formation and hot core activity in W51 Main
Goddi, C.; Ginsburg, A.; Zhang, Q.
Context. This paper is the third in a series of NH3 multilevel imaging studies in well-known, high-mass star-forming regions. The main goal is to characterize kinematics and physical conditions of (hot and dense) circumstellar molecular gas around O-type young stars. Aims: We want to map at subarcsecond resolution highly excited inversion lines of NH3 in the high-mass star-forming region W51 Main (distance = 5.4 kpc), which is an ideal target to constrain theoretical models of high-mass star formation. Methods: Using the Karl Jansky Very Large Array (JVLA), we mapped the hot and dense molecular gas in W51 Main with ~0.2 arcsec-0.3 arcsec angular resolution in five metastable (J = K) inversion transitions of ammonia (NH3): (J,K) = (6, 6), (7, 7), (9, 9), (10, 10), and (13, 13). These lines arise from energy levels between ~400 K and ~1700 K above the ground state. We also made maps of the (free-free) continuum emission at frequencies between 25 and 36 GHz. Results: We have identified and characterized two main centers of high-mass star formation in W51 Main, which excite hot cores and host one or multiple high-mass young stellar objects (YSOs) at their centers: the W51e2 complex and the W51e8 core (~6'' southward of W51e2). The former breaks down into three further subcores: W51e2-W, which surrounds the well-known hypercompact (HC) HII region, where hot NH3 is observed in absorption, and two additional dusty cores, W51e2-E (~0.8 arcsec to the East) and W51e2-NW (~1'' to the North), where hot NH3 is observed in emission. The velocity maps toward the HC HII region show a clear velocity gradient along the east-west in all lines. The gradient may indicate rotation, although any Keplerian motion must be on smaller scales (<1000 AU) as we do not directly observe a Keplerian velocity profile. The absence of outflow and/or maser activity and the low amount of molecular gas available for accretion (~5 M⊙, assuming [NH3]/[H2] = 10-7) with respect to the mass of the central
VizieR Online Data Catalog: Far-UV spectral atlas of O-type stars (Smith, 2012)
Smith, M. A.
In this paper, we present a spectral atlas covering the wavelength interval 930-1188Ã… for O2-O9.5 stars using Far-Ultraviolet Spectroscopic Explorer archival data. The stars selected for the atlas were drawn from three populations: Galactic main-sequence (classes III-V) stars, supergiants, and main-sequence stars in the Magellanic Clouds, which have low metallicities. For several of these stars, we have prepared FITS files comprised of pairs of merged spectra for user access via the Multimission Archive at Space Telescope (MAST). We chose spectra from the first population with spectral types O4, O5, O6, O7, O8, and O9.5 and used them to compile tables and figures with identifications of all possible atmospheric and interstellar medium lines in the region 949-1188Ã…. Our identified line totals for these six representative spectra are 821 (500), 992 (663), 1077 (749), 1178 (847), 1359 (1001), and 1798 (1392) lines, respectively, where the numbers in parentheses are the totals of lines formed in the atmospheres, according to spectral synthesis models. The total number of unique atmospheric identifications for the six main-sequence O-star template spectra is 1792, whereas the number of atmospheric lines in common to these spectra is 300. The number of identified lines decreases toward earlier types (increasing effective temperature), while the percentages of "missed" features (unknown lines not predicted from our spectral syntheses) drop from a high of 8% at type B0.2, from our recently published B-star far-UV atlas (Cat. J/ApJS/186/175), to 1%-3% for type O spectra. The percentages of overpredicted lines are similar, despite their being much higher for B-star spectra. (4 data files).
Erratum: ``A Grid of Non-LTE Line-blanketed Model Atmospheres of O-Type Stars'' (ApJS, 146, 417 [2003])
Lanz, Thierry; Hubeny, Ivan
We have constructed a comprehensive grid of 680 metal line-blanketed, non-LTE, plane-parallel, hydrostatic model atmospheres for the basic parameters appropriate to O-type stars. The OSTAR2002 grid considers 12 values of effective temperatures, 27,500K<=Teff<=55,000 K with 2500 K steps, eight surface gravities, 3.0<=logg<=4.75 with 0.25 dex steps, and 10 chemical compositions, from metal-rich relative to the Sun to metal-free. The lower limit of logg for a given effective temperature is set by an approximate location of the Eddington limit. The selected chemical compositions have been chosen to cover a number of typical environments of massive stars: the Galactic center, the Magellanic Clouds, blue compact dwarf galaxies like I Zw 18, and galaxies at high redshifts. The paper contains a description of the OSTAR2002 grid and some illustrative examples and comparisons. The complete OSTAR2002 grid is available at our Web site at ApJS, 146, 417 [2003]. Laboratory for Astronomy and Solar Physics, NASA Goddard Space Flight Center, Code 681, Greenbelt, MD 20771.
Fluctuations at the blue edge of saturated wind lines in IUE spectra of O-type stars
Owocki, Stanley P.; Fullerton, Alex
We examine basic issues involved in synthesizing resonance-line profiles from 1-D, dynamical models of highly structured hot-star winds. Although these models exhibit extensive variations in density as well as velocity, the density scale length is still typically much greater than the Sobolev length. The line transfer is thus treated using a Sobolev approach, as generalized by Rybicki & Hummer (1978) to take proper account of the multiple Sobolev resonances arising from the nonmonotonic velocity field. The resulting reduced-Lambda-matrix equation describing nonlocal coupling of the source function is solved by iteration, and line profiles and then derived from formal solution integration using this source function. The more appropriate methods that instead use either a stationary or a structured, local source function yield qualitatively similar line-profiles, but are found to violate photon conservation by 10 percent or more. The full results suggest that such models may indeed be able to reproduce naturally some of the qualitative properties long noted in observed UV line profiles, such as discrete absorption components in unsaturated lines, or the blue-edge variability in saturated lines. However, these particular models do not yet produce the black absorption troughs commonly observed in saturated lines, and it seems that this and other important discrepancies (e.g., in acceleration time scale of absorption components) may require development of more complete models that include rotation and other 2-D and/or 3-D effects.
Hα Monitoring of Early-Type Emission Line Stars
Souza, Steven P.; Boettcher, E.; Wilson, S.; Hosek, M.
We have begun a narrowband imaging program to monitor Hα emission in early-type stars in young open clusters and associations. A minority of early-type stars, particularly Be stars, show Hα in emission due to extended atmospheres and non-equilibrium conditions. Emission features commonly vary irregularly over a range of timescales (Porter, J.M. & Rivinus, T., P.A.S.P. 115:1153-1170, 2003). Some of the brightest such stars, e.g. γ Cas, have been spectroscopically monitored for Hα variability to help constrain models of the unstable disk, but there is relatively little ongoing monitoring in samples including fainter stars (Peters, G., Be Star Newsletter 39:3, 2009). Our program uses matched 5nm-wide on-band (656nm) and off-band (645nm) filters, in conjunction with the Hopkins Observatory 0.6-m telescope and CCD camera. Aperture photometry is done on all early-type stars in each frame, and results expressed as on-band to off-band ratios. Though wavelength-dependent information is lost compared with spectroscopy, imaging allows us to observe much fainter (and therefore many more) objects. Observing young clusters, rather than individual target stars, allows us to record multiple known and candidate emission line stars per frame, and provides multiple "normal" reference stars of similar spectral type. Observations began in the summer of 2010. This project has the potential to produce significant amounts of raw data, so a semi-automated data reduction process has been developed, including astrometric and photometric tasks. Early results, including some preliminary light curves and recovery of known Be stars at least as faint as R=13.9, are presented. We gratefully acknowledge support for student research through an REU grant to the Keck Northeast Astronomy Consortium from the National Science Foundation, and from the Division III Research Funding Committee of Williams College.
The Lyman-Continuum Fluxes and Stellar Parameters of O and Early B-Type Stars
Vacca, William D.; Garmany, Catherine D.; Shull, J. Michael
Using the results of the most recent stellar atmosphere models applied to a sample of hot stars, we construct calibrations of effective temperature (T(sub eff)), and gravity (log(sub g)) with a spectral type and luminosity class for Galactic 0-type and early B-type stars. From the model results we also derive an empirical relation between the bolometric correction and T(sub eff) and log g. Using a sample of stars with known distances located in OB associations in the Galaxy and the Large Magellanic Cloud, we derive a new calibration of M(sub v) with spectral class. With these new calibrations and the stellar atmosphere models of Kurucz, we calculate the physical parameters and ionizing photon luminosities in the H(0) and He(0) continua for O and early B-type stars. We find substantial differences between our values of the Lyman- continuum luminosity and those reported in the literature. We also discuss the systematic discrepancy between O-type stellar masses derived from spectroscopic models and those derived from evolutionary tracks. Most likely, the cause of this 'mass discrepancy' lies primarily in the atmospheric models, which are plane parallel and hydrostatic and therefore do not account for an extended atmosphere and the velocity fields in a stellar wind. Finally, we present a new computation of the Lyman-continuum luminosity from 429 known O stars located within 2.5 kpc of the Sun. We find the total ionizing luminosity from this population ((Q(sub 0)(sup T(sub ot))) = 7.0 x 10(exp 51) photons/s) to be 47% larger than that determined using the Lyman continuum values tabulated by Panagia.
Metallicities and Nucleosynthesis Patterns in Early Generation Halo Stars
Beers, T.
I review our present knowledge of the Metallicity Distribution Function of stars in the low-metallicity tail of the halo population of the Galaxy, and the variety of observed elemental signatures that might be associated with particular astrophysical origins in the early Universe. Such signatures include stars that exhibit (a) highly and mildly enhanced r-process element ratios, as compared to the solar ratios, (b) highly s-process enriched stars, (c) stars showing large enrichments of both the r- and and s-process elements, and (d) stars that are greatly enhanced in the light element species, such as CNO, and (in some cases) the alpha elements. Because the stars in which these characteristics are observed all have metallicity [Fe/H] ≤ -2.5, they are inferred to have formed no more than 0.5-1 Gyrs after the Big Bang, prior to the final assemblage of the Milky Way. As such, they provide our best available probes of the nature of early element producers, such as Type II SN and hypernovae, as well as binaries that included (now deceased) stars of intermediate (1.5 - 3 Mo) masses. I outline ongoing and future plans for dramatically accelerating the pace of discovery of these rare, but clearly important, objects. Partial support for this work has been received from NSF grants AST 00-98508 and AST 00-98549, and from JINA, the Joint Institute for Nuclear Astrophysics, an NSF Physics Frontier Center.
Early Results from NICER Observations of Accreting Neutron Stars
Chakrabarty, Deepto; Ozel, Feryal; Arzoumanian, Zaven; Gendreau, Keith C.; Bult, Peter; Cackett, Ed; Chenevez, Jerome; Fabian, Andy; Guillot, Sebastien; Guver, Tolga; Homan, Jeroen; Keek, Laurens; Lamb, Frederick; Ludlam, Renee; Mahmoodifar, Simin; Markwardt, Craig B.; Miller, Jon M.; Psaltis, Dimitrios; Strohmayer, Tod E.; Wilson-Hodge, Colleen A.; Wolff, Michael T.
The Neutron Star Interior Composition Explorer (NICER) offers significant new capabilities for the study of accreting neuton stars relative to previous X-ray missions including large effective area, low background, and greatly improved low-energy response. The NICER Burst and Accretion Working Group has designed a 2 Ms observation program to study a number of phenomena in accreting neutron stars including type-I X-ray bursts, superbursts, accretion-powered pulsations, quasi-periodic oscillations, and accretion disk reflection spectra. We present some early results from the first six months of the NICER mission.
Nearby star cluster yields insights into early universe
The nebula offers a unique opportunity for a close-up glimpse of the "firestorm" accompanying the birth of extremely massive stars, each blazing with the brilliance of 300,000 of our suns. Such galactic fireworks were much more common billions of years ago in the early universe, when most star formation took place. "This is giving us new insights into the physical mechanisms governing star formation in far away galaxies that existed long ago," says Mohammad Heydari-Malayeri (Paris Observatory, France), who headed the international team of astronomers who made the discovery using Hubble's Wide Field and Planetary Camera 2. Because these stars are deficient in heavier elements, they also evolve much like the universe's earliest stars, which were made almost exclusively of the primordial elements hydrogen and helium that were created in the big bang. The Small Magellanic Cloud is a unique laboratory for studying star formation in the early universe since it is the closest and best seen galaxy containing so-called "metal-poor" first- and second -generation type stars. These observations show that massive stars may form in groups. "As a result, it is more likely some of these stars are members of double and multiple star systems," says Heydari-Malayeri. "The multiple systems will affect stellar evolution considerably by ejecting a great deal of matter into space." This furious rate of mass loss from these stars is evident in the Hubble picture, which reveals dramatic shapes sculpted in the nebula's wall of glowing gases by violent stellar winds and shock waves. "This implies a very turbulent environment typical of young star formation regions," Heydari-Malayeri adds. He believes one of the members of the cluster may be an extremely rare and short-lived class of super-hot star (50,000 degrees Kelvin) called a Wolf-Rayet. This star represents a violent, transitional phase in the final years of a massive star's existence - before it ultimately explodes as a supernova. "If
NEARBY MASSIVE STAR CLUSTER YIELDS INSIGHTS INTO EARLY UNIVERSE
A NASA Hubble Space Telescope 'family portrait' of young, ultra-bright stars nested in their embryonic cloud of glowing gases. The celestial maternity ward, called N81, is located 200,000 light-years away in the Small Magellanic Cloud (SMC), a small irregular satellite galaxy of our Milky Way. Hubble's exquisite resolution allows astronomers to pinpoint 50 separate stars tightly packed in the nebula's core within a 10 light-year diameter - slightly more than twice the distance between earth and the nearest star to our sun. The closest pair of stars is only 1/3 of a light-year apart (0.3 arcseconds in the sky). This furious rate of mass loss from these super-hot stars is evident in the Hubble picture that reveals dramatic shapes sculpted in the nebula's wall of glowing gases by violent stellar winds and shock waves. A pair of bright stars in the center of the nebula is pouring out most of the ultraviolet radiation to make the nebula glow. Just above them, a small dark knot is all that's left of the cold cloud of molecular hydrogen and dust the stars were born from. Dark absorption lanes of residual dust trisect the nebula. The nebula offers a unique opportunity for a close-up glimpse at the 'firestorm' accompanying the birth of extremely massive stars, each blazing with the brilliance of 300,000 of our suns. Such galactic fireworks were much more common billions of years ago in the early universe, when most star formation took place. The 'natural-color' view was assembled from separate images taken with the Wide Field and Planetary Camera 2, in ultraviolet light and two narrow emission lines of ionized Hydrogen (H-alpha, H-beta). The picture was taken on September 4, 1997. Credit: Mohammad Heydari-Malayeri (Paris Observatory, France), NASA/ESA
Five-Star Schools: Defining Quality in Early Childhood Programs
Hertzog, Nancy B.
Hakeem, Emily, Jose, and Latisha are all entering preschool in the fall. Their mothers are looking for the highest quality early childhood program they can find. Is there a guide for them to find a five-star program? Are all certified or accredited programs of equal quality? How do these parents and guardians know what defines quality in early…
Centaurus X-3. [early x-ray binary star spectroscopy
Hutchings, J. B.; Cowley, A. P.; Crampton, D.; Van Paradus, J.; White, N. E.
Spectroscopic observations of Krzeminski's star at dispersions 25-60 A/mm are described. The primary is an evolved star of type O6-O8(f) with peculiarities, some of which are attributable to X-ray heating. Broad emission lines at 4640A (N III), 4686 A(He II) and H-alpha show self-absorption and do not originate entirely from the region near the X-ray star. The primary is not highly luminous (bolometric magnitude about -9) and does not show signs of an abnormally strong stellar wind. The X-ray source was 'on' at the time of optical observations. Orbital parameters are presented for the primary, which yield masses of 17 + or - 2 and 1.0 + or - 3 solar masses for the stars. The optical star is undermassive for its luminosity, as are other OB-star X-ray primaries. The rotation is probably synchronized with the orbital motion. The distance to Cen X-3 is estimated to be 10 + or - 1 kpc. Basic data for 12 early-type X-ray primaries are discussed briefly
Reionization of Hydrogen and Helium by Early Stars and Quasars
Wyithe, J. Stuart B.; Loeb, Abraham
We compute the reionization histories of hydrogen and helium caused by the ionizing radiation fields produced by stars and quasars. For the quasars we use a model based on halo-merger rates that reproduces all known properties of the quasar luminosity function at high redshifts. The less constrained properties of the ionizing radiation produced by stars are modeled with two free parameters: (i) a transition redshift, ztran, above which the stellar population is dominated by massive, zero-metallicity stars and below which it is dominated by a Scalo mass function; and (ii) the product of the escape fraction of stellar ionizing photons from their host galaxies and the star formation efficiency, fescf*. We constrain the allowed range of these free parameters at high redshifts on the basis of the lack of the H I Gunn-Peterson trough at z<~6 and the upper limit on the total intergalactic optical depth for electron scattering, Ï"es<0.18, from recent cosmic microwave background (CMB) experiments. We find that quasars ionize helium by a redshift z~4, but cannot reionize hydrogen by themselves before z~6. A major fraction of the allowed combinations of fescf* and ztran leads to an early peak in the ionized fraction because of the presence of metal-free stars at high redshifts. This sometimes results in two reionization epochs, namely, an early H II or He III overlap phase followed by recombination and a second overlap phase. Even if early overlap is not achieved, the peak in the visibility function for scattering of the CMB often coincides with the early ionization phase rather than with the actual reionization epoch. Consequently, Ï"es does not correspond directly to the reionization redshift. We generically find values of Ï"es>~7%, which should be detectable by the MAP satellite.
Spectral analysis of early-type stars using a genetic algorithm based fitting method
Mokiem, M. R.; de Koter, A.; Puls, J.; Herrero, A.; Najarro, F.; Villamariz, M. R.
We present the first automated fitting method for the quantitative spectroscopy of O- and early B-type stars with stellar winds. The method combines the non-LTE stellar atmosphere code fastwind from Puls et al. (2005, A&A, 435, 669) with the genetic algorithm based optimization routine pikaia from Charbonneau (1995, ApJS, 101, 309), allowing for a homogeneous analysis of upcoming large samples of early-type stars (e.g. Evans et al. 2005, A&A, 437, 467). In this first implementation we use continuum normalized optical hydrogen and helium lines to determine photospheric and wind parameters. We have assigned weights to these lines accounting for line blends with species not taken into account, lacking physics, and/or possible or potential problems in the model atmosphere code. We find the method to be robust, fast, and accurate. Using our method we analysed seven O-type stars in the young cluster Cyg OB2 and five other Galactic stars with high rotational velocities and/or low mass loss rates (including 10 Lac, ζ Oph, and τ Sco) that have been studied in detail with a previous version of fastwind. The fits are found to have a quality that is comparable or even better than produced by the classical "by eye� method. We define errorbars on the model parameters based on the maximum variations of these parameters in the models that cluster around the global optimum. Using this concept, for the investigated dataset we are able to recover mass-loss rates down to ~6 × 10-8~M⊙ yr-1 to within an error of a factor of two, ignoring possible systematic errors due to uncertainties in the continuum normalization. Comparison of our derived spectroscopic masses with those derived from stellar evolutionary models are in very good agreement, i.e. based on the limited sample that we have studied we do not find indications for a mass discrepancy. For three stars we find significantly higher surface gravities than previously reported. We identify this to be due to differences in
A Grid of NLTE Line-blanketed Model Atmospheres of Early B-Type Stars
We have constructed a comprehensive grid of 1540 metal line-blanketed, NLTE, plane-parallel, hydrostatic model atmospheres for the basic parameters appropriate to early B-type stars. The BSTAR2006 grid considers 16 values of effective temperatures, 15,000 K<=Teff<=30,000 K with 1000 K steps, 13 surface gravities, 1.75<=logg<=4.75 with 0.25 dex steps, six chemical compositions, and a microturbulent velocity of 2 km s-1. The lower limit of logg for a given effective temperature is set by an approximate location of the Eddington limit. The selected chemical compositions range from twice to one-tenth of the solar metallicity and metal-free. Additional model atmospheres for B supergiants (logg<=3.0) have been calculated with a higher microturbulent velocity (10 km s-1) and a surface composition that is enriched in helium and nitrogen and depleted in carbon. This new grid complements our earlier OSTAR2002 grid of O-type stars (our Paper I). The paper contains a description of the BSTAR2006 grid and some illustrative examples and comparisons. NLTE ionization fractions, bolometric corrections, radiative accelerations, and effective gravities are obtained over the parameter range covered by the grid. By extrapolating radiative accelerations, we have determined an improved estimate of the Eddington limit in absence of rotation between 55,000 and 15,000 K. The complete BSTAR2006 grid is available at the TLUSTY Web site.
Star Formation-Driven Winds in the Early Universe
Peek, Matthew; Lundgren, Britt; Brammer, Gabriel
Measuring the extent of star formation-driven winds from galaxies in the early universe is crucial for understanding of how galaxies evolve over cosmic time. Using WFC3/IR grism data from the Hubble Space Telescope (HST), we have measured the star formation rates and star formation rate surface densities of several hundred galaxies at redshift (z) = 1, when the universe was roughly half its present age. The galaxies we examine are also probed by background quasars, whose spectra provide information about the extent of metal-enriched gas in their halos. We use a computational pipeline to measure the density of the star formation in each galaxy and correlate these measurements with detections of Mg II absorption in nearby quasar spectra from the Sloan Digital Sky Survey. Our preliminary results support a model in which galaxies with high SFR surface densities drive metal-enriched gas out of the disk and into these galaxies' extended halos, where that gas is detected in the spectra of more distant quasars.
The Formation and Early Evolution of Embedded Massive Star Clusters
Barnes, Peter
We propose to combine Spitzer, WISE, Herschel, and other archival spacecraft data with an existing ground- and space-based mm-wave to near-IR survey of molecular clouds over a large portion of the Milky Way, in order to systematically study the formation and early evolution of massive stars and star clusters, and provide new observational calibrations for a theoretical paradigm of this key astrophysical problem. Central Objectives: The Galactic Census of High- and Medium-mass Protostars (CHaMP) is a large, unbiased, uniform, and panchromatic survey of massive star and cluster formation and early evolution, covering 20°x6° of the Galactic Plane. Its uniqueness lies in the comprehensive molecular spectroscopy of 303 massive dense clumps, which have also been included in several archival spacecraft surveys. Our objective is a systematic demographic analysis of massive star and cluster formation, one which has not been possible without knowledge of our CHaMP cloud sample, including all clouds with embedded clusters as well as those that have not yet formed massive stars. For proto-clusters deeply embedded within dense molecular clouds, analysis of these space-based data will: 1. Yield a complete census of Young Stellar Objects in each cluster. 2. Allow systematic measurements of embedded cluster properties: spectral energy distributions, luminosity functions, protostellar and disk fractions, and how these vary with cluster mass, age, and density. Combined with other, similarly complete and unbiased infrared and mm data, CHaMP's goals include: 3. A detailed comparison of the embedded stellar populations with their natal dense gas to derive extinction maps, star formation efficiencies and feedback effects, and the kinematics, physics, and chemistry of the gas in and around the clusters. 4. Tying the demographics, age spreads, and timescales of the clusters, based on pre-Main Sequence evolution, to that of the dense gas clumps and Giant Molecular Clouds. 5. A
Fundamental properties of nearby single early B-type stars
Nieva, María-Fernanda; Przybilla, Norbert
Aims: Fundamental parameters of a sample of 26 apparently slowly-rotating single early B-type stars in OB associations and in the field within a distance of ≲400 pc from the Sun are presented and compared to high-precision data from detached eclipsing binaries (DEBs). Together with surface abundances for light elements the data are used to discuss the evolutionary status of the stars in context of the most recent Geneva grid of models for core hydrogen-burning stars in the mass-range ~6 to 18 M⊙ at metallicity Z = 0.014. Methods: The fundamental parameters are derived on the basis of accurate and precise atmospheric parameters determined earlier by us from non-LTE analyses of high-quality spectra of the sample stars, utilising the new Geneva stellar evolution models. Results: Evolutionary masses plus radii and luminosities are determined to better than typically 5%, 10%, and 20% uncertainty, respectively, facilitating the mass-radius and mass-luminosity relationships to be recovered for single core hydrogen-burning objects with a similar precision as derived from DEBs. Good agreement between evolutionary and spectroscopic masses is found. Absolute visual and bolometric magnitudes are derived to typically ~0.15-0.20 mag uncertainty. Metallicities are constrained to better than 15-20% uncertainty and tight constraints on evolutionary ages of the stars are provided. Overall, the spectroscopic distances and ages of individual sample stars agree with independently derived values for the host OB associations. Signatures of mixing with CN-cycled material are found in 1/3 of the sample stars. Typically, these are consistent with the amount predicted by the new Geneva models with rotation. The presence of magnetic fields appears to augment the mixing efficiency. In addition, a few objects are possibly the product of binary evolution. In particular, the unusual characteristics of τ Sco point to a blue straggler nature, due to a binary merger. Conclusions: The accuracy
New insight into the physics of atmospheres of early type stars
Lamers, H. J. G. L. M.
The phenomenon of mass loss and stellar winds from hot stars are discussed. The mass loss rate of early type stars increases by about a factor of 100 to 1000 during their evolution. This seems incompatible with the radiation driven wind models and may require another explanation for the mass loss from early type stars. The winds of early type stars are strongly variable and the stars may go through active phases. Eclipses in binary systems by the stellar winds can be used to probe the winds. A few future IUE studies are suggested.
Observations of Nonthermal Radio Emission from Early-type Stars
Abbott, D. C.; Bieging, J. H.; Churchwell, E.
As a part of a wider survey of radio emission from O, B, and Wolf-Rayet (WR) stars, five new stars whose radio emission is dominated by a nonthermal mechanism of unknown origin were discovered. From statistics of distance-limited samples of stars, it is estimated that the minimum fraction of stars which are nonthermal emitters is 25% for the OB stars and 10% for the WR stars. The characteristics of this new class of nonthermal radio emitter are investigated.
Structural analysis of star-forming blue early-type galaxies. Merger-driven star formation in elliptical galaxies
George, Koshy
Context. Star-forming blue early-type galaxies at low redshift can give insight to the stellar mass growth of L⋆ elliptical galaxies in the local Universe. Aims: We wish to understand the reason for star formation in these otherwise passively evolving red and dead stellar systems. The fuel for star formation can be acquired through recent accretion events such as mergers or flyby. The signatures of such events should be evident from a structural analysis of the galaxy image. Methods: We carried out structural analysis on SDSS r-band imaging data of 55 star-forming blue elliptical galaxies, derived the structural parameters, analysed the residuals from best-fit to surface brightness distribution, and constructed the galaxy scaling relations. Results: We found that star-forming blue early-type galaxies are bulge-dominated systems with axial ratio >0.5 and surface brightness profiles fitted by Sérsic profiles with index (n) mostly >2. Twenty-three galaxies are found to have n< 2; these could be hosting a disc component. The residual images of the 32 galaxy surface brightness profile fits show structural features indicative of recent interactions. The star-forming blue elliptical galaxies follow the Kormendy relation and show the characteristics of normal elliptical galaxies as far as structural analysis is concerned. There is a general trend for high-luminosity galaxies to display interaction signatures and high star formation rates. Conclusions: The star-forming population of blue early-type galaxies at low redshifts could be normal ellipticals that might have undergone a recent gas-rich minor merger event. The star formation in these galaxies will shut down once the recently acquired fuel is consumed, following which the galaxy will evolve to a normal early-type galaxy.
Star formation in globular clusters and dwarf galaxies and implications for the early evolution of galaxies
Lin, Douglas N. C.; Murray, Stephen D.
Based upon the observed properties of globular clusters and dwarf galaxies in the Local Group, we present important theoretical constraints on star formation in these systems. These constraints indicate that protoglobular cluster clouds had long dormant periods and a brief epoch of violent star formation. Collisions between protocluster clouds triggered fragmentation into individual stars. Most protocluster clouds dispersed into the Galactic halo during the star formation epoch. In contrast, the large spread in stellar metallicity in dwarf galaxies suggests that star formation in their pregenitors was self-regulated: we propose the protocluster clouds formed from thermal instability in the protogalactic clouds and show that a population of massive stars is needed to provide sufficient UV flux to prevent the collapsing protogalactic clouds from fragmenting into individual stars. Based upon these constraints, we propose a unified scenario to describe the early epochs of star formation in the Galactic halo as well as the thick and thin components of the Galactic disk.
A Rare Early-type Star Revealed in the Wing of the Small Magellanic Cloud
Evans, C. J.; Hainich, R.; Oskinova, L. M.; Gallagher, J. S., III; Chu, Y.-H.; Gruendl, R. A.; Hamann, W.-R.; Hénault-Brunet, V.; Todt, H.
Sk 183 is the visually brightest star in the N90 nebula, a young star-forming region in the Wing of the Small Magellanic Cloud (SMC). We present new optical spectroscopy from the Very Large Telescope which reveals Sk 183 to be one of the most massive O-type stars in the SMC. Classified as an O3-type dwarf on the basis of its nitrogen spectrum, the star also displays broadened He I absorption, which suggests a later type. We propose that Sk 183 has a composite spectrum and that it is similar to another star in the SMC, MPG 324. This brings the number of rare O2- and O3-type stars known in the whole of the SMC to a mere four. We estimate physical parameters for Sk 183 from analysis of its spectrum. For a single-star model, we estimate an effective temperature of 46 ± 2 kK, a low mass-loss rate of ~10-7 M ⊙ yr-1, and a spectroscopic mass of 46+9 -8 M ⊙ (for an adopted distance modulus of 18.7 mag to the young population in the SMC Wing). An illustrative binary model requires a slightly hotter temperature (~47.5 kK) for the primary component. In either scenario, Sk 183 is the earliest-type star known in N90 and will therefore be the dominant source of hydrogen-ionizing photons. This suggests Sk 183 is the primary influence on the star formation along the inner edge of the nebula.
Early-Type Galaxy Star Formation Histories in Different Environments
Fitzpatrick, Patrick; Graves, G.
We use very high-S/N stacked spectra of ˜29,000 nearby quiescent early-type galaxies (ETGs) from the Sloan Digital Sky Survey (SDSS) to investigate variations in their star formation histories (SFHs) with environment at fixed position along and perpendicular to the Fundamental Plane (FP). We separate galaxies in the three-dimensional FP space defined by galaxy effective radius Re, central stellar velocity dispersion σ, and surface brightness residual from the FP, ΔIe. We use the SDSS group catalogue of Yang et al. to further separate galaxies into three categories by their "identities� within their respective dark matter halos: central "Brightest Group Galaxies� (BGGs); Satellites; and Isolateds (those which are "most massive� in a dark matter halo with no Satellites). Within each category, we construct high-S/N mean stacked spectra to determine mean singleburst ages, [Fe/H], and [Mg/Fe] based on the stellar population synthesis models of R. Schiavon. This allows us to study variations in the stellar population properties (SPPs) with local group environment at fixed structure (i.e., fixed position in FP-space). We find that the SFHs of quiescent ETGs are almost entirely determined by their structural parameters σ and ΔIe. Any variation with local group environment at fixed structure is only slight: Satellites have the oldest stellar populations, 0.02 dex older than BGGs and 0.04 dex older than Isolateds; BGGs have the highest Fe-enrichments, 0.01 dex higher than Isolateds and 0.02 dex higher than Satellites; there are no differences in Mg-enhancement between BGGs, Isolateds, and Satellites. Our observation that, to zeroth-order, the SFHs of quiescent ETGs are fully captured by their structures places important qualitative constraints on the degree to which late-time evolutionary processes (those which occur after a galaxy's initial formation and main star-forming lifetime) can alter their SFHs/structures.
The magnetic early B-type stars I: magnetometry and rotation
Shultz, M. E.; Wade, G. A.; Rivinius, Th; Neiner, C.; Alecian, E.; Bohlender, D.; Monin, D.; Sikora, J.; MiMeS Collaboration; BinaMIcS Collaboration
The rotational and magnetic properties of many magnetic hot stars are poorly characterized, therefore the Magnetism in Massive Stars and Binarity and Magnetic Interactions in various classes of Stars collaborations have collected extensive high-dispersion spectropolarimetric data sets of these targets. We present longitudinal magnetic field measurements for 52 early B-type stars (B5-B0), with which we attempt to determine their rotational periods Prot. Supplemented with high-resolution spectroscopy, low-resolution Dominion Astrophysical Observatory circular spectropolarimetry, and archival Hipparcos photometry, we determined Prot for 10 stars, leaving only five stars for which Prot could not be determined. Rotational ephemerides for 14 stars were refined via comparison of new to historical magnetic measurements. The distribution of Prot is very similar to that observed for the cooler Ap/Bp stars. We also measured v sin i and vmac for all stars. Comparison to non-magnetic stars shows that v sin i is much lower for magnetic stars, an expected consequence of magnetic braking. We also find evidence that vmac is lower for magnetic stars. Least-squares deconvolution profiles extracted using single-element masks revealed widespread, systematic discrepancies in between different elements: this effect is apparent only for chemically peculiar stars, suggesting it is a consequence of chemical spots. Sinusoidal fits to H line measurements (which should be minimally affected by chemical spots), yielded evidence of surface magnetic fields more complex than simple dipoles in six stars for which this has not previously been reported; however, in all six cases, the second- and third-order amplitudes are small relative to the first-order (dipolar) amplitudes.
EVIDENCE FOR GRANULATION IN EARLY A-TYPE STARS
Kallinger, Thomas; Matthews, Jaymie M.
Stars with spectral types earlier than about F0 on (or close) to the main sequence have long been believed to lack observable surface convection, although evolutionary models of A-type stars do predict very thin surface convective zones. We present evidence for granulation in two {delta} Scuti stars of spectral type A2: HD 174936 and HD 50844. Recent analyses of space-based CoRoT data revealed up to some 1000 frequencies in the photometry of these stars. The frequencies were interpreted as individual pulsation modes. If true, there must be large numbers of nonradial modes of very high degree l which should suffermore » cancellation effects in disk-integrated photometry (even of high space-based precision). The p-mode interpretation of all the frequencies in HD 174936 and HD 50844 depends on the assumption of white (frequency-independent) noise. Our independent analyses of the data provide an alternative explanation: most of the peaks in the Fourier spectra are the signature of non-white granulation background noise, and less than about 100 of the frequencies are actual stellar p-modes in each star. We find granulation timescales which are consistent with scaling relations that describe cooler stars with known surface convection. If the granulation interpretation is correct, the hundreds of low-amplitude Fourier peaks reported in recent studies are falsely interpreted as independent pulsation modes and a significantly lower number of frequencies are associated with pulsation, consistent with only modes of low degree.« less
The VLT-FLAMES survey of massive stars: mass loss and rotation of early-type stars in the SMC
Mokiem, M. R.; de Koter, A.; Evans, C. J.; Puls, J.; Smartt, S. J.; Crowther, P. A.; Herrero, A.; Langer, N.; Lennon, D. J.; Najarro, F.; Villamariz, M. R.; Yoon, S.-C.
We have studied the optical spectra of a sample of 31 O-and early B-type stars in the Small Magellanic Cloud, 21 of which are associated with the young massive cluster NGC 346. Stellar parameters are determined using an automated fitting method (Mokiem et al. 2005, A&A, 441, 711), which combines the stellar atmosphere code FASTWIND (Puls et al. 2005, A&A, 435, 669) with the genetic algorithm based optimisation routine PIKAIA (Charbonneau 1995, ApJS, 101, 309). Comparison with predictions of stellar evolution that account for stellar rotation does not result in a unique age, though most stars are best represented by an age of 1-3 Myr. The automated method allows for a detailed determination of the projected rotational velocities. The present day v_r sin i distribution of the 21 dwarf stars in our sample is consistent with an underlying rotational velocity (v_r) distribution that can be characterised by a mean velocity of about 160 - 190 km s-1 and an effective half width of 100 - 150 km s-1. The vr distribution must include a small percentage of slowly rotating stars. If predictions of the time evolution of the equatorial velocity for massive stars within the environment of the SMC are correct (Maeder & Meynet 2001, A&A, 373, 555), the young age of the cluster implies that this underlying distribution is representative for the initial rotational velocity distribution. The location in the Hertzsprung-Russell diagram of the stars showing helium enrichment is in qualitative agreement with evolutionary tracks accounting for rotation, but not for those ignoring v_r. The mass loss rates of the SMC objects having luminosities of log L*/L⊙ ≳ 5.4 are in excellent agreement with predictions by Vink et al. (2001, A&A, 369, 574). However, for lower luminosity stars the winds are too weak to determine dot{M} accurately from the optical spectrum. Three targets were classifiedas Vz stars, two of which are located close to the theoretical zero-age main sequence. Three lower
Copernicus observations of the N v resonance doublet in 53 early-type stars
Abbott, D. C.; Bohlin, R. C.; Savage, B. D.
UV spectra in the wavelength interval 1170-1270 A are presented for 53 early-type stars ranging in spectral type from O6.5 V to B2.5 IV. The sample includes four Wolf-Rayet stars, seven known Oe-Be stars, and six galactic halo OB stars. A qualitative analysis of the stellar N v doublet reveals that: (1) N v is present in all stars hotter and more luminous than type B0 for the main sequence, B1 for giants, and B2 for supergiants; (2) shell components of N v and an unidentified absorption feature at 1230 A are present in about half of the stars; (3) the column density of N v is well correlated with bolometric luminosity over the spectral range O6 to B2; and (4) the ratio of emission to absorption equivalent width is a factor of 2 smaller in the main sequence stars than in supergiants, which suggests that the wind structure changes as a star evolves. For several stars, this ratio is too small to be explained by traditional wind models.
Evaluation of Delaware Stars for Early Success: Year 1 Report. Research Report
Schwartz, Heather L.; Karoly, Lynn A.; Le, Vi-Nhuan; Tamargo, Jennifer; Setodji, Claude Messan
Delaware was in the first group of states to receive a federal grant in 2012 to improve early care and education services and increase the number of infants, toddlers, and preschool-age children in high-quality programs. One component of the state's grant is a rigorous validation process for Delaware Stars for Early Success, a voluntary quality…
What the Most Metal-poor Stars Tell Us About the Early Universe
Frebel, Anna
The chemical evolution of the Galaxy and the early Universe is a key topic in modern astrophysics. The most metal-poor Galactic halo stars are now frequently used in an attempt to reconstruct the onset of the chemical and dynamical formation processes of the Galaxy. These stars are an easily-accessible local equivalent of the high-redshift Universe, and can thus be used to carry out field-field cosmology. The discovery of two astrophysically very important metal-poor objects has recently lead to a significant advance in the field. One object is the most iron-poor star yet found (with [Fe/H]=-5.4). The other stars displays the strongest known overabundances of heavy neutron-capture elements, such as uranium, and nucleo-chronometry yields a stellar age of 13 Gyr. Both stars already serve as benchmark objects for various theoretical studies with regard to nucleosynthesis processes in the early Galaxy. I will discuss how the abundance patterns of these and other metal-poor stars solidify and advance our understanding of the early Universe, and provide constraints on the nature of the first stars, as well as their explosion mechanisms and corresponding supernova nucleosynthesis yields. Large samples of these old objects are also employed to test theoretical predictions about the formation of the very first low-mass stars. In the near future, the combined power of near-field cosmology results with those of the next-generation facilities (e.g., MWA, JWST, GMT) may yield exceptional details about the formation processes of the first generations of stars and galaxies.
UBV and H. beta. photometry of faint early-type stars in Crux and Centaurus
Muzzio, J.C.; Feinstein, A.; Orsatti, A.M.
UBV and H..beta.. photoelectric observations of faint early-type stars in a small region in Crux near the open cluster Hogg 15 and another in Centaurus are presented. The data suggest large absorption in Crux and small absorption in Centaurus. The spread in the distance moduli of the observed stars seems to be in agreement with the view that a spiral arm is seen tangentially near l = 305/sup 0/.
The Copernicus observations - Interstellar or circumstellar material. [UV spectra of early stars
Steigman, G.; Strittmatter, P. A.; Williams, R. E.
It is suggested that the sharp absorption lines observed in the ultraviolet spectra of early-type stars by the Copernicus satellite may be entirely accounted for by the circumstellar material in the H II regions and associated transition zones around the observed stars. If this interpretation is correct, the Copernicus results yield little information on the state of any interstellar (as opposed to circumstellar) gas and, in particular, shed little light on the degree of element depletion in interstellar space.
Capelato, Hugo Vicente
We will begin our study with a more or less superficial inspection of the "forest" of stars that we see in the skies. The first thing we notice is that, as sources of light, they are much weaker than the Sun. Second, their apparent colors vary; from a bluish-white in most of them to a reddish-yellow, which is rarer. There is also a third aspect, though it is not very obvious to the naked eye: most of the stars group themselves in small families of two, three or more members. A good example is the Alpha Centauri, the closest star to us, which, in fact, is a triple system of stars. Another is the group of 7 stars that make up the Pleiades, which will be discussed later on. In fact, almost half of the stars are double systems with only two members, called binary stars. Most of these double stars, though together, are separated by several astronomical units (one astronomical unit, AU, is the distance from Earth to the sun: see Chapter 1), and revolve around each other over periods of several years. And yet the revolutions of some binary stars, separated by much smaller distances, occur in only a few hours! These stars are so close to each other that they can share enveloping material. Often this exchange occurs in a somewhat violent manner. Local explosions may occur, expelling matter away from the system. In other binary systems, where one of the components is a very compact, dense star, companion material flows more calmly, making up a light disk around the compact star.
SPECTROSCOPIC ANALYSIS OF METAL-POOR STARS FROM LAMOST: EARLY RESULTS
Li, Hai-Ning; Zhao, Gang; Wang, Liang
We report on early results from a pilot program searching for metal-poor stars with LAMOST and follow-up high-resolution observation acquired with the MIKE spectrograph attached to the Magellan II telescope. We performed detailed abundance analysis for eight objects with iron abundances [Fe/H] < -2.0, including five extremely metal-poor (EMP; [Fe/H] < -3.0) stars with two having [Fe/H] < -3.5. Among these objects, three are newly discovered EMP stars, one of which is confirmed for the first time with high-resolution spectral observations. Three program stars are regarded as carbon-enhanced metal-poor (CEMP) stars, including two stars with no enhancement in their neutron-capturemore » elements, which thus possibly belong to the class of CEMP-no stars; one of these objects also exhibits significant enhancement in nitrogen, and is thus a potential carbon and nitrogen-enhanced metal-poor star. The [X/Fe] ratios of the sample stars generally agree with those reported in the literature for other metal-poor stars in the same [Fe/H] range. We also compared the abundance patterns of individual program stars with the average abundance pattern of metal-poor stars and find only one chemically peculiar object with abundances of at least two elements (other than C and N) showing deviations larger than 0.5 dex. The distribution of [Sr/Ba] versus [Ba/H] agrees that an additional nucleosynthesis mechanism is needed aside from a single r-process. Two program stars with extremely low abundances of Sr and Ba support the prospect that both main and weak r-processes may have operated during the early phase of Galactic chemical evolution. The distribution of [C/N] shows that there are two groups of carbon-normal giants with different degrees of mixing. However, it is difficult to explain the observed behavior of the [C/N] of the nitrogen-enhanced unevolved stars based on current data.« less
Hazardous Early Days In (and Beyond) the Habitable Zones Around Ultra-Low-Mass Stars
Kastner, Joel
Although a majority of stars in the solar neighborhood are of mid- to late-M type, the magnetically-induced coronal (X-ray) and chromospheric (UV, H-alpha) activity of such stars remain essentially unexplored for the important age range 10-100 Myr. Such information on high-energy processes associated with young M stars would provide much-needed constraints on models of the effects of stellar irradiation on the physics and chemistry of planet-forming disks and newborn planets. In addition, X-ray and UV observations of ultra-low-mass young stars can serve to probe the (presently ill-defined) spectral type boundary that determines which very low-mass objects will eventually become M stars -- as opposed to brown dwarfs (BDs) -- following their pre-main sequence evolutionary stages. Via ADAP support, we have developed the GALEX Nearby Young Star Search (GALNYSS), a search method that combines GALEX, 2MASS, WISE and proper motion catalog information to identify nearby, young, lowmass stars. We have applied this method to identify ~2000 candidate young (10-100 Myr), low-mass (M-type) stars within 150 pc. These GALNYSS-identified young star candidates are distributed over the entire GALEX-covered sky, and their spectral types peak in the M3-4 range; followup optical spectroscopic work is ongoing (Rodriguez et al. 2013, ApJ, 774, 101). We now propose an ADA program to determine the X-ray properties of representative stars among these GALNYSS candidates, so as to confirm their youth and investigate the early evolution of coronal activity near the low-mass star/BD boundary and the effects of such activity on planet formation. Specifically, we will exploit the presence in the HEASARC archives of XMM-Newton and (to a lesser extent) Chandra X-ray Observatory data for a few dozen GALNYSS candidates that have been observed serendipitously by one or both of these space observatories. The proposed ADA program will yield the full reduction and analysis of these as-yet unexplored data
Solar-Type Stars with the Suppression of Convection at an Early Stage of Evolution
Oreshina, A. V.; Baturin, V. A.; Ayukov, S. V.; Gorshkov, A. B.
The evolution of a solar-mass star before and on the main sequence is analyzed in light of the diminished efficiency of convection in the first 500 Myr. A numerical simulation has been performed with the CESAM2k code. It is shown that the suppression of convection in the early stages of evolution leads to a somewhat higher lithium content than that predicted by the classical solar model. In addition, the star's effective temperature decreases. Ignoring this phenomenon may lead to errors in age and mass determinations for young stars (before the main sequence) from standard evolutionary tracks in the temperature-luminosity diagram. At a later stage of evolution, after 500 Myr, the efficiency of convection tends to the solar value. At this stage, the star's inner structure becomes classical; it does not depend on the previous history. On the contrary, the photospheric lithium abundance contains information about the star's past. In other words, there may exist main-sequence solar-mass stars of the same age (above 500 Myr), radius, and luminosity, yet with different photospheric lithium contents. The main results of this work add considerably to the popular method for determining the age of solar-type stars from lithium abundances.
DD 13 - A very young and heavily reddened early O star in the Large Magellanic Cloud
Conti, Peter S.; Fitzpatrick, Edward L.
This paper investigates the Large Magellanic Cloud star DD 13, which is likely the major ionizing source of the nebula N159A. New optical spectroscopy and new estimates of the broadband photometric properties of DD 13 are obtained. A spectral type of O3-O6 V, E(B-V) = 0.64, and M(V) = -6.93 is found. The spectral type cannot be more precisely defined due to contamination of the spectral data by nebular emission, obliterating the important He I classification lines. These results, plus a published estimate of the Lyman continuum photon injection rate into N159A, suggest that DD 13 actually consists of about 2-4 young, early O stars still enshrouded by their natal dust cloud. The star DD 13 may be a younger example of the type of tight cluster represented by the LMC 'star' Sk-66 deg 41, recently revealed to be composed of six or more components.
Delaware Stars for Early Success. QRS Profile. The Child Care Quality Rating System (QRS) Assessment
Child Trends, 2010
This paper presents a profile of Delaware's Stars for Early Success prepared as part of the Child Care Quality Rating System (QRS) Assessment Study. The profile consists of several sections and their corresponding descriptions including: (1) Program Information; (2) Rating Details; (3) Quality Indicators for Center-Based Programs; (4) Indicators…
An Evaluation of the Early Alert (STAR) Program at Central Piedmont Community College
Gammon, J. B.
Central Piedmont Community College is exploring ways to help at-risk students achieve academic success by utilizing an early-alert system called Success Through Academic Reporting (STAR). All First-Time, Full-time Degree-seeking students (FFD) receive an opportunity for follow-up services that support a centralized strategy, which has the…
Abundance profiling of extremely metal-poor stars and supernova properties in the early universe
Tominaga, Nozomu; Iwamoto, Nobuyuki; Nomoto, Ken'ichi, E-mail: tominaga@konan-u.ac.jp, E-mail: iwamoto.nobuyuki@jaea.go.jp, E-mail: nomoto@astron.s.u-tokyo.ac.jp
After the big bang nucleosynthesis, the first heavy element enrichment in the universe was made by a supernova (SN) explosion of a population (Pop) III star (Pop III SN). The abundance ratios of elements produced from Pop III SNe are recorded in abundance patterns of extremely metal-poor (EMP) stars. The observations of the increasing number of EMP stars have made it possible to statistically constrain the explosion properties of Pop III SNe. We present Pop III SN models whose nucleosynthesis yields well reproduce, individually, the abundance patterns of 48 such metal-poor stars as [Fe/H] ≲ – 3.5. We then derivemore » relations between the abundance ratios of EMP stars and certain explosion properties of Pop III SNe: the higher [(C + N)/Fe] and [(C + N)/Mg] ratios correspond to the smaller ejected Fe mass and the larger compact remnant mass, respectively. Using these relations, the distributions of the abundance ratios of EMP stars are converted to those of the explosion properties of Pop III SNe. Such distributions are compared with those of the explosion properties of present day SNe: the distribution of the ejected Fe mass of Pop III SNe has the same peak as that of the present day SNe but shows an extended tail down to ∼10{sup –2}-10{sup –5} M {sub ☉}, and the distribution of the mass of the compact remnant of Pop III SNe is as wide as that of the present-day, stellar-mass black holes. Our results demonstrate the importance of large samples of EMP stars obtained by ongoing and future EMP star surveys and subsequent high-dispersion spectroscopic observations in clarifying the nature of Pop III SNe in the early universe.« less
The chemical abundance analysis of normal early A- and late B-type stars
Fossati, L.; Ryabchikova, T.; Bagnulo, S.; Alecian, E.; Grunhut, J.; Kochukhov, O.; Wade, G.
Context: Modern spectroscopy of early-type stars often aims at studying complex physical phenomena such as stellar pulsation, the peculiarity of the composition of the photosphere, chemical stratification, the presence of a magnetic field, and its interplay with the stellar atmosphere and the circumstellar environment. Comparatively less attention is paid to identifying and studying the "normal� A- and B-type stars and testing how the basic atomic parameters and standard spectral analysis allow one to fit the observations. By contrast, this kind of study is paramount for eventually allowing one to correctly quantify the impact of the various physical processes that occur inside the atmospheres of A- and B-type stars. Aims: We wish to establish whether the chemical composition of the solar photosphere can be regarded as a reference for early A- and late B-type stars. Methods: We have obtained optical high-resolution, high signal-to-noise ratio spectra of three slowly rotating early-type stars (HD 145788, 21 Peg and π Cet) that show no obvious sign of chemical peculiarity, and performed a very accurate LTE abundance analysis of up to 38 ions of 26 elements (for 21 Peg), using a vast amount of spectral lines visible in the spectral region covered by our spectra. Results: We provide an exhaustive description of the abundance characteristics of the three analysed stars with a critical review of the line parameters used to derive the abundances. We compiled a table of atomic data for more than 1100 measured lines that may be used in the future as a reference. The abundances we obtained for He, C, Al, S, V, Cr, Mn, Fe, Ni, Sr, Y, and Zr are compatible with the solar ones derived with recent 3D radiative-hydrodynamical simulations of the solar photosphere. The abundances of the remaining studied elements show some degree of discrepancy compared to the solar photosphere. Those of N, Na, Mg, Si, Ca, Ti, and Nd may well be ascribed to non-LTE effects; for P, Cl, Sc and
Exploring simulated early star formation in the context of the ultrafaint dwarf galaxies
Corlies, Lauren; Johnston, Kathryn V.; Wise, John H.
Ultrafaint dwarf galaxies (UFDs) are typically assumed to have simple, stellar populations with star formation ending at reionization. Yet as the observations of these galaxies continue to improve, their star formation histories (SFHs) are revealed to be more complicated than previously thought. In this paper, we study how star formation, chemical enrichment, and mixing proceed in small, dark matter haloes at early times using a high-resolution, cosmological, hydrodynamical simulation. The goals are to inform the future use of analytic models and to explore observable properties of the simulated haloes in the context of UFD data. Specifically, we look at analytic approaches that might inform metal enrichment within and beyond small galaxies in the early Universe. We find that simple assumptions for modelling the extent of supernova-driven winds agree with the simulation on average, whereas inhomogeneous mixing and gas flows have a large effect on the spread in simulated stellar metallicities. In the context of the UFDs, this work demonstrates that simulations can form haloes with a complex SFH and a large spread in the metallicity distribution function within a few hundred Myr in the early Universe. In particular, bursty and continuous star formation are seen in the simulation and both scenarios have been argued from the data. Spreads in the simulated metallicities, however, remain too narrow and too metal-rich when compared to the UFDs. Future work is needed to help reduce these discrepancies and advance our interpretation of the data.
Magnifying the Early Episodes of Star Formation: Super Star Clusters at Cosmological Distances
Vanzella, E.; Castellano, M.; Meneghetti, M.; Mercurio, A.; Caminha, G. B.; Cupani, G.; Calura, F.; Christensen, L.; Merlin, E.; Rosati, P.; Gronke, M.; Dijkstra, M.; Mignoli, M.; Gilli, R.; De Barros, S.; Caputi, K.; Grillo, C.; Balestra, I.; Cristiani, S.; Nonino, M.; Giallongo, E.; Grazian, A.; Pentericci, L.; Fontana, A.; Comastri, A.; Vignali, C.; Zamorani, G.; Brusa, M.; Bergamini, P.; Tozzi, P.
We study the spectrophotometric properties of a highly magnified (μ ≃ 40{--}70) pair of stellar systems identified at z = 3.2222 behind the Hubble Frontier Field galaxy cluster MACS J0416. Five multiple images (out of six) have been spectroscopically confirmed by means of VLT/MUSE and VLT/X-Shooter observations. Each image includes two faint ({m}{UV}≃ 30.6), young (≲ 100 Myr), low-mass (< {10}7 {M}⊙ ), low-metallicity (12 + Log(O/H) ≃ 7.7, or 1/10 solar), and compact (30 pc effective radius) stellar systems separated by ≃ 300 pc after correcting for lensing amplification. We measured several rest-frame ultraviolet and optical narrow ({σ }v≲ 25 km s-1) high-ionization lines. These features may be the signature of very hot (T> {{50,000}} K) stars within dense stellar clusters, whose dynamical mass is likely dominated by the stellar component. Remarkably, the ultraviolet metal lines are not accompanied by Lyα emission (e.g., C IV/Lyα > 15), despite the fact that the Lyα line flux is expected to be 150 times brighter (inferred from the Hβ flux). A spatially offset, strongly magnified (μ > 50) Lyα emission with a spatial extent ≲ 7.6 kpc2 is instead identified 2 kpc away from the system. The origin of such a faint emission could be the result of fluorescent Lyα induced by a transverse leakage of ionizing radiation emerging from the stellar systems and/or may be associated with an underlying and barely detected object (with {m}{UV}> 34 de-lensed). This is the first confirmed metal-line emitter at such low-luminosity and redshift without Lyα emission—suggesting that, at least in some cases, a non-uniform covering factor of the neutral gas might hamper the Lyα detection. Based on observations collected at the European Southern Observatory for Astronomical research in the southern hemisphere, under ESO programmes P095.A-0840, P095.A-0653, and P186.A-0798.
HD 66051: the first eclipsing binary hosting an early-type magnetic star
Kochukhov, O.; Johnston, C.; Alecian, E.; Wade, G. A.
Early-type magnetic stars are rarely found in close binary systems. No such objects were known in eclipsing binaries prior to this study. Here we investigated the eclipsing, spectroscopic double-lined binary HD 66051, which exhibits out-of-eclipse photometric variations suggestive of surface brightness inhomogeneities typical of early-type magnetic stars. Using a new set of high-resolution spectropolarimetric observations, we discovered a weak magnetic field on the primary and found intrinsic, element-dependent variability in its spectral lines. The magnetic field structure of the primary is dominated by a nearly axisymmetric dipolar component with a polar field strength Bd ≈ 600 G and an inclination with respect to the rotation axis of βd = 13°. A weaker quadrupolar component is also likely to be present. We combined the radial velocity measurements derived from our spectra with archival optical photometry to determine fundamental masses (3.16 and 1.75 M⊙) and radii (2.78 and 1.39 R⊙) with a 1-3% precision. We also obtained a refined estimate of the effective temperatures (13000 and 9000 K) and studied chemical abundances for both components with the help of disentangled spectra. We demonstrate that the primary component of HD 66051 is a typical late-B magnetic chemically peculiar star with a non-uniform surface chemical abundance distribution. It is not an HgMn-type star as suggested by recent studies. The secondary is a metallic-line star showing neither a strong, global magnetic field nor intrinsic spectral variability. Fundamental parameters provided by our work for this interesting system open unique possibilities for probing interior structure, studying atomic diffusion, and constraining binary star evolution.
The Abundances of the Iron Group Elements in Early B Stars in the Magellanic Clouds
Peters, C.
FUSE observations of four sharp-lined early B main-sequence band stars in the Magellanic Clouds will be carried through to determine the abundances of the heavy elements, especially those of the Fe group. The FUSE spectral region contains numerous Fe III lines, including the resonance multiplet (UV1) near 1130 A that is excellent for abundance determinations and two strong multiplets of V III, an ion that does not produce measurable lines longward of 1200 A in metal-deficient stars. In addition there are several measurable lines from Cr III and Mn III. Although abundances of the Fe-peak elements are of interest because they are important for assessing opacities for stellar evolution calculations and the validity of theoretical calculations of explosive nucleosynthesis, ground-based studies do not yield this information because measurable lines from these species, except for a few Fe III lines, are found only in the UV spectral region. The abundances of heavy elements provide information on the production of such elements in previous generations of stars. From FUSE data obtained in Cycle 3 we are determining the abundances of the Fe group elements in two sharp-lined early B stars in the SMC (AV 304, a field star, and NGC346-637, a star in a mini-starburst cluster). This project will allow one to compare the abundances in AV 304 and NGC346-637 with those in the LMC and other regions in the SMC and look for asymmetry in heavy element production in the Magellanic Clouds.
Two-dimensional models of fast rotating early-type stars
Rieutord, Michel
Rotation has now become an unavoidable parameter of stellar models, but for most massive or intermediate-mass stars rotation is fast, at least of a significant fraction of the critical angular velocity. Current spherically symmetric models try to cope with this feature of the stars using various approximations, like for instance the so-called shellular rotation usually accompanied with a diffusion that is meant to represent the mixing induced by rotationally generated flows. Such approximations may be justified in the limit of slow rotation where anisotropies and associated flows are weak. However, when rotation is fast, say larger than 50% of the critical velocities the use of a spherically symmetric 1D-model is doubtful. This is not only because of the centrifugal flattening of the star, but also because of the flows that are induced by the baroclinic torque that naturally appears in the radiative envelope of an early-type (rotating) star. These flows face the cylindrical symmetry of the Coriolis force and the spheroidal symmetry of the effective gravity.In this talk I shall present the latest results of the ESTER project that has taken up the challenge of making two-dimensional (axisymmetric) models of stars rotating at any rotation rate. In particular, I will focus on main sequence massive and intermediate-mass stars. I'll show what should be expected in such stars as far as the differential rotation and the associated meridional circulation are concerned, notably the emergence of a Stewartson layer along the tangential cylinder of the core. I'll also indicate what may be inferred about the evolution of an intermediate-mass star at constant angular momentum and how Be stars may form. I shall finally give some comparisons between models and observations of the gravity darkening on some nearby fast rotators as it has been derived from interferometric observations. In passing, I'll also discuss how 2D models can help to recover the fundamental parameters of a star.
Colliding winds from early-type stars in binary systems
Stevens, Ian R.; Blondin, John M.; Pollock, A. M. T.
The dynamics of the wind and shock structure formed by the wind collision in early-type binary systems is examined by means of a 2D hydrodynamics code, which self-consistently accounts for radiative cooling, and represents a significant improvement over previous attempts to model these systems. The X-ray luminosity and spectra of the shock-heated region, accounting for wind attenuation and the influence of different abundances on the resultant level and spectra of X-ray emission are calculated. A variety of dynamical instabilities that are found to dominate the intershock region is examined. These instabilities are found to be particularly important when postshock material is able to cool. These instabilities disrupt the postshock flow and add a time variability of order 10 percent to the X-ray luminosity. The X-ray spectrum of these systems is found to vary with the nuclear abundances of winds. These theoretical models are used to study several massive binary systems, in particular V444 Cyg and HD 193793.
Reversal of Fortune: Increased Star Formation Efficiencies in the Early Histories of Dwarf Galaxies?
Madau, Piero; Weisz, Daniel R.; Conroy, Charlie
On dwarf galaxy scales, the different shapes of the galaxy stellar mass function and the dark halo mass function require a star-formation efficiency (SFE) in these systems that is currently more than 1 dex lower than that of Milky Way-size halos. Here, we argue that this trend may actually be reversed at high redshift. Specifically, by combining the resolved star-formation histories of nearby isolated dwarfs with the simulated mass-growth rates of dark matter halos, we show that the assembly of these systems occurs in two phases: (1) an early, fast halo accretion phase with a rapidly deepening potential well, characterized by a high SFE; and (2) a late, slow halo accretion phase where, perhaps as a consequence of reionization, the SFE is low. Nearby dwarfs have more old stars than predicted by assuming a constant or decreasing SFE with redshift, a behavior that appears to deviate qualitatively from the trends seen among more massive systems. Taken at face value, the data suggest that at sufficiently early epochs, dwarf galaxy halos above the atomic cooling mass limit can be among the most efficient sites of star formation in the universe.
Green Peas emit X-rays: Extreme Star Formation in Early Universe Analog Galaxies
Brorby, Matthew; Kaaret, Philip
Luminous compact galaxies (LCGs), Lyman Alpha Emitters (LAEs), and Lyman Break Analog galaxies (LBAs) are all used as proxies for star-forming galaxies in the early Universe (z ≥ 6). The X-ray emission from such galaxies has been found to be elevated compared to other star-forming galaxies in our local Universe. It has been suggested that this may be due to the lower metallicity seen in these proxies to high-redshift galaxies and the elevated X-ray emission may affect the heating and Reionization evolution of the early Universe. Our previous studies have suggested the existence of an LX-SFR-metallicity plane for all star-forming galaxies. We present these results in the context of our newest Joint Chandra/HST study containing the first X-ray detection of the Green Pea galaxies, a population of compact starburst galaxies discovered by volunteers in the Galaxy Zoo Project (Cardamone+2009). The galaxies were given the name Green Peas due to their compact size and green appearance in the gri composite images from SDSS. The green color is caused by a strong [OIII]λ5007Å emission line, an indicator of recent star formation. We observed a few of the most promising candidates with joint Chandra/HST observation and discuss our findings here.
VizieR Online Data Catalog: Magnetic early B-type stars. I. (Shultz+, 2018)
Shultz, M.; Wade, G. A.; Rivinius, Th.; Neiner, C.; Alecian, E.; Bohlender, D.; Monin, D.; Sikora, J.; Mimes Collaboration; Binamics Collaboration
Longitudinal magnetic field measurements of early B-type stars derived from 1) least-squares deconvolution profiles extracted from high-resolution spectropolarimetric data (ESPaDOnS, Narval, HARPSpol), using masks consisting of metallic lines, metallic + He lines, individual chemical elements, as well as single-line H measurements; and 2) from single-line low-resolution spectropolarimetric observations with dimaPol. (3 data files).
Colliding stellar winds in O-type close binary systems
Gies, Douglas R.
A study of the stellar wind properties of O-type close binary systems is presented. The main objective of this program was to search for colliding winds in four systems, AO Cas, iota Ori, Plaskett's star, and 29 UW CMa, through an examination of high dispersion UV spectra from IUE and optical spectra of the H alpha and He I lambda 6678 emission lines.
Measurements of eight early-type stars angular diameters using VEGA/CHARA interferometer
Challouf, M.; Nardetto, N.; Mourard, D.; Aroui, H.; Delaa, O.
The surface brightness color (SBC) relation is an important tool to derive the distance of extragalatic eclipsing binaries. We determined the uniform disc angular diameter of the eight following early-type stars using VEGA/CHARA interferometric observations: θ_{UD}[δ Cyg] = 0.766 ± 0.047 mas, θ_{UD}[γ Lyr] = 0.742& ± 0.010 mas, θ_{UD}[γ Ori] = 0.701 ± 0.005 mas, θ_{UD}[ζ Peg] = 0.539 ± 0.009 mas, θ_{UD}[λ Aql] = 0.529 ± 0.003 mas, θ_{UD}[ζ Per] = 0.531 ± 0.007 mas, θ_{UD}[ι Her] = 0.304 ± 0.010 mas and θ_{UD}[8 Cyg] = 0.229 ± 0.011 mas (by extending V-K range from -0.76 to 0.02) with typical precision of about 1.5%. By combining these data with previous angular diameter determinations available in the literature, Challouf et al. (2014) provide for the very first time a SBC relation for early-type stars (-1≤V-K≤0) with a precision of about 0.16 magnitude or 7% in term of angular diameter (when using this SBC relation to derive the angular diameter of early-type stars).
Early type galaxies: Mapping out the two-dimensional space of galaxy star formation histories
Graves, Genevieve J.
Early type galaxies form a multi-parameter family, as evidenced by the two- dimensional (2-D) Fundamental Plane relationship. However, their star formation histories are often treated as a one-dimensional mass sequence. This dissertation presents a systematic study of the relationship between the multi- parameter structural properties of early type galaxies and their star formation histoires. We demonstrate that the stellar populations of early type galaxies span a 2-D space, which means that their star formation histories form a two- parameter family. This 2-D family is then mapped onto several familiar early type galaxy scaling relations, including the color-magnitude relation, the Fundamental Plane, and a cross-section through the Fundamental Plane. We find that the stellar population properties, and therefore the star formation histories of early type galaxies depend most strongly on galaxy velocity dispersion (s), rather than on luminosity ( L ), stellar mass ( M [low *] ), or dynamical mass ( M dyn ). Interestingly, stellar populations are independent of the radius ( R e ) of the galaxies. At fixed s, they show correlated residuals through the thickness of the Fundamental Plane (FP) in the surface-brightness ( I e ) dimension, such that low-surface-brightness galaxies are older, less metal-enriched, and more enhanced in Mg relative to Fe than their counterparts at the same s and R e on the FP midplane. Similarly, high- surface-brightness galaxies are younger, more metal-rich, and less Mg-enhanced than their counterparts on the FP midplane. These differences suggest that the duration of star formation varies through the thickness of the FP. If the dynamical mass-to-light ratios of early type galaxies ( M dyn /L ) were constant for all such galaxies, the FP would be equivalent to the plane predicted by the virial relation. However, the observed FP does not exactly match the virial plane. The FP is tilted from the virial plane, indicating that M dyn /L varies
The peculiar, luminous early-type emission line stars of the Magellanic clouds: A preliminary taxonomy
Shore, S. N.; Sanduleak, N.
A sample of some 20 early type emission supergiants in the Magellanic clouds was observed with both the SWP and LWR low resolution mode of IUE. All stars have strong H-emission, some showing P-Cygni structure as well with HeI, HeII, FeII and other ions also showing strong emission. It is found that the stars fall into three distinct groups on the basis of the HeII/HeI and HeI/HI strengths: (1) HeII strong, HeI, HI; (2) HeII absent, HeI, HI strong; (3) HeI absent, HI, FeII, FeII, strong in addition to low excitation ions. The two most extreme emission line stars found in the Clouds S 134/LMC and S 18/SMC are discussed. Results for the 2200A feature in these supergiants, and evidence for shells around the most luminous stars in the clouds are also described.
STAR - Research Experiences at National Laboratory Facilities for Pre-Service and Early Career Teachers
Keller, J. M.; Rebar, B.; Buxner, S.
The STEM Teacher and Researcher (STAR) Program provides pre-service and beginning teachers the opportunity to develop identity as both teachers and researchers early in their careers. Founded and implemented by the Center for Excellence in Science and Mathematics Education (CESaME) at California Polytechnic State University on behalf of the California State University (CSU) system, STAR provides cutting edge research experiences and career development for students affiliated with the CSU system. Over the past three summers, STAR has also partnered with the NSF Robert Noyce Teacher Scholarship Program to include Noyce Scholars from across the country. Key experiences are one to three summers of paid research experience at federal research facilities associated with the Department of Energy (DOE), National Aeronautics and Space Administration (NASA), National Oceanic and Atmospheric Association (NOAA), and the National Optical Astronomy Observatory (NOAO). Anchoring beginning teachers in the research community enhances participant understanding of what it means to be both researchers and effective teachers. Since its inception in 2007, the STAR Program has partnered with 15 national lab facilities to provide 290 research experiences to 230 participants. Several of the 68 STAR Fellows participating in the program during Summer 2012 have submitted abstracts to the Fall AGU Meeting. Through continued partnership with the Noyce Scholar Program and contributions from outside funding sources, the CSU is committed to sustaining the STAR Program in its efforts to significantly impact teacher preparation. Evaluation results from the program continue to indicate program effectiveness in recruiting high quality science and math majors into the teaching profession and impacting their attitudes and beliefs towards the nature of science and teaching through inquiry. Additionally, surveys and interviews are being conducted of participants who are now teaching in the classroom as
An XMM Investigation of Non-Thermal Phenomena in the Winds of Early-Type Stars
Waldron, Wayne L.; Mushotzky, Richard (Technical Monitor)
The X-ray emission from early-type stars is believed to arise from a stellar wind distribution of shocks. Hence, X-ray analyses of these stars must include the effects of stellar wind X-ray absorption, which, in general dominates the ISM absorption. Although the absorption cross sections for the wind and ISM are essentially identical above 1 keV, there is substantial differences below 1 keV. Typically, if one only uses ISM cross sections to obtain fits to X-ray spectra, the fits usually indicate a model deficiency at energies below 1 keV which is attributed to the large increase in ISM cross sections at these energies. This deficiency can be eliminated by using stellar wind absorption models with a fixed ISM component. Since all early-type stars have substantial X-ray emission below 1 keV, than inclusion of wind absorption has proven to be a critical component in fitting X-ray spectra at low energies, verifying that these X-rays are indeed arising from within the stellar wind.
New radio detections of early-type pre-main-sequence stars
Skinner, Stephen L.; Brown, Alexander; Linsky, Jeffrey L.
Results of VLA radio continuum observations of 13 early-type pre-main-sequence stars selected from the 1984 catalog of Finkenzeller and Mundt are presented. The stars HD 259431 and MWC 1080 were detected at 3.6 cm, while HD 200775 and TY CrA were detected at both 3.6 and 6 cm. The flux density of HD 200775 has a frequency dependence consistent with the behavior expected for free-free emission originating in a fully ionized wind. However, an observation in A configuration suggests that the source geometry may not be spherically symmetric. In contrast, the spectral index of TY CrA is negative with a flux behavior implying nonthermal emission. The physical mechanism responsible for the nonthermal emission has not yet been identified, although gyrosynchrotron and synchrotron processes cannot be ruled out.
Exploring the dusty star-formation in the early Universe using intensity mapping
Lagache, Guilaine
In the last decade, it has become clear that the dust-enshrouded star formation contributes significantly to early galaxy evolution. Detection of dust is therefore essential in determining the properties of galaxies in the high-redshift universe. This requires observations at the (sub-)millimeter wavelengths. Unfortunately, sensitivity and background confusion of single dish observations on the one hand, and mapping efficiency of interferometers on the other hand, pose unique challenges to observers. One promising route to overcome these difficulties is intensity mapping of fluctuations which exploits the confusion-limited regime and measures the collective light emission from all sources, including unresolved faint galaxies. We discuss in this contribution how 2D and 3D intensity mapping can measure the dusty star formation at high redshift, through the Cosmic Infrared Background (2D) and [CII] fine structure transition (3D) anisotropies.
The star formation history of early-type galaxies as a function of mass and environment
Clemens, M. S.; Bressan, A.; Nikolic, B.; Alexander, P.; Annibali, F.; Rampazzo, R.
Using the third data release of the Sloan Digital Sky Survey (SDSS), we have rigorously defined a volume-limited sample of early-type galaxies in the redshift range 0.005 < z <= 0.1. We have defined the density of the local environment for each galaxy using a method which takes account of the redshift bias introduced by survey boundaries if traditional methods are used. At luminosities greater than our absolute r-band magnitude cut-off of -20.45, the mean density of environment shows no trend with redshift. We calculate the Lick indices for the entire sample and correct for aperture effects and velocity dispersion in a model-independent way. Although we find no dependence of redshift or luminosity on environment, we do find that the mean velocity dispersion, σ, of early-type galaxies in dense environments tends to be higher than in low-density environments. Taking account of this effect, we find that several indices show small but very significant trends with environment that are not the result of the correlation between indices and velocity dispersion. The statistical significance of the data is sufficiently high to reveal that models accounting only for α-enhancement struggle to produce a consistent picture of age and metallicity of the sample galaxies, whereas a model that also includes carbon enhancement fares much better. We find that early-type galaxies in the field are younger than those in environments typical of clusters but that neither metallicity, α-enhancement nor carbon enhancement are influenced by the environment. The youngest early-type galaxies in both field and cluster environments are those with the lowest σ. However, there is some evidence that the objects with the largest σ are slightly younger, especially in denser environments. Independent of environment both the metallicity and α-enhancement grow monotonically with σ. This suggests that the typical length of the star formation episodes which formed the stars of early-type galaxies
Water on the Early M Supergiant Stars α Orionis and μ Cephei
Tsuji, T.
We reanalyze the spectra of α Ori (M2 Iab) and μ Cep (M2 Ia) observed with the balloon-borne telescope Stratoscope II more than 35 years ago, and we confirm the presence of water in these early M supergiant stars. This identification was first proposed by the Stratoscope observers themselves (Woolf, Schwarzschild, and Rose in 1964; and Danielson, Woolf, and Gaustad in 1965), but this important discovery was overlooked for a long time without any follow-up observation. Consequently, this finding has so far had little influence on the theory of the atmosphere of red supergiant stars. A reason for this may be due to an early criticism by Wing and Spinrad, who suggested CN instead of H2O for the spectral features observed by Stratoscope II. This alternative proposition has more easily been accepted since CN has widely been observed from the Sun to red supergiants, while H2O has been observed only in very cool stars such as Mira variables. In fact, we confirm that the self-consistent photospheric model of the early M supergiants shows CN bands but no H2O band in the near-infrared. Nevertheless, we find that the contribution of CN is only minor and that H2O should be the dominant absorber for the 1.4 and 1.9 μm features on the Stratoscope spectra of α Ori and μ Cep, a conclusion opposite to that of Wing and Spinrad. The observed spectra can best be interpreted by the water gas with the column density of the order of 1020 cm-2 and temperature about 1500+/-500 K, but they cannot be originating in the photosphere. We suggest a possible presence of a gaseous component not as hot as the chromosphere but warmer than the cool expanding envelope. On the other hand, we notice that the mid-infrared pure-rotation lines of H2O recently discovered on Betelgeuse (α Ori) and Antares (α Sco) by Jennings and Sada may partly be originating in the photosphere, even though the larger part should again be nonphotospheric in origin. Thus, the presence of water possibly originating in
Dust-obscured star-forming galaxies in the early universe
Wilkins, Stephen M.; Feng, Yu; Di Matteo, Tiziana; Croft, Rupert; Lovell, Christopher C.; Thomas, Peter
Motivated by recent observational constraints on dust reprocessed emission in star-forming galaxies at z ∼ 6 and above, we use the very large cosmological hydrodynamical simulation BLUETIDES to explore predictions for the amount of dust-obscured star formation in the early Universe (z > 8). BLUETIDES matches current observational constraints on both the UV luminosity function and galaxy stellar mass function and predicts that approximately 90 per cent of the star formation in high-mass (M* > 1010 M⊙) galaxies at z = 8 is already obscured by dust. The relationship between dust attenuation and stellar mass predicted by BLUETIDES is consistent with that observed at lower redshift. However, observations of several individual objects at z > 6 are discrepant with the predictions, though it is possible that their uncertainties may have been underestimated. We find that the predicted surface density of z ≥ 8 submm sources is below that accessible to current Herschel, SCUBA-2 and Atacama Large Millimetre Array (ALMA) submm surveys. However, as ALMA continues to accrue an additional surface area the population of z > 8 dust-obscured galaxies may become accessible in the near future.
The very high rotators in the late-B and early-A stars: Shell stars with Si IV and C IV features the case of HD 119921
Freireferrero, R.; Bruhweiler, Frederick C.; Grady, C. A.
Study of several stars in the late B and early A spectral types shows that very high rotators are associated with shell characteristics (sometimes not detected at all in the visible spectra) and also with C IV and some Si IV spectral absorption features which can be explained by circumstellar phenomena superimposed over stellar metallic blends. These particularities are evidenced by comparison with other spectra of low and high rotators in the same spectral range. HD 119921, a star with similar characteristics to the other ones of the sample, is given special attention. A possible scenario is suggested to explain the observed superionization features.
Star formation in early-type galaxies: the role of stellar winds and kinematics.
Pellegrini, Silvia; Negri, Andrea; Ciotti, Luca
Early-Type galaxies (ETGs) host a hot ISM produced mainly by stellar winds, and heated by Type Ia supernovae (SNIa) and the thermalization of stellar motions. Recent high resolution 2D hydrodynamical simulations (Negri et al. 2014) showed that ordered rotation in the stellar component alters significantly the evolution of the hot ISM, and results in the formation of a centrifugally supported cold equatorial disc. This agrees well with the recent evidence that approximately 50% of massive ETGs host significant quantities of cold gas (Morganti et al. 2006; Young et al. 2014), often in settled configurations, sharing the same kinematics of the stars. In particular, in a systematic investigation of the ATLAS3D sample, the most massive fast-rotating ETGs always have kinematically aligned gas, which suggests an internal origin for it, and molecular gas is detected only in fast rotators (Davis et al. 2011). The observed cold gas seems also to provide material for low level star formation (SF) activity (Combes et al. 2007, Davis et al. 2014). Interestingly, in the ATLAS3D sample, SF and young stellar populations are detected only in fast rotators (Sarzi et al. 2013). In a recent work we investigated whether and how SF takes place in the cold gas disc typically produced in rotating ETGs by our previous 2D simulations, by adding to them the possibility for the gas to form stars (Negri et al. 2015). We also inserted the injection of mass, momentum and energy appropriate for the newly (and continuously) forming stellar population. We found that subsequent generations of stars are formed, and that most of the extended and massive cold disc is consumed by this process, leaving at the present epoch cold gas masses that compare well with those observed. The mass in secondary generations of stars resides mostly in a disc, and could be related to a younger, more metal rich disky stellar component indeed observed in fast rotator ETGs (Cappellari et al. 2013). Most of the mass in
Further RIOTS4 Characterization of Field OB Stars in the SMC
Oey, M. S.; Barnes, Jesse R.; Paggeot, Kevin J.; Dorigo Jones, John; Castro, Norberto; Simon-Diaz, Sergio; Kratter, Kaitlin M.; Moe, Maxwell; Szymanski, Michal
We present recent results from the Runaways and O-Type Star Spectroscopic Survey of the SMC (RIOTS4), a survey quantifying properties of the field OB stars in the Small Magellanic Cloud (SMC). Based on PSF-fitting photometry and astrometry of OGLE-III I-band images, we quantify the degree of isolation for the target OB stars, classifying them as "tip-of-the-iceberg" stars accompanied by small, sparse, clusters; or as true, isolated field stars. Many of these field stars must be runaways, which we evaluate using GAIA DR2 proper motions. We measure v sin i using the IACOB code Fourier analysis, finding that the bimodal distribution of projected rotation velocities is less pronounced for O stars than early B stars. We examine rotation in relation to relative isolation and runaway status.
Chromospherically active stars. IV - HD 178450 = V478 Lyr: An early-type BY Draconis type binary
Fekel, Francis C.
It is shown that the variable star HD 178450 = V478 Lyr is a chromospherically active G8 V single-lined spectroscopic binary with a period of 2.130514 days. This star is characterized by strong UV emission features and a filled-in H-alpha absorption line which is variable in strength. Classified as an early-type BY Draconis system, it is similar to the BY Dra star HD 175742 = V775 Her. The unseen secondary of HD 178450 has a mass of about 0.3 solar masses and is believed to be an M2-M3 dwarf.
Identifying Massive Runaway Stars by Detecting Infrared Bowshock Nebula: Four OB Stars and a New Massive Early-B Binary System
Sorber, Rebecca L.; Rebecca L. Sorber, Henry A. Kobulnicky, Daniel A. Dale, Matthew S. Povich, William T. Chick, Heather N. Wernke, Julian E. Andrews, Stephan Munari, Grace M. Olivier, Danielle Schurhammer
Though the main sequence evolution of OB type stars is relatively well known, the mass loss rates for these stars are still highly uncertain. Some OB stars are gravitationally ejected from their birth sites, traveling at speeds of 30 km/s or more which results in a prominent bowshock nebulae. We identified OB bowshock candidates at low Galactic latitudes by visual inspection of the Wide-field Infrared Survey Explorer (WISE) 22-micron images. Each candidate was observed using the Longslit Spectrograph at the Wyoming Infrared Observatory (WIRO) 2.3 meter telescope. We present here the results from observing four such candidates, and all four are confirmed as early type stars: GO92.3191+0.0591 (B1V) (aka ALS11826), GO86.551014-1.0873935 (B2V; a probable short-period binary), G076.6921-2.4071 (B5V), and G075.5711-0.2558 (B0V) (aka HD 194303). These results enlarge the sample of candidate runaway massive stars hosting bowshocks and provide a promising sample of such objects for studying stellar mass loss. This work is supported by the National Science Foundation Grants AST-1063146 (REU), AST-1411851 (RUI), and AST-1412845.
Early Results from Star Date: M83 - A Citizen Science Project to Age Date Star Clusters in the Southern Pinwheel Galaxy
Heartley, Jeremy; Whitmore, B. C.; Blair, W. P.; Christian, C. A.; Donaldson, T.; Hammer, D.; Smith, S.; Viana, A.
The M83 Citizen Science Project is a collaborative effort currently in development between the Space Telescope Science Institute (STScI) and Zooniverse under the guidance of Dr. Brad Whitmore as part of Cy 19 proposal 12513 (PI - Dr. William Blair). This unique citizen science project will allow users to analyze individual star clusters within The Southern Pinwheel Galaxy, M83. The project will show users color-composite images taken with Wide Field Camera 3 (WFC3) aboard the Hubble Space Telescope (HST) and ask them to estimate the age of the star cluster. Through a multistage process, the project will educate and familiarize the user with the appearance of each age category based on the presence and shape of H-alpha emission, degree of resolution of the individual stars, and color of the cluster. (Whitmore et al. 2011). Additionally, the project will involve the actual measurement of the star cluster and H-alpha cloud radii to be used for further assessment and reinforcement of age. The data from this project and the statistics it yields will quantify these ages which can then be used to inform the debate between universal and environmental models of star cluster formation and destruction in galaxies. The tentative launch date is December 2013, therefore early results should be available at the time of the conference.
Chemical characterization of the early evolutionary phases of high-mass star-forming regions
Gerner, Thomas
The formation of high-mass stars is a very complex process and up to date no comprehensive theory about it exists. This thesis studies the early stages of high-mass star-forming regions and employs astrochemistry as a tool to probe their different physical conditions. We split the evolutionary sequence into four observationally motivated stages that are based on a classification proposed in the literature. The sequence is characterized by an increase of the temperatures and densities that strongly influences the chemistry in the different stages. We observed a sample of 59 high-mass star-forming regions that cover the whole sequence and statistically characterized the chemical compositions of the different stages. We determined average column densities of 18 different molecular species and found generally increasing abundances with stage. We fitted them for each stage with a 1D model, such that the result of the best fit to the previous stage was used as new input for the following. This is a unique approach and allowed us to infer physical properties like the temperature and density structure and yielded a typical chemical lifetime for the high-mass star-formation process of 1e5 years. The 18 analyzed molecular species also included four deuterated molecules whose chemistry is particularly sensitive to thermal history and thus is a promising tool to infer chemical ages. We found decreasing trends of the D/H ratios with evolutionary stage for 3 of the 4 molecular species and that the D/H ratio depends more on the fraction of warm and cold gas than on the total amount of gas. That indicates different chemical pathways for the different molecules and confirms the potential use of deuterated species as chemical age indicators. In addition, we mapped a low-mass star forming region in order to study the cosmic ray ionization rate, which is an important parameter in chemical models. While in chemical models it is commonly fixed, we found that it ! strongly varies with
Early spectra of the gravitational wave source GW170817: Evolution of a neutron star merger.
Shappee, B J; Simon, J D; Drout, M R; Piro, A L; Morrell, N; Prieto, J L; Kasen, D; Holoien, T W-S; Kollmeier, J A; Kelson, D D; Coulter, D A; Foley, R J; Kilpatrick, C D; Siebert, M R; Madore, B F; Murguia-Berthier, A; Pan, Y-C; Prochaska, J X; Ramirez-Ruiz, E; Rest, A; Adams, C; Alatalo, K; Bañados, E; Baughman, J; Bernstein, R A; Bitsakis, T; Boutsia, K; Bravo, J R; Di Mille, F; Higgs, C R; Ji, A P; Maravelias, G; Marshall, J L; Placco, V M; Prieto, G; Wan, Z
On 17 August 2017, Swope Supernova Survey 2017a (SSS17a) was discovered as the optical counterpart of the binary neutron star gravitational wave event GW170817. We report time-series spectroscopy of SSS17a from 11.75 hours until 8.5 days after the merger. Over the first hour of observations, the ejecta rapidly expanded and cooled. Applying blackbody fits to the spectra, we measured the photosphere cooling from [Formula: see text] to [Formula: see text] kelvin, and determined a photospheric velocity of roughly 30% of the speed of light. The spectra of SSS17a began displaying broad features after 1.46 days and evolved qualitatively over each subsequent day, with distinct blue (early-time) and red (late-time) components. The late-time component is consistent with theoretical models of r-process-enriched neutron star ejecta, whereas the blue component requires high-velocity, lanthanide-free material. Copyright © 2017, American Association for the Advancement of Science.
Long-orbital-period Prepolars Containing Early K-type Donor Stars. Bottleneck Accretion Mechanism in Action
Tovmassian, G.; González–Buitrago, D.; Zharikov, S.; Reichart, D. E.; Haislip, J. B.; Ivarsen, K. M.; LaCluyze, A. P.; Moore, J. P.; Miroshnichenko, A. S.
We studied two objects identified as cataclysmic variables (CVs) with periods exceeding the natural boundary for Roche-lobe-filling zero-age main sequence (ZAMS) secondary stars. We present observational results for V1082 Sgr with a 20.82 hr orbital period, an object that shows a low luminosity state when its flux is totally dominated by a chromospherically active K star with no signs of ongoing accretion. Frequent accretion shutoffs, together with characteristics of emission lines in a high state, indicate that this binary system is probably detached, and the accretion of matter on the magnetic white dwarf takes place through stellar wind from the active donor star via coupled magnetic fields. Its observational characteristics are surprisingly similar to V479 And, a 14.5 hr binary system. They both have early K-type stars as donor stars. We argue that, similar to the shorter-period prepolars containing M dwarfs, these are detached binaries with strong magnetic components. Their magnetic fields are coupled, allowing enhanced stellar wind from the K star to be captured and channeled through the bottleneck connecting the two stars onto the white dwarf's magnetic pole, mimicking a magnetic CV. Hence, they become interactive binaries before they reach contact. This will help to explain an unexpected lack of systems possessing white dwarfs with strong magnetic fields among detached white+red dwarf systems.
The ATLAS3D Project - XXX. Star formation histories and stellar population scaling relations of early-type galaxies
McDermid, Richard M.; Alatalo, Katherine; Blitz, Leo; Bournaud, Frédéric; Bureau, Martin; Cappellari, Michele; Crocker, Alison F.; Davies, Roger L.; Davis, Timothy A.; de Zeeuw, P. T.; Duc, Pierre-Alain; Emsellem, Eric; Khochfar, Sadegh; Krajnović, Davor; Kuntschner, Harald; Morganti, Raffaella; Naab, Thorsten; Oosterloo, Tom; Sarzi, Marc; Scott, Nicholas; Serra, Paolo; Weijmans, Anne-Marie; Young, Lisa M.
We present the stellar population content of early-type galaxies from the ATLAS3D survey. Using spectra integrated within apertures covering up to one effective radius, we apply two methods: one based on measuring line-strength indices and applying single stellar population (SSP) models to derive SSP-equivalent values of stellar age, metallicity, and alpha enhancement; and one based on spectral fitting to derive non-parametric star formation histories, mass-weighted average values of age, metallicity, and half-mass formation time-scales. Using homogeneously derived effective radii and dynamically determined galaxy masses, we present the distribution of stellar population parameters on the Mass Plane (MJAM, σe, R^maj_e), showing that at fixed mass, compact early-type galaxies are on average older, more metal-rich, and more alpha-enhanced than their larger counterparts. From non-parametric star formation histories, we find that the duration of star formation is systematically more extended in lower mass objects. Assuming that our sample represents most of the stellar content of today's local Universe, approximately 50 per cent of all stars formed within the first 2 Gyr following the big bang. Most of these stars reside today in the most massive galaxies (>1010.5 M⊙), which themselves formed 90 per cent of their stars by z ˜ 2. The lower mass objects, in contrast, have formed barely half their stars in this time interval. Stellar population properties are independent of environment over two orders of magnitude in local density, varying only with galaxy mass. In the highest density regions of our volume (dominated by the Virgo cluster), galaxies are older, alpha-enhanced, and have shorter star formation histories with respect to lower density regions.
Low-mass galaxy assembly in simulations: regulation of early star formation by radiation from massive stars
Trujillo-Gomez, Sebastian; Klypin, Anatoly; Colín, Pedro; Ceverino, Daniel; Arraki, Kenza S.; Primack, Joel
Despite recent success in forming realistic present-day galaxies, simulations still form the bulk of their stars earlier than observations indicate. We investigate the process of stellar mass assembly in low-mass field galaxies, a dwarf and a typical spiral, focusing on the effects of radiation from young stellar clusters on the star formation (SF) histories. We implement a novel model of SF with a deterministic low efficiency per free-fall time, as observed in molecular clouds. Stellar feedback is based on observations of star-forming regions, and includes radiation pressure from massive stars, photoheating in H II regions, supernovae and stellar winds. We find that stellar radiation has a strong effect on the formation of low-mass galaxies, especially at z > 1, where it efficiently suppresses SF by dispersing cold and dense gas, preventing runaway growth of the stellar component. This behaviour is evident in a variety of observations but had so far eluded analytical and numerical models without radiation feedback. Compared to supernovae alone, radiation feedback reduces the SF rate by a factor of ˜100 at z ≲ 2, yielding rising SF histories which reproduce recent observations of Local Group dwarfs. Stellar radiation also produces bulgeless spiral galaxies and may be responsible for excess thickening of the stellar disc. The galaxies also feature rotation curves and baryon fractions in excellent agreement with current data. Lastly, the dwarf galaxy shows a very slow reduction of the central dark matter density caused by radiation feedback over the last ˜7 Gyr of cosmic evolution.
L(alpha)-induced two-photon absorption of visible light emitted from an O-type star by H2(+) ions located near the surface of the Stromgren sphere surrounding the star: A possible explanation for the diffuse interstellar absorption bands (DIDs)
Glownia, James H.; Sorokin, Peter P.
In this paper, a new model is proposed to account for the DIB's (Diffuse Interstellar Bands). In this model, the DIB's result from a non-linear effect: resonantly-enhanced two-photon absorption of H(2+) ions located near the surface of the Stromgren sphere that surrounds an O- or B- type star. The strong light that is required to 'drive' the two-photon transition is provided by L(alpha) light emerging from the Stromgren sphere that bounds the H II region surrounding the star. A value of approximately 100 micro W/sq cm is estimated for the L(alpha) flux at the Stromgren radius, R(s), of a strong (O5) star. It is shown that a c.w. L(alpha) flux of this intensity should be sufficient to induce a few percent absorption for visible light radiated by the same star at a frequency (omega2) that completes an allowed two-photon transition, provided (1) the L(alpha) radiation happens to be nearly resonant with the frequency of a fully-allowed absorber transition that effectively represents the first step in the two-photon transition, and (2) an effective column density approximately 10(sup18)/sq cm of the absorber is present near the Stromgren sphere radius, R(sub s).
Embedded Filaments in IRAS 05463+2652: Early Stage of Fragmentation and Star Formation Activities
Dewangan, L. K.; Devaraj, R.; Baug, T.; Ojha, D. K.
We present a multiwavelength data analysis of IRAS 05463+2652 (hereafter I05463+2652) to study star formation mechanisms. A shell-like structure around I05463+2652 is evident in the Herschel column density map, which is not associated with any ionized emission. Based on the Herschel submillimeter images, several parsec-scale filaments (including two elongated filaments, "s-fl� and "nw-fl� having lengths of ˜6.4 and ˜8.8 pc, respectively) are investigated in the I05463+2652 site. The Herschel temperature map depicts all these features in a temperature range of ˜11-13 K. 39 clumps are identified and have masses between ˜ 70{--}945 {M}⊙ . The majority of clumps (having {M}{clump}≳ 300 {M}⊙ ) are distributed toward the shell-like structure. 175 young stellar objects (YSOs) are selected using the photometric 1-5 μm data and a majority of these YSOs are distributed toward the four areas of high column density (≳ 5× {10}21 cm-2 A V ˜ 5.3 mag) in the shell-like structure, where massive clumps and a spatial association with filament(s) are also observed. The knowledge of observed masses per unit length of elongated filaments and critical mass length reveals that they are supercritical. The filament "nw-fl� is fragmented into five clumps (having {M}{clump}˜ 100{--}545 {M}⊙ ) and contains noticeable YSOs, while the other filament "s-fl� is fragmented into two clumps (having {M}{clump}˜ 170{--}215 {M}⊙ ) without YSOs. Together, these observational results favor the role of filaments in the star formation process in I05480+2545. This study also reveals the filament "s-fl,� containing two starless clumps, at an early stage of fragmentation.
Concurrent formation of supermassive stars and globular clusters: implications for early self-enrichment
Gieles, Mark; Charbonnel, Corinne; Krause, Martin G. H.; Hénault-Brunet, Vincent; Agertz, Oscar; Lamers, Henny J. G. L. M.; Bastian, Nathan; Gualandris, Alessia; Zocchi, Alice; Petts, James A.
We present a model for the concurrent formation of globular clusters (GCs) and supermassive stars (SMSs, ≳ 103 M⊙) to address the origin of the HeCNONaMgAl abundance anomalies in GCs. GCs form in converging gas flows and accumulate low-angular momentum gas, which accretes onto protostars. This leads to an adiabatic contraction of the cluster and an increase of the stellar collision rate. A SMS can form via runaway collisions if the cluster reaches sufficiently high density before two-body relaxation halts the contraction. This condition is met if the number of stars ≳ 106 and the gas accretion rate ≳ 105 M⊙/Myr, reminiscent of GC formation in high gas-density environments, such as - but not restricted to - the early Universe. The strong SMS wind mixes with the inflowing pristine gas, such that the protostars accrete diluted hot-hydrogen burning yields of the SMS. Because of continuous rejuvenation, the amount of processed material liberated by the SMS can be an order of magnitude higher than its maximum mass. This `conveyor-belt' production of hot-hydrogen burning products provides a solution to the mass budget problem that plagues other scenarios. Additionally, the liberated material is mildly enriched in helium and relatively rich in other hot-hydrogen burning products, in agreement with abundances of GCs today. Finally, we find a super-linear scaling between the amount of processed material and cluster mass, providing an explanation for the observed increase of the fraction of processed material with GC mass. We discuss open questions of this new GC enrichment scenario and propose observational tests.
The Abundances of the Fe Group Elements in Early B Stars in the Magellanic Clouds and Bridge
Peters, Geraldine J.; Adelman, Saul J.
The abundances of three Fe Group elements (V, Cr, and Fe) in 9 early main-sequence band B stars in the LMC, 7 in the SMC , and two in the Magellanic Bridge have been determined from archival FUSE observations and the Hubeny/Lanz NLTE programs TLUSTY/SYNSPEC. Lines from the Fe group elements, except for a few weak multiplets of Fe III, are not observable in the optical spectral region. The best set of lines in the FUSE spectral region are Fe III (UV1), V III 1150 Ã…, and Cr III 1137 Ã…. The abundances of these elements in early B stars are a marker for recent SNe Ia activity, as a single exploding white dwarf can deliver 0.5 solar masses of Ni-56 that decays into Fe to the ISM. The Fe group abundances in an older population of stars primarily reflect SNe II activity, in which a single explosion delivers only 0.07 solar masses of Ni-56 to the ISM (the rest remains trapped in the neutron star). The abundances of the Fe group elements in early B stars not only track SNe Ia activity but are also important for computing evolutionary tracks for massive stars. In general, the Fe abundance relative to the sun's value is comparable to the mean abundances for the lighter elements in the Clouds/Bridge but the values of [V,Cr/Fe]sun are smaller. This presentation will discuss the spatial distribution of the Fe Group elements in the Magellanic Clouds, and compare it with our galaxy in which the abundance of Fe declines with radial distance from the center. Support from NASA grants NAG5-13212, NNX10AD66G, STScI HST-GO-13346.22, and USC's Women in Science and Engineering (WiSE) program is greatly appreciated.
Heavy element synthesis in the oldest stars and the early Universe.
Cowan, John J; Sneden, Christopher
The first stars in the Universe were probably quite different from those born today. Composed almost entirely of hydrogen and helium (plus a tiny trace of lithium), they lacked the heavier elements that determine the formation and evolution of younger stars. Although we cannot observe the very first stars--they died long ago in supernovae explosions--they created heavy elements that were incorporated into the next generation. Here we describe how observations of heavy elements in the oldest surviving stars in our Galaxy's halo help us understand the nature of the first stars--those responsible for the chemical enrichment of our Galaxy and Universe.
A survey of interstellar neutral potassium. I - Abundances and physical conditions in clouds toward 188 early-type stars
Chaffee, F. H., Jr.; White, R. E.
Observations of interstellar absorption in the resonance doublet 7664, 7698 A of neutral potassium toward 188 early-type stars at a spectral resolution of 8 km/s are reported. The 7664 A line is successfully separated from nearly coincident telluric O2 absorption for all but a few of the 165 stars for which K I absorption is detected, making possible an abundance analysis by the doublet ratio method. The relationships between the potassium abundances and other atomic abundances, the abundance of molecular hydrogen, and interstellar reddening are investigated.
Evidence for Different Disk Mass Distributions between Early- and Late-type Be Stars in the BeSOS Survey
Arcos, C.; Kanaan, S.; Curé, M.
The circumstellar disk density distributions for a sample of 63 Be southern stars from the BeSOS survey were found by modeling their H α emission line profiles. These disk densities were used to compute disk masses and disk angular momenta for the sample. Average values for the disk mass are 3.4 × 10{sup −9} and 9.5 × 10{sup −10} M {sub ⋆} for early (B0–B3) and late (B4–B9) spectral types, respectively. We also find that the range of disk angular momentum relative to the star is (150–200) J {sub ⋆}/ M {sub ⋆} and (100–150) J {sub ⋆}/ M {submore » ⋆}, again for early- and late-type Be stars, respectively. The distributions of the disk mass and disk angular momentum are different between early- and late-type Be stars at a 1% level of significance. Finally, we construct the disk mass distribution for the BeSOS sample as a function of spectral type and compare it to the predictions of stellar evolutionary models with rapid rotation. The observed disk masses are typically larger than the theoretical predictions, although the observed spread in disk masses is typically large.« less
Properties of the O-type giants and supergiants in 30 Doradus
Ramírez-Agudelo, O. H.; VFTS Consortium
We discuss the stellar and wind properties of 72 presumably single O-type giants, bright giants, and supergiants in the 30 Doradus region. This sample constitutes the largest and most homogeneous sample of such stars ever analyzed and offers the opportunity to test models describing their main-sequence evolution.
ALE OF TWO CLUSTERS YIELDS SECRETS OF STAR BIRTH IN THE EARLY UNIVERSE
This NASA Hubble Space Telescope (HST) image shows rich detail, previously only seen in neighboring star birth regions, in a pair of star clusters 166,000 light-years away in the Large Magellanic Cloud (LMC), in the southern constellation Doradus. The field of view is 130 light-years across and was taken with the Wide Field Planetary Camera 2. HST's unique capabilities -- ultraviolet sensitivity, ability to see faint stars, and high resolution -- have been utilized fully to identify three separate populations in this concentration of nearly 10,000 stars down to the 25th magnitude (more that twice as many as can be seen over the entire sky with the naked eye on a clear night on Earth). The field of view is only 130 light-years across. Previous observations with ground-based telescopes resolve less than 1,000 stars in the same region. About 60 percent of the stars belong to the dominant yellow cluster called NGC 1850, which is estimated to be 50 million years old. A scattering of white stars in the image are massive stars that are only about 4 million years old and represent about 20 percent of the stars in the image. (The remainder are field stars in the LMC.) Besides being much younger, the white stars are much more loosely distributed than the yellow cluster. The significant difference between the two cluster ages suggests these are two separate star groups that lie along the same line of sight. The younger, more open cluster probably lies 200 light-years beyond the older cluster. If it were in the foreground, then dust contained in the white cluster would obscure stars in the older yellow cluster. To observe two well-defined star populations separated by such a small gap of space is unusual. This juxtaposition suggests that supernova explosions in the older cluster might have triggered the birth of the younger cluster. This color composite image is assembled from exposures taken in ultraviolet, visible, and near-infrared light. Yellow stars correspond to Main
Extended main sequence turnoffs in intermediate-age star clusters: a correlation between turnoff width and early escape velocity
Goudfrooij, Paul; Kozhurina-Platais, Vera; Kalirai, Jason S.
We present a color-magnitude diagram analysis of deep Hubble Space Telescope imaging of a mass-limited sample of 18 intermediate-age (1-2 Gyr old) star clusters in the Magellanic Clouds, including eight clusters for which new data were obtained. We find that all star clusters in our sample feature extended main-sequence turnoff (eMSTO) regions that are wider than can be accounted for by a simple stellar population (including unresolved binary stars). FWHM widths of the MSTOs indicate age spreads of 200-550 Myr. We evaluate the dynamical evolution of clusters with and without initial mass segregation. Our main results are (1) the fractionmore » of red clump (RC) stars in secondary RCs in eMSTO clusters scales with the fraction of MSTO stars having pseudo-ages of ≲1.35 Gyr; (2) the width of the pseudo-age distributions of eMSTO clusters is correlated with their central escape velocity v {sub esc}, both currently and at an age of 10 Myr. We find that these two results are unlikely to be reproduced by the effects of interactive binary stars or a range of stellar rotation velocities. We therefore argue that the eMSTO phenomenon is mainly caused by extended star formation within the clusters; and (3) we find that v {sub esc} ≥ 15 km s{sup –1} out to ages of at least 100 Myr for all clusters featuring eMSTOs, and v {sub esc} ≤ 12 km s{sup –1} at all ages for two lower-mass clusters in the same age range that do not show eMSTOs. We argue that eMSTOs only occur for clusters whose early escape velocities are higher than the wind velocities of stars that provide material from which second-generation stars can form. The threshold of 12-15 km s{sup –1} is consistent with wind velocities of intermediate-mass asymptotic giant branch stars and massive binary stars in the literature.« less
UIT Observations of Early-Type Galaxies and Analysis of the FUSE Spectrum of a Subdwarf B Star
Ohl, Raymond G.; Krebs, Carolyn (Technical Monitor)
This work covers Ultraviolet Imaging Telescope (UIT) observations of early-type galaxies (155 nm) and Far Ultraviolet Spectroscopic Explorer (FUSE) spectra of a Galactic subdwarf B star (sdB). Early UV space astronomy missions revealed that early-type galaxies harbor a population of stars with effective temperatures greater than that of the main sequence turn-off (about 6,000 K) and UV emission that is very sensitive to characteristics of the stellar population. We present UV (155 nm) surface photometry and UV-B color profiles for 8 E and SO galaxies observed by UIT. Some objects have de Vaucouleurs surface brightness profiles, while others have disk-like profiles, but we find no other evidence for the presence of a disk or young, massive stars. There is a wide range of UV-B color gradients, but there is no correlation with metallicity gradients. SdB stars are the leading candidate UV emitters in old, high metallicity stellar populations (e.g., early-type galaxies). We observed the Galactic sdB star PG0749+658 with FUSE and derived abundances with the aim of constraining models of the heavy element distribution in sdB atmospheres. All of the elements measured are depleted with respect to solar, except for Cr and Mn, which are about solar, and Ni, which is enhanced. This work was supported in part by NASA grants NAG5-700 and NAG5-6403 to the University of Virginia and NAS5-32985 to Johns Hopkins University.
Two-dimensional models of early-type fast rotating stars: the ESTER project
In this talk I present the latest results of the ESTER project that has taken up the challenge of building two dimensional (axisymmetric) models of stars rotating at any rotation rate. In particular, I focus on main sequence massive and intermediate mass stars. I show what should be expected in such stars as far as the differential rotation and the associated meridional circulation are concerned, notably the emergence of a Stewartson layer along the tangent cylinder of the core. I also indicate what may be inferred about the evolution of an intermediate-mass star at constant angular momentum and how Be stars may form. I finally give some comparisons between models and observations of the gravity darkening on some nearby fast rotators as it has been derived from interferometric observations. In passing, I also discuss how 2D models can help to recover the fundamental parameters of a star.
9 Sagittarii: uncovering an O-type spectroscopic binary with an 8.6 year period
Rauw, G.; Sana, H.; Spano, M.; Gosset, E.; Mahy, L.; De Becker, M.; Eenens, P.
Context. The O-type object 9 Sgr is a well-known synchrotron radio emitter. This feature is usually attributed to colliding-wind binary systems, but 9 Sgr was long considered a single star. Aims: We have conducted a long-term spectroscopic monitoring of this star to investigate its multiplicity and search for evidence for wind-wind interactions. Methods: Radial velocities are determined and analysed using various period search methods. Spectral disentangling is applied to separate the spectra of the components of the binary system. Results: We derive the first ever orbital solution of 9 Sgr. The system is found to consist of an O3.5 V((f+)) primary and an O5-5.5 V((f)) secondary moving around each other on a highly eccentric (e = 0.7), 8.6 year orbit. The spectra reveal no variable emission lines that could be formed in the wind interaction zone in agreement with the expected properties of the interaction in such a wide system. Conclusions: Our results provide further support to the paradigm of synchrotron radio emission from early-type stars being a manifestation of interacting winds in a binary system. Based on observations collected at the European Southern Observatory (La Silla, Chile and Cerro Paranal, Chile) and the San Pedro Mártir observatory (Mexico).Appendix A is available in electronic form at http://www.aanda.orgThe reduced spectra are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/542/A95
Spiral-like star-forming patterns in CALIFA early-type galaxies
Gomes, J. M.; Papaderos, P.; Vílchez, J. M.; Kehrig, C.; Iglesias-Páramo, J.; Breda, I.; Lehnert, M. D.; Sánchez, S. F.; Ziegler, B.; Dos Reis, S. N.; Bland-Hawthorn, J.; Galbany, L.; Bomans, D. J.; Rosales-Ortega, F. F.; Walcher, C. J.; García-Benito, R.; Márquez, I.; Del Olmo, A.; Mollá, M.; Marino, R. A.; Catalán-Torrecilla, C.; González Delgado, R. M.; López-Sánchez, �. R.; Califa Collaboration
Based on a combined analysis of SDSS imaging and CALIFA integral field spectroscopy data, we report on the detection of faint (24 < 26) star-forming spiral-arm-like features in the periphery of three nearby early-type galaxies (ETGs). These features are of considerable interest because they document the still ongoing inside-out growth of some local ETGs and may add valuable observational insight into the origin and evolution of spiral structure in triaxial stellar systems. A characteristic property of the nebular component in the studied ETGs, classified I+, is a two-radial-zone structure, with the inner zone that displays faint (EW(Hα) ≃ 1 Å) low-ionization nuclear emission-line region (LINER) properties, and the outer one (3 Å
Probing Minor-merger-driven Star Formation In Early-type Galaxies Using Spatially-resolved Spectro-photometric Studies
Kaviraj, Sugata; Crockett, M.; Silk, J.; O'Connell, R. W.; Whitmore, B.; Windhorst, R.; Cappellari, M.; Bureau, M.; Davies, R.
Recent studies that leverage the rest-frame ultraviolet (UV) spectrum have revealed widespread recent star formation in early-type galaxies (ETGs), traditionally considered to be old, passively-evolving systems. This recent star formation builds 20% of the ETG stellar mass after z 1, driven by repeated minor mergers between ETGs and small, gas-rich satellites. We demonstrate how spatially-resolved studies, using a combination of high-resolution UV-optical imaging and integral-field spectroscopy (IFS), is a powerful tool to quantify the assembly history of individual ETGs and elucidate the poorly-understood minor-merger process. Using a combination of WFC3 UV-optical (2500-8200 angstroms) imaging and IFS from the SAURON project of the ETG NGC 4150, we show that this galaxy experienced a merger with mass ratio 1:15 around 0.9 Gyr ago, which formed 3% of its stellar mass and a young kinematically-decoupled core. A UV-optical analysis of its globular cluster system shows that the bulk of the stars locked up in these clusters likely formed 6-7 Gyrs in the past. We introduce a new HST-WFC3 programme, approved in Cycle 19, which will leverage similar UV-optical imaging of a representative sample of nearby ETGs from SAURON to study the recent star formation and its drivers in unprecedented detail and put definitive constraints on minor-merger-driven star formation in massive galaxies at late epochs.
The Abundances of the Fe Group Elements in Early B Stars in the Magellanic Clouds and Our Galaxy
Peters, Geraldine Joan; Adelman, Saul Joseph
The abundances of the Fe-peak elements (Ti, V, Cr, Mn, Fe, Co, and Ni) are of interest as they are important for assessing opacities for stellar evolution calculations, confirming theoretical calculations of explosive nucleosynthesis, and inferring the past history of supernova activity in a galaxy. FUSE FUV spectra of early B stars in the LMC and SMC and HST/STIS FUV/NUV spectra of nearby B stars in our galaxy are analyzed with the Hubeny/Lanz programs TLUSTY/SYNSPEC to determine abundance for the Fe group elements and produce a map of these abundances in the Magellanic Clouds (MC) and Magellanic Bridge (MB). Except for four weak multiplets of Fe III there are no measurable lines from the Fe group in the optical region. The Fe group species found in the FUV spectra of early B stars are primarily in the second stage of ionization. The best set of lines in the FUSE spectral region are Fe III (UV1), V III 1150 Å, and Cr III 1137 Å. Analysis of the galactic B stars provides a good assessment of the reliability of the atomic parameters that are used for the MC calculations. Twenty-two early B stars in the MC and MB and five in our galaxy were analyzed. In general the Fe group abundances range from solar to slightly below solar in our region of the galaxy. But in the MCs the abundances of V, Cr, and Fe tend to be significantly lower than the mean metal abundances for the galaxy. Maps of the Fe group abundances and their variations in the LMC and SMC, tracers of recent enrichment of the ISM from supernova activity, are shown. Support from NASA grants NAG5-13212, NNX10AD66G, STScI HST-GO-13346.22, and USC's Women in Science and Engineering (WiSE) program is greatly appreciated.
X-ray diagnostics of massive star winds
Oskinova, L. M.; Ignace, R.; Huenemoerder, D. P.
Observations with powerful X-ray telescopes, such as XMM-Newton and Chandra, significantly advance our understanding of massive stars. Nearly all early-type stars are X-ray sources. Studies of their X-ray emission provide important diagnostics of stellar winds. High-resolution X-ray spectra of O-type stars are well explained when stellar wind clumping is taking into account, providing further support to a modern picture of stellar winds as non-stationary, inhomogeneous outflows. X-ray variability is detected from such winds, on time scales likely associated with stellar rotation. High-resolution X-ray spectroscopy indicates that the winds of late O-type stars are predominantly in a hot phase. Consequently, X-rays provide the best observational window to study these winds. X-ray spectroscopy of evolved, Wolf-Rayet type, stars allows to probe their powerful metal enhanced winds, while the mechanisms responsible for the X-ray emission of these stars are not yet understood.
uvbyβ photometry of early type open cluster and field stars
Handler, G.
Context. The β Cephei stars and slowly pulsating B (SPB) stars are massive main sequence variables. The strength of their pulsational driving strongly depends on the opacity of iron-group elements. As many of those stars naturally occur in young open clusters, whose metallicities can be determined in several fundamental ways, it is logical to study the incidence of pulsation in several young open clusters. Aims: To provide the foundation for such an investigation, Strömgren-Crawford uvbyβ photometry of open cluster target stars was carried out to determine effective temperatures, luminosities, and therefore cluster memberships. Methods: In the course of three observing runs, uvbyβ photometry for 168 target stars was acquired and transformed into the standard system by measurements of 117 standard stars. The list of target stars also included some known cluster and field β Cephei stars, as well as β Cephei and SPB candidates that are targets of the asteroseismic part of the Kepler satellite mission. Results: The uvbyβ photometric results are presented. The data are shown to be on the standard system, and the properties of the target stars are discussed: 140 of these are indeed OB stars, a total of 101 targets lie within the β Cephei and/or SPB star instability strips, and each investigated cluster contains such potential pulsators. Conclusions: These measurements will be taken advantage of in a number of subsequent publications. Based on measurements obtained at McDonald Observatory of the University of Texas at Austin.Tables 3-6 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/528/A148
GHRS observations and theoretical modeling of early type stars in R136a
de Koter, A.; Heap, S.; Hubeny, I.; Lanz, T.; Hutchings, J.; Lamers, H. J. G. L. M.; Maran, S.; Schmutz, W.
We present the first spectroscopic observations of individual stars in R136a, the most dense part of the starburst cluster 30 Doradus in the LMC. Spectra of two stars are scheduled to be obtained with the GHRS on board the HST: R136a5, the brightest of the complex and R136a2, a Wolf-Rayet star of type WN. The 30 Doradus cluster is the only starburst region in which individual stars can be studied. Therefore, quantitative knowledge of the basic stellar parameters will yield valuable insight into the formation of massive stars in starbursts and into their subsequent evolution. Detailed modeling of the structure of the atmosphere and wind of these stars will also lead to a better understanding of the mechanism(s) that govern their dynamics. We present the first results of our detailed quantitative spectral analysis using state-of-the-art non-LTE model atmospheres for stars with extended and expanding atmospheres. The models are computed using the Improved-Sobolev Approximation wind code (ISA-WIND) of de Koter, Schmutz & Lamers (1993, A&A 277, 561), which has been extended to include C, N and Si. Our model computations are not based on the core-halo approximation, but use a unified treatment of the photosphere and wind. This approach is essential for Wolf-Rayet stars. Our synthetic spectra, dominated by the P Cygni profiles of the UV resonance lines, also account for the numerous weak metal lines of photospheric origin.
Observational knowledge about the physical properties of O stars
Underhill, A. B.
Information about the effective temperatures, radii, and masses of O-type stars is presented. It is argued that rapid variations in the amount of light from O stars and the spectral distribution are a result chiefly of changes which occur in the envelope of the star. The stability of the photospheric layers of O stars against convection is reviewed and it is noted that late O stars and early B stars have a convection zone in the deeper parts of the photosphere. This convection zone is due to the second ionization of helium. Evidence is reviewed that most of the line-profile changes seen for O stars are generated by changes in the physical state of the mantle of the star, that is of the outer atmosphere where the deposition of non-radiative energy and momentum controls the physical state of the atmosphere. The physical state of the mantle may change in response to changes in the upper envelope of a star with a different time constant than the photosphere does.
BRITE-Constellation high-precision time-dependent photometry of the early O-type supergiant ζ Puppis unveils the photospheric drivers of its small- and large-scale wind structures
Ramiaramanantsoa, Tahina; Moffat, Anthony F. J.; Harmon, Robert; Ignace, Richard; St-Louis, Nicole; Vanbeveren, Dany; Shenar, Tomer; Pablo, Herbert; Richardson, Noel D.; Howarth, Ian D.; Stevens, Ian R.; Piaulet, Caroline; St-Jean, Lucas; Eversberg, Thomas; Pigulski, Andrzej; Popowicz, Adam; Kuschnig, Rainer; Zocłońska, Elżbieta; Buysschaert, Bram; Handler, Gerald; Weiss, Werner W.; Wade, Gregg A.; Rucinski, Slavek M.; Zwintz, Konstanze; Luckas, Paul; Heathcote, Bernard; Cacella, Paulo; Powles, Jonathan; Locke, Malcolm; Bohlsen, Terry; Chené, André-Nicolas; Miszalski, Brent; Waldron, Wayne L.; Kotze, Marissa M.; Kotze, Enrico J.; Böhm, Torsten
From 5.5 months of dual-band optical photometric monitoring at the 1 mmag level, BRITE-Constellation has revealed two simultaneous types of variability in the O4I(n)fp star ζ Puppis: one single periodic non-sinusoidal component superimposed on a stochastic component. The monoperiodic component is the 1.78-d signal previously detected by Coriolis/Solar Mass Ejection Imager, but this time along with a prominent first harmonic. The shape of this signal changes over time, a behaviour that is incompatible with stellar oscillations but consistent with rotational modulation arising from evolving bright surface inhomogeneities. By means of a constrained non-linear light-curve inversion algorithm, we mapped the locations of the bright surface spots and traced their evolution. Our simultaneous ground-based multisite spectroscopic monitoring of the star unveiled cyclical modulation of its He II λ4686 wind emission line with the 1.78-d rotation period, showing signatures of corotating interaction regions that turn out to be driven by the bright photospheric spots observed by BRITE. Traces of wind clumps are also observed in the He II λ4686 line and are correlated with the amplitudes of the stochastic component of the light variations probed by BRITE at the photosphere, suggesting that the BRITE observations additionally unveiled the photospheric drivers of wind clumps in ζ Pup and that the clumping phenomenon starts at the very base of the wind. The origins of both the bright surface inhomogeneities and the stochastic light variations remain unknown, but a subsurface convective zone might play an important role in the generation of these two types of photospheric variability.
Five Spectroscopic Categories of O-Type Candidate GRB Progenitors
Walborn, Nolan R.; Rojas-Montes, Eliceth; Evans, Chris J.; Maíz Apellániz, Jesús; Wade, Gregg A.
Five categories of peculiar O-type stars in the Galaxy and Magellanic Clouds that each combine three or four of the canonical GRB properties of magnetic fields, high mass, rarity, rapid rotation, and runaway space motions are displayed. (1) The Of?p stars were initially isolated as a peculiar spectroscopic category which was later found to undergo spectacular periodic variations; they are now understood as the most massive oblique magnetic rotators. All five Galactic members plus two related objects now have magnetic field detections, including one of 20 kG, with rotational periods ranging from a week to >50 yrs. There are also three spectroscopic members in the MCs, for which magnetic observations remain to be undertaken. (2) The ONn stars are rapidly rotating, nitrogen-rich, late-O giants at least several of which are runaways. (3) The Onfp stars are another category first described in terms of certain spectral peculiarities; they are now known to be massive, evolved rapid rotators with strong winds, which theoretically should not exist in the single-star regime. Many are in binary systems, perhaps spun up by mass transfer, while others may be mergers, and at least some are runaways. This category calls into question the assumption that GRBs can occur only at low metallicity where weaker winds allow high rotation to be preserved in evolved objects. (4) A population of young extreme rotators, including the two most rapid known at v sin i of 600 km/sec, lies at the peripheries of the 30 Doradus ionizing clusters. Peculiar radial velocities as well as their locations support an ejection hypothesis, currently under further investigation by means of proper motions. (5) At least two extremely massive O2 stars have also been ejected from 30 Doradus, most likely by dynamical processes since there have not yet been any SN in the dense central cluster R136. Presumably all of these stars must reach LBV and/or WR stages before collapsing, so they are not immediate GRB
Empirical effective temperatures and bolometric corrections for early-type stars
Code, A. D.; Bless, R. C.; Davis, J.; Brown, R. H.
An empirical effective temperature for a star can be found by measuring its apparent angular diameter and absolute flux distribution. The angular diameters of 32 bright stars in the spectral range O5f to F8 have recently been measured with the stellar interferometer at Narrabri Observatory, and their absolute flux distributions have been found by combining observations of ultraviolet flux from the Orbiting Astronomical Observatory (OAO-2) with ground-based photometry. In this paper, these data have been combined to derive empirical effective temperatures and bolometric corrections for these 32 stars.
Neutron-captures in Low Mass Stars and the Early Solar System Record of Short-lived Radioactivities
Busso, Maurizio; Vescovi, Diego; Trippella, Oscar; Palmerini, Sara; Cristallo, Sergio; Piersanti, Luciano
Noticeable improvements were recently introduced in the modelling of n-capture nucleosynthesis in the advanced evolutionary stages of giant stars (Asymptotic Giant Branch, or AGB, stars). Two such improvements are closely linked together and concern the introduction of non-parameterized, physical models for extended mixing processes and the adoption of accurate reaction rates for H- and He-burning reactions, including the one for the main neutron source 13C(α,n)16O. These improvements profited of a longstanding collaboration between stellar physicists and C. Spitaleri's team and of his seminal work both as a leader in the Nuclear Astrophysics scenario and as a talent-scout in the recruitment of young researchers in the field. We present an example of the innovative results that can be obtained thanks to the novelties introduced, by estimating the contributions from a nearby AGB star to the synthesis of short-lived (t1/2 ≤ 10 Myr) radioactive nuclei which were alive in early Solar System condensates. We find that the scenario indicating an AGB star as the source of such radioactivities, discussed for many years by researchers in this field, appears now to be no longer viable, when the mentioned improvements of AGB models and nuclear parameters are considered.
The Abundances of the Fe Group Elements in Three Early B Stars in the Large Magellanic Cloud
Peters, G. J.; Adelman, S. J.
The photospheric abundances of V, Cr, and Fe have been determined for three sharp-lined early B stars in the Large Magellanic Cloud using FUV spectra obtained from the Far Ultraviolet Spectroscopic Explorer (FUSE) and the Kurucz LTE model atmosphere/spectrum synthesis codes ATLAS9/SYNTHE. The program stars include NGC1818/D1, NGC2004/B15, and NGC2004/B30 (star designations are from Robertson 1974, A&AS, 15, 261). The calculations were carried through with model parameters close to those adopted by Korn et al. (2000, A&A, 353, 655). Values of Teff, log g, ξ T, and v sin I are 25000/4.0/0/30, 20000/3.1/6/25, and 23500/3.3/14/30 for NGC1818/D1, NGC2004/B15, and NGC2004/B30, respectively. The abundances quoted below are in sequence for the latter stars. The vanadium abundances, [V/H], determined from V III λ λ 1150,1152 (UV 2), are -0.6, -0.9, and -0.9 dex. Cr was determined from Cr III λ λ 1118,1136. Values of -0.5, -0.8, and -0.7 dex were found. Uncertainties in the V and Cr abundances are ˜0.3 dex. The Fe abundance is primarily from 7 lines of Fe III (UV 1) in the region λ λ 1122-32. Values are -0.8±0.3, ˜-1.1, and -0.4±0.3. Since there is no evidence for N enhancement in the program stars ([N/H] ˜ -0.9, -1.0, and -0.6 from the N III doublet at 1183,1184 Å) the photospheric abundances have probably not been altered by mixing of processed material from the star's interior and the derived abundances represent pristine values for the two young clusters in the LMC. It should be noted that the N and Fe abundances derived for NGC1818/D1 are about 0.5 dex lower than those determined by Korn et al. from much weaker optical lines. We will discuss possible reasons for the discrepancy. The generally low abundances for the Fe group elements in these young cluster B stars imply that supernova activity has been minimal in the regions of the LMC in which the stars were formed. GJP appreciates support from NASA grant NAG5-13212.
The IUE Mega Campaign: Wind Variability and Rotation in Early-Type Stars
Massa, D.; Fullerton, A. W.; Nichols, J. S.; Owocki, S. P.; Prinja, R. K.; St-Louis, N.; Willis, A. J.; Altner, B.; Bolton, C. T.; Cassinelli, J. P.;
Wind variability in OB stars may be ubiquitous and a connection between projected stellar rotation velocity and wind activity is well established. However, the origin of this connection is unknown. To probe the nature of the rotation connection, several of the attendees at the workshop on Instability and Variability of Hot-Star Winds drafted an IUE observing proposal. The goal of this program was to follow three stars for several rotations to determine whether the rotation connection is correlative or causal. The stars selected for monitoring all have rotation periods less than or equal to 5 days. They were HD 50896 (WN5), HD 64760 (BO.5 Ib), and HD 66811 (zeta Pup; 04 If(n)). During 16 days of nearly continuous observations in 1995 January (dubbed the 'MEGA' campaign), 444 high-dispersion IUE spectra of these stars were obtained. This Letter presents an overview of the results of the MEGA campaign and provides an introduction to the three following Letters, which discuss the results for each star.
The boron-to-beryllium ratio in halo stars - A signature of cosmic-ray nucleosynthesis in the early Galaxy
Walker, T. P.; Steigman, G.; Schramm, D. N.; Olive, K. A.; Fields, B.
We discuss Galactic cosmic-ray (GCR) spallation production of Li, Be, and B in the early Galaxy with particular attention to the uncertainties in the predictions of this model. The observed correlation between the Be abundance and the metallicity in metal-poor Population II stars requires that Be was synthesized in the early Galaxy. We show that the observations and such Population II GCR synthesis of Be are quantitatively consistent with the big bang nucleosynthesis production of Li-7. We find that there is a nearly model independent lower bound to B/Be of about 7 for GCR synthesis. Recent measurements of B/Be about 10 in HD 140283 are in excellent agreement with the predictions of Population II GCR nucleosynthesis. Measurements of the boron abundance in additional metal-poor halo stars is a key diagnostic of the GCR spallation mechanism. We also show that Population II GCR synthesis can produce amounts of Li-6 which may be observed in the hottest halo stars.
Is the Ratio of Observed X-ray Luminosity to Bolometric Luminosity in Early-type Stars Really a Constant?
Waldron, W. L.
The observed X-ray emission from early-type stars can be explained by the recombination stellar wind model (or base coronal model). The model predicts that the true X-ray luminosity from the base coronal zone can be 10 to 1000 times greater than the observed X-ray luminosity. From the models, scaling laws were found for the true and observed X-ray luminosities. These scaling laws predict that the ratio of the observed X-ray luminosity to the bolometric luminosity is functionally dependent on several stellar parameters. When applied to several other O and B stars, it is found that the values of the predicted ratio agree very well with the observed values.
The abundances of the elements in sharp-lined early type stars
Adelman, Saul J.
An International Ultraviolet Explorer (IUE) observing strategy that has yielded co-added spectra with enhanced S/N ratios for several A and B stars was established. New observations by Roby and Adelman using the same technique were added two new Hg-Mn stars into this sample. A long-term study of elemental abundances in this uniform, high-quality set of IUE spectra for 13 stars was begun. The first stages of this project are reported: abundances for N, Cr, Mn, Fe, Co, and Ni. The study of the Fe-peak elements show that our data set can provide accurate abundances and that abundances obtained from UV and optical spectra often are in good agreement. The groundwork for selfconsistent abundance analyses of more exotic elements in our long term project was provided.
Probing the chemical environments of early star formation: A multidisciplinary approach
Hardegree-Ullman, Emily Elizabeth
Chemical compositions of prestellar and protostellar environments in the dense interstellar medium are best quantified using a multidisciplinary approach. For my dissertation, I completed two projects to measure molecular abundances during the earliest phases of star formation. The first project investigates gas phase CO depletion in molecular cloud cores, the progenitors of star systems, using infrared photometry and molecular line spectroscopy at radio wavelengths. Hydrogenation of CO depleted onto dust is an important first step toward building complex organic molecules. The second project constrains polycyclic aromatic hydrocarbon (PAH) abundances toward young stellar objects (YSO). Band strengths measured from laboratory spectroscopy of pyrene/water ice mixtures were applied to estimate abundances from features attributed to PAHs in observational YSO spectra. PAHs represent a distinct but important component of interstellar organic material that is widely observed but not well quantified in star-forming regions.
Multiplicity At Early Stages Of Star Formation, Small Clusters. Observations Overview
Saito, Masao
The SOLA (Soul of Lupus with ALMA) project is conducting comprehensive studies of the Lupus Molecular Clouds and their star formation processes covering 10-10^4 AU scale. Our goal is to exploit ALMA and other facilities over a wide wavelength range to establish a prototypical low-mass star forming scenario based on the Lupus region. In the presentation, we will focus on angular momentum in dense cores in a filament, molecular outflows from young stars, and Class 0/I binary survey in Lupus as well as overview of our projects. Our binary survey was conducted in ALMA cycle 2 and achieved at 0.2-0.3 arcsec resolution discovering new binary systems in Lupus. At the same time, we obtained EX Lup, EXor type burst source, data in ALMA Cycle 3.
Magnetic fields in non-convective regions of stars.
Braithwaite, Jonathan; Spruit, Henk C
We review the current state of knowledge of magnetic fields inside stars, concentrating on recent developments concerning magnetic fields in stably stratified (zones of) stars, leaving out convective dynamo theories and observations of convective envelopes. We include the observational properties of A, B and O-type main-sequence stars, which have radiative envelopes, and the fossil field model which is normally invoked to explain the strong fields sometimes seen in these stars. Observations seem to show that Ap-type stable fields are excluded in stars with convective envelopes. Most stars contain both radiative and convective zones, and there are potentially important effects arising from the interaction of magnetic fields at the boundaries between them; the solar cycle being one of the better known examples. Related to this, we discuss whether the Sun could harbour a magnetic field in its core. Recent developments regarding the various convective and radiative layers near the surfaces of early-type stars and their observational effects are examined. We look at possible dynamo mechanisms that run on differential rotation rather than convection. Finally, we turn to neutron stars with a discussion of the possible origins for their magnetic fields.
Magnetic fields in non-convective regions of stars
Braithwaite, Jonathan
We review the current state of knowledge of magnetic fields inside stars, concentrating on recent developments concerning magnetic fields in stably stratified (zones of) stars, leaving out convective dynamo theories and observations of convective envelopes. We include the observational properties of A, B and O-type main-sequence stars, which have radiative envelopes, and the fossil field model which is normally invoked to explain the strong fields sometimes seen in these stars. Observations seem to show that Ap-type stable fields are excluded in stars with convective envelopes. Most stars contain both radiative and convective zones, and there are potentially important effects arising from the interaction of magnetic fields at the boundaries between them; the solar cycle being one of the better known examples. Related to this, we discuss whether the Sun could harbour a magnetic field in its core. Recent developments regarding the various convective and radiative layers near the surfaces of early-type stars and their observational effects are examined. We look at possible dynamo mechanisms that run on differential rotation rather than convection. Finally, we turn to neutron stars with a discussion of the possible origins for their magnetic fields. PMID:28386410
Ghostly Halos in Dwarf Galaxies: a probe of star formation in the Early Universe
Kang, Hoyoung; Ricotti, Massimo
We carry out numerical simulations to characterize the size, stellar mass, and stellar mass surface density of extended stellar halos in dwarf galaxies as a function of dark matter halo mass. We expect that for galaxies smaller than a critical value, these ghostly halos will not exist because the smaller galactic subunits that build it up, do not form any stars. The detection of ghostly halos around isolated dwarf galaxies is a sensitive test of the efficiency of star formation in the first galaxies and of whether ultra-faint dwarf satellites of the Milky Way are fossils of the first galaxies.
Solution of the comoving-frame equation of transfer in spherically symmetric flows. V - Multilevel atoms. [in early star atmospheres
Mihalas, D.; Kunasz, P. B.
The coupled radiative transfer and statistical equilibrium equations for multilevel ionic structures in the atmospheres of early-type stars are solved. Both lines and continua are treated consistently; the treatment is applicable throughout a transonic wind, and allows for the presence of background continuum sources and sinks in the transfer. An equivalent-two-level-atoms approach provides the solution for the equations. Calculations for simplified He (+)-like model atoms in parameterized isothermal wind models indicate that subordinate line profiles are sensitive to the assumed mass-loss rate, and to the assumed structure of the velocity law in the atmospheres.
Far-ultraviolet spectrophotometry of two very hot O type subdwarfs
Drilling, J. S.; Holberg, J. B.; Schoenberner, D.
As a result of a spectroscopic survey of stars classified as nonemission OB+, Drilling (1983) has detected 12 new subluminous O stars. It was found that these stars are the hottest known O type subdwarfs. The effective temperatures of the stars are 60,000 K or higher. It has been possible to observe two of these stars with Voyager 1, taking into account LSE 21 and LS IV +10.9 deg. LSE 21 is one of the hottest of the new subdwarfs, with an effective temperature of at least 100,000 K. The optical spectrum indicates a hydrogen-rich atmosphere of high surface gravity. LX IV +10.9 deg is one of the cooler objects with an effective temperature of 65,000 K. The optical spectrum indicates an extremely helium-rich atmosphere and a somewhat lower surface gravity than LSE 21. The Voyager 1 observations confirm the temperature scale set up by Schoenberger and Drilling (1984) for the hottest O type subdwarfs.
An ALMA view of star formation efficiency suppression in early-type galaxies after gas-rich minor mergers
van de Voort, Freeke; Davis, Timothy A.; Matsushita, Satoki; Rowlands, Kate; Shabala, Stanislav S.; Allison, James R.; Ting, Yuan-Sen; Sansom, Anne E.; van der Werf, Paul P.
Gas-rich minor mergers contribute significantly to the gas reservoir of early-type galaxies (ETGs) at low redshift, yet the star formation efficiency (SFE; the star formation rate divided by the molecular gas mass) appears to be strongly suppressed following some of these events, in contrast to the more well-known merger-driven starbursts. We present observations with the Atacama Large Millimeter/submillimeter Array (ALMA) of six ETGs, which have each recently undergone a gas-rich minor merger, as evidenced by their disturbed stellar morphologies. These galaxies were selected because they exhibit extremely low SFEs. We use the resolving power of ALMA to study the morphology and kinematics of the molecular gas. The majority of our galaxies exhibit spatial and kinematical irregularities, such as detached gas clouds, warps, and other asymmetries. These asymmetries support the interpretation that the suppression of the SFE is caused by dynamical effects stabilizing the gas against gravitational collapse. Through kinematic modelling we derive high velocity dispersions and Toomre Q stability parameters for the gas, but caution that such measurements in edge-on galaxies suffer from degeneracies. We estimate merger ages to be about 100 Myr based on the observed disturbances in the gas distribution. Furthermore, we determine that these galaxies lie, on average, two orders of magnitude below the Kennicutt-Schmidt relation for star-forming galaxies as well as below the relation for relaxed ETGs. We discuss potential dynamical processes responsible for this strong suppression of star formation surface density at fixed molecular gas surface density.
Nearby Early-type Galactic Nuclei at High Resolution: Dynamical Black Hole and Nuclear Star Cluster Mass Measurements
Nguyen, Dieu D.; Seth, Anil C.; Neumayer, Nadine; Kamann, Sebastian; Voggel, Karina T.; Cappellari, Michele; Picotti, Arianna; Nguyen, Phuong M.; Böker, Torsten; Debattista, Victor; Caldwell, Nelson; McDermid, Richard; Bastian, Nathan; Ahn, Christopher C.; Pechetti, Renuka
We present a detailed study of the nuclear star clusters (NSCs) and massive black holes (BHs) of four of the nearest low-mass early-type galaxies: M32, NGC 205, NGC 5102, and NGC 5206. We measure the dynamical masses of both the BHs and NSCs in these galaxies using Gemini/NIFS or VLT/SINFONI stellar kinematics, Hubble Space Telescope (HST) imaging, and Jeans anisotropic models. We detect massive BHs in M32, NGC 5102, and NGC 5206, while in NGC 205, we find only an upper limit. These BH mass estimates are consistent with previous measurements in M32 and NGC 205, while those in NGC 5102 and NGC 5206 are estimated for the first time and both found to be <106 M ⊙. This adds to just a handful of galaxies with dynamically measured sub-million M ⊙ central BHs. Combining these BH detections with our recent work on NGC 404's BH, we find that 80% (4/5) of nearby, low-mass ({10}9{--}{10}10 M ⊙ {σ }\\star ∼ 20{--}70 km s‑1) early-type galaxies host BHs. Such a high occupation fraction suggests that the BH seeds formed in the early epoch of cosmic assembly likely resulted in abundant seeds, favoring a low-mass seed mechanism of the remnants, most likely from the first generation of massive stars. We find dynamical masses of the NSCs ranging from 2 to 73 × 106 M ⊙ and compare these masses to scaling relations for NSCs based primarily on photometric mass estimates. Color gradients suggest that younger stellar populations lie at the centers of the NSCs in three of the four galaxies (NGC 205, NGC 5102, and NGC 5206), while the morphology of two are complex and best fit with multiple morphological components (NGC 5102 and NGC 5206). The NSC kinematics show they are rotating, especially in M32 and NGC 5102 (V/{σ }\\star ∼ 0.7).
Weak and Compact Radio Emission in Early High-Mass Star Forming Regions
Rosero, Viviana; P. Hofner, M. Claussen, S. Kurtz, R. Cesaroni, E. D. Araya, C. Carrasco-González, L. F. Rodríguez, K. M. Menten, F. Wyrowski, L. Loinard, S. P. Ellingsen
High-mass protostars are difficult to detect: they have short evolutionary timescales, they tend to be located at large distances, and they are usually embedded within complicated cluster environments. In this work, we aimed to identify and analyze candidates at the earliest stages of high-mass star formation, where only low-level (< 1 mJy) radio emission is expected. We used the Karl G. Jansky Very Large Array to achieve one of the most sensitive (image RMS < 3 -- 10 μJy/beam) centimeter continuum surveys towards high-mass star forming regions to date, with observations at 1.3 and 6 cm and an angular resolution < 0.5". The sample is composed of cold molecular clumps with and without infrared sources (CMC--IRs and CMCs, respectively) and hot molecular cores (HMCs), covering a wide range of parameters such as bolometric luminosity and distance. We detected 70 radio continuum sources that are associated with dust clumps, most of which are weak and compact. We detected centimeter wavelength sources in 100% of our HMCs, which is a higher fraction than previously expected and suggests that radio continuum may be detectable at weak levels in all HMCs. The lack of radio detections for some objects in the sample (including most CMCs) contributes strong evidence that these are prestellar clumps, providing interesting constraints and ideal follow up candidates for studies of the earliest stages of high-mass stars. Our results show further evidence for an evolutionary sequence in the formation of high-mass stars, from starless cores (i.e., CMCs) to relatively more evolved ones (i.e., HMCs). Many of our detections have morphologies and other observational parameters that resemble collimated ionized jets, which is highly relevant for recent theoretical models based on core accretion that predict that the first stages of ionization from high-mass stars are in the form of jets. Additionally, we found that properties of ionized jets from low and high-mass stars are extremely well
The early dynamical evolution of star clusters near the Galactic Centre
Park, So-Myoung; Goodwin, Simon P.; Kim, Sungsoo S.
We examine the dynamical evolution of both Plummer sphere and substructured (fractal) star-forming regions in Galactic Centre (GC) strong tidal fields to see what initial conditions could give rise to an Arches-like massive star cluster by ˜2 Myr. We find that any initial distribution has to be contained within its initial tidal radius to survive, which sets a lower limit of the initial density of the Arches of ˜600 M⊙ pc-3 if the Arches is at 30 pc from the GC, or ˜200 M⊙ pc-3 if the Arches is at 100 pc from the GC. Plummer spheres that survive change little other than to dynamically mass segregate, but initially fractal distributions rapidly erase substructure, dynamically mass segregate and by 2 Myr look extremely similar to initial Plummer spheres, therefore it is almost impossible to determine the initial conditions of clusters in strong tidal fields.
We examine the dynamical evolution of both Plummer sphere and substructured (fractal) star forming regions in Galactic Centre (GC) strong tidal fields to see what initial conditions could give rise to an Arches-like massive star cluster by ˜2 Myr. We find that any initial distribution has to be contained within its initial tidal radius to survive, which sets a lower limit of the initial density of the Arches of ˜ 600 M⊙ pc-3 if the Arches is at 30 pc from the GC, or ˜ 200 M⊙ pc-3 if the Arches is at 100 pc from the GC. Plummer spheres that survive change little other than to dynamically mass segregate, but initially fractal distributions rapidly erase substructure, dynamically mass segregate and by 2 Myr look extremely similar to initial Plummer spheres, therefore it is almost impossible to determine the initial conditions of clusters in strong tidal fields.
Early-20th-century visual observations of M13 variable stars
Osborn, W.; Barnard, E. E.
In 1900 E. E. Barnard published 37 visual observations of Variable 2 (V2) in the globular clustter M13 made in 1899 and 1900. A review of Barnard's notebooks revealed he made many additional brightness estimates up to 1911, and he had also recorded the variations of V1 starting in 1904. These data provide the earliest-epoch light curves for these stars and thus are useful for studying their period changes. This paper presents Barnard's observations of the M13 variables along with their derived heliocentric Julian Dates and approximate V magnitudes. These include 231 unpublished observations of V2 and 94 of V1. How these data will be of value for determing period changes by these stars is described.
Different regions of line formation in the envelope of the early emission line star HD 190073
Ringuelet, A. E.; Rovira, M.; Cidale, L.; Sahade, J.
A description is presented of the spectral features that characterize the spectrum of HD 190073 both in the photographic region (360-660 nm), and in the IUE UV (115-320 nm). A number of different types of profiles can be distinguished, and this seems to imply that many different 'broad' regions of line formation coexist in the extended envelope of the star, including regions with densities differing in several orders of magnitude.
A survey of mass-loss effects in early-type stars
Snow, T. P., Jr.
Intermediate-resolution data obtained with the Copernicus satellite are surveyed in order to define the region in the H-R diagram where mass loss occurs. The survey includes 40 stars, providing good coverage of supergiants from O4 to A2 and main-sequence stars from O4 to B7 as well as spotty coverage of late O giants and intermediate to late B stars. The spectral transitions examined are primarily resonance lines of ions of abundant elements plus some lines arising from excited states (e.g., C III at 1175.7 A and Si IV at 1122.5 A). Observed P Cygni profiles are discussed along with interesting features of some individual profiles. The data are shown to indicate that mass-loss effects occur over a wide portion of the H-R diagram, that mass ejection generally occurs when the holometric magnitude is greater than -6.0, and that the mass-ejection rate is usually high enough to produce P Cygni profile whenever the N V feature at 1240 A is present in a spectrum.
The VLT-FLAMES Tarantula Survey . XXIV. Stellar properties of the O-type giants and supergiants in 30 Doradus
Ramírez-Agudelo, O. H.; Sana, H.; de Koter, A.; Tramper, F.; Grin, N. J.; Schneider, F. R. N.; Langer, N.; Puls, J.; Markova, N.; Bestenlehner, J. M.; Castro, N.; Crowther, P. A.; Evans, C. J.; García, M.; Gräfener, G.; Herrero, A.; van Kempen, B.; Lennon, D. J.; Maíz Apellániz, J.; Najarro, F.; Sabín-Sanjulián, C.; Simón-Díaz, S.; Taylor, W. D.; Vink, J. S.
Context. The Tarantula region in the Large Magellanic Cloud (LMC) contains the richest population of spatially resolved massive O-type stars known so far. This unmatched sample offers an opportunity to test models describing their main-sequence evolution and mass-loss properties. Aims: Using ground-based optical spectroscopy obtained in the framework of the VLT-FLAMES Tarantula Survey (VFTS), we aim to determine stellar, photospheric and wind properties of 72 presumably single O-type giants, bright giants and supergiants and to confront them with predictions of stellar evolution and of line-driven mass-loss theories. Methods: We apply an automated method for quantitative spectroscopic analysis of O stars combining the non-LTE stellar atmosphere model fastwind with the genetic fitting algorithm pikaia to determine the following stellar properties: effective temperature, surface gravity, mass-loss rate, helium abundance, and projected rotational velocity. The latter has been constrained without taking into account the contribution from macro-turbulent motions to the line broadening. Results: We present empirical effective temperature versus spectral subtype calibrations at LMC-metallicity for giants and supergiants. The calibration for giants shows a +1kK offset compared to similar Galactic calibrations; a shift of the same magnitude has been reported for dwarfs. The supergiant calibrations, though only based on a handful of stars, do not seem to indicate such an offset. The presence of a strong upturn at spectral type O3 and earlier can also not be confirmed by our data. In the spectroscopic and classical Hertzsprung-Russell diagrams, our sample O stars are found to occupy the region predicted to be the core hydrogen-burning phase by state-of-the-art models. For stars initially more massive than approximately 60 M⊙, the giant phase already appears relatively early on in the evolution; the supergiant phase develops later. Bright giants, however, are not
Cooking up the First Stars
NASA Image and Video Library
Scientists are simulating how the very first stars in our universe were born. The stars we see today formed out of collapsing clouds of gas and dust. In the very early universe, however, the stars had fewer ingredients available.
A Star Close Encounter
The potential planet-forming disk (or "protoplanetary disk") of a sun-like star is being violently ripped away by the powerful winds of a nearby hot O-type star in this image from NASA's Spitzer Space Telescope. At up to 100 times the mass of sun-like stars, O stars are the most massive and energetic stars in the universe. The O star can be seen to the right of the image, as the large orange spot with the white center. To the left, the comet-like structure is actually a neighboring solar system that is being destroyed by the O star's powerful winds and intense ultraviolet light. In a process called "photoevaporation," immense output from the O star heats up the nearby protoplanetary disk so much that gas and dust boil off, and the disk can no longer hold together. Photon (or light) blasts from the O star then strip the potential planet-forming disk off its neighbor star by blowing away evaporated material. This effect is illustrated in the smaller system's comet-like structure. The system is located about 2,450 light-years away in the star-forming cloud IC 1396. The image was taken with Spitzer's multiband imaging photometer instrument at 24 microns. The picture is a pseudo-color stretch representing intensity. Yellow and white represent hot areas, whereas purple and blue represent relatively cooler, fainter regions.
Really Hot Stars
galaxy, another has been found in the nearby galaxy IC 1613, and five others are situated in the Magellanic Clouds. Astronomers have also detected the presence of HeII ions in a number of remote galaxies undergoing a phase of intense star formation ("starburst galaxies") and in the vicinity of ultraluminous X-ray sources in very distant galaxies. What is going on in those remote objects in the early Universe? Do we see the action of young and very hot stars or is something unknown going on? What can the existence of those hot nebulae in young galaxies tell about the evolution of our own Milky Way? Searching for the energy source We would like to know, but those distant nebulae are unfortunately too faint to be studied in any reasonable detail, even by means of the largest available telescopes. The only way forward is therefore to look closer at the nearest ones in the hope that they will provide clues about the processes leading to the observed high excitation and thus help to better understand their cousins in those distant galaxies. There appears to be three possible answers to the basic question about the nature of the energetic sources that heat these strange emission nebulae: * very fast particles: if there is in the area a fast-moving gas (more than 100 km/s), the shock created by the impact of this material is able to heat the ambient interstellar medium sufficiently to produce a HeII nebula. * ultraviolet emission from massive stars: according to the most recent model calculations, even the most massive O-type stars do not emit enough ultraviolet light to ionize a sufficient number of helium atoms in the surrounding nebula to produce a detectable HeII nebula. However, some of the hottest stars of the so-called Wolf-Rayet (W-R) type (that are the evolved descendants of O-stars) may produce enough high energy emission to completely ionize the helium atoms in their surroundings. * intense X-ray emission: close binary stars in which one component is a "compact
The early stages of massive star formation: tracing the physical and chemical conditions in hot cores
Calcutt, Hannah
Molecules are essential to the formation of stars, by allowing radiation to escape the cloud and cooling to occur. Over 180 molecules have been detected in interstellar environments, ranging from comets to interstellar clouds. Their spectra are useful probes of the conditions in which these molecules form. Comparison of rest frequencies to observed frequencies can provide information about the velocity of gas and indicate physical structures. The density, temperature, and excitation conditions of gas can be determined directly from the spectra of molecules. Furthermore, by taking a chemical inventory of a particular object, one can gain an understanding of the chemical processes occurring within a cloud. The class of molecules known as complex molecules (>6 atoms), are of particular interest when probing the conditions in massive starforming environments, as they are observed to trace a more compact region than smaller molecules. This thesis details the work of my PhD, to explore how complex molecules can be used to trace the physical and chemical conditions in hot cores (HCs), one of the earliest stages of massive star formation. This work combines both the observations and chemical modelling of several different massive star-forming regions. We identify molecular transitions observed in the spectra of these regions, and calculate column densities and rotation temperatures of these molecules (Chapters 2 and 3). In Chapter 4, we chemically model the HCs, and perform a comparison between observational column densities and chemical modelling column densities. In Chapter 5, we look at the abundance ratio of three isomers, acetic acid, glycolaldehyde, and methyl formate, to ascertain whether this ratio can be used as an indicator of HC evolution. Finally, we explore the chemistry of the HC IRAS 17233-3606, to identify emission features in the spectra, and determine column densities and rotation temperatures of the detected molecules.
Zooming in on star formation in the brightest galaxies of the early Universe discovered with the Planck and Herschel satellites
Canameras, Raoul
Strongly gravitationally lensed galaxies offer an outstanding opportunity to characterize the most intensely star-forming galaxies in the high-redshift universe. In the most extreme cases, one can probe the mechanisms that underlie the intense star formation on the scales of individual star-forming regions. This requires very fortuitous gravitational lensing configurations offering magnification factors >>10, which are particularly rare toward the high-redshift dusty star-forming galaxies. The Planck's Dusty GEMS (Gravitationally Enhanced subMillimeter Sources) sample contains eleven of the brightest high-redshift galaxies discovered with the Planck submillimeter all-sky survey, with flux densities between 300 and 1000 mJy at 350 microns, factors of a few brighter than the majority of lensed sources previously discovered with other surveys. Six of them are above the 90% completeness limit of the Planck Catalog of Compact Sources (PCCS), suggesting that they are among the brightest high-redshift sources on the sky selected by their active star formation. This thesis comes within the framework of the extensive multi-wavelength follow-up programme designed to determine the overall properties of the high-redshift sources and to probe the lensing configurations. Firstly, to characterize the intervening lensing structures and calculate lensing models, I use optical and near/mid-infrared imaging and spectroscopy. I deduce that our eleven GEMS are aligned with intervening matter overdensities at intermediate redshift, either massive isolated galaxies or galaxy groups and clusters. The foreground sources exhibit evolved stellar populations of a few giga years, characteristic of early-type galaxies. Moreover, the first detailed models of the light deflection toward the GEMS suggest magnification factors systematically >10, and >20 for some lines-of-sight. Secondly, we observe the GEMS in the far-infrared and sub-millimeter domains in order to characterize the background
HAZMAT. I. The evolution of far-UV and near-UV emission from early M stars
Shkolnik, Evgenya L.; Barman, Travis S., E-mail: shkolnik@lowell.edu, E-mail: barman@lpl.arizona.edu
The spectral energy distribution, variability, and evolution of the high-energy radiation from an M dwarf planet host is crucial in understanding the planet's atmospheric evolution and habitability and in interpreting the planet's spectrum. The star's extreme-UV (EUV), far-UV (FUV), and near-UV (NUV) emission can chemically modify, ionize, and erode the atmosphere over time. This makes determining the lifetime exposure of such planets to stellar UV radiation critical for both the evolution of a planet's atmosphere and our potential to characterize it. Using the early M star members of nearby young moving groups, which sample critical ages in planet formation andmore » evolution, we measure the evolution of the GALEX NUV and FUV flux as a function of age. The median UV flux remains at a 'saturated' level for a few hundred million years, analogous to that observed for X-ray emission. By the age of the Hyades Cluster (650 Myr), we measure a drop in UV flux by a factor of 2-3 followed by a steep drop from old (several Gyrs) field stars. This decline in activity beyond 300 Myr follows roughly t {sup –1}. Despite this clear evolution, there remains a wide range, of 1-2 orders of magnitude, in observed emission levels at every age. These UV data supply the much-needed constraints to M dwarf upper-atmosphere models, which will provide empirically motivated EUV predictions and more accurate age-dependent UV spectra as inputs to planetary photochemical models.« less
Empirical mass-loss rates for 25 O and early B stars, derived from Copernicus observations
Gathier, R.; Lamers, H. J. G. L. M.; Snow, T. P.
Ultraviolet line profiles are fitted with theoretical line profiles in the cases of 25 stars covering a spectral type range from O4 to B1, including all luminosity classes. Ion column densities are compared for the determination of wind ionization, and it is found that the O VI/N V ratio is dependent on the mean density of the wind and not on effective temperature value, while the Si IV/N V ratio is temperature-dependent. The column densities are used to derive a mass-loss rate parameter that is empirically correlated against the mass-loss rate by means of standard stars with well-determined rates from IR or radio data. The empirical mass-loss rates obtained are compared with those derived by others and found to vary by as much as a factor of 10, which is shown to be due to uncertainties or errors in the ionization fractions of models used for wind ionization balance prediction.
Overview of Conceptual Design of Early VentureStar(TM) Configurations
Lockwood, M. K.
One of NASA's goals is to enable commercial access to space at a cost of $1000/lb (an order of magnitude less than today's cost) by approximately 2010. Based on results from the 1994 Congressionally mandated, NASA led, Access-to-Space Study, an all rocket-powered single-stage-to-orbit reusable launch vehicle was, selected as the best option for meeting the goal. To address the technology development issues and the follow-on development of an operational vehicle, NASA initiated the X-33 program. The focus of this paper is on the contributions made by the NASA Langley Research Center (LaRC), from 1997-1998, to the conceptual design of the Lockheed Martin Skunk Work's (LMSW) operational reusable single-stage-to-orbit VentureStar(sup TM) vehicle. The LaRC effort has been in direct support of LMSW and NASA Marshall Space Flight Center (MSFC). The primary objectives have been to reduce vehicle dry weight and improve flyability of the VentureStar(sup TM) concepts. This paper will briefly describe the analysis methods used and will present several of the concepts analyzed and design trades completed.
R associations. VI - The reddening law in dust clouds and the nature of early-type emission stars in nebulosity from a study of five associations
Herbst, W.; Warner, J. W.; Miller, D. P.; Herzog, A.
Positions, identification charts, UBVRIKLMN photometry and spectral types are given for stars, illuminating reflection nebulae that are visible on the POSS prints, which have been identified in five associations. With a ratio of total to selective extinction of 4.2, the reddening law applicable to the dust clouds in which the stars are embedded is steeper than normal. The five associations exhibit 18 early-type stars with circumstellar shells, of which those with spectral types earlier than B5 characteristically have weak IR excesses, in contrast to the strong excesses indicative of circumstellar dust, of later-type stars. Color-magnitude charts show a distribution lying above the ZAMS by up to about 2 mag for both the circumstellar shell stars and those classified as rapid rotators. It is suggested that (1) rapid rotation accounts for the scatter in the color-magnitude diagram, and (2) many of the nebulous early-type emission-line stars are rapid rotators rather than pre-main sequence objects.
The Origin of Dust in the Early Universe: Probing the Star Formation History of Galaxies by Their Dust Content
Dwek, Eli; Cherchneff, Isabelle
Two distinct scenarios for the origin of the approximately 4 x 10(exp 8) Solar Mass of dust observed in the high-redshift (z = 6.4) quasar J1148+5251 have been proposed. The first assumes that this galaxy is much younger than the age of the universe at that epoch so that only supernovae, could have produced this dust. The second scenario assumes a significantly older galactic age, so that the dust could have formed in lower-mass AGB stars. Presenting new integral solutions for the chemical evolution of metals and dust in galaxies, we offer a critical evaluation of these two scenarios. ^N;"(,, show that the AGB scenario is sensitive to the details of the galaxy's star formation history (SFH), which must consist of an early intense starburst followed by a period of low stellar activity. The presence or absence of massive amounts of dust in high-redshift galaxies can therefore be used to infer their SFH. However, a problem with the AGB scenario is that it produces a stellar mass that is significantly larger than the inferred dynamical mass of J1148+5251, an yet unresolved discrepancy. If this problem persists, then additional sites for the growth or formation of dust, such as molecular clouds or dense clouds around active galactic nuclei, must be considered.
The helium 10830 A line in early-type stars - An atlas of Fabry-Perot scans
Meisel, D. D.; Frank, Z. A.; Packard, M. L.; Saunders, B. A.
Representative profiles of He I 10830 A in 65 early-type (O6-A1) stars over a wide range of luminosity are presented. The atlas scans were obtained using the Vaughan Fabry-Perot interferometer on the C. E. K. Mees 0.6 m and KPNO 0.9 m telescopes and usually cover a range of plus or minus 15 A at 1 A resolution with sampling distances between 0.5 A and 2 A depending on the photometer integration time required to reach reasonable Poisson counting statistics. The majority of the scans show very shallow, broad features which do not agree with plane-parallel NLTE model atmosphere calculations of the 10830 line by Auer and Mihalas (1972). Difficulties connected with previous theoretical studies of this line are briefly discussed, and suggestions for possible future modifications to the theory are made.
Early spectra of the gravitational wave source GW170817: Evolution of a neutron star merger
Shappee, B. J.; Simon, J. D.; Drout, M. R.; Piro, A. L.; Morrell, N.; Prieto, J. L.; Kasen, D.; Holoien, T. W.-S.; Kollmeier, J. A.; Kelson, D. D.; Coulter, D. A.; Foley, R. J.; Kilpatrick, C. D.; Siebert, M. R.; Madore, B. F.; Murguia-Berthier, A.; Pan, Y.-C.; Prochaska, J. X.; Ramirez-Ruiz, E.; Rest, A.; Adams, C.; Alatalo, K.; Bañados, E.; Baughman, J.; Bernstein, R. A.; Bitsakis, T.; Boutsia, K.; Bravo, J. R.; Di Mille, F.; Higgs, C. R.; Ji, A. P.; Maravelias, G.; Marshall, J. L.; Placco, V. M.; Prieto, G.; Wan, Z.
Two neutron stars merging together generate a gravitational wave signal and have also been predicted to emit electromagnetic radiation. When the gravitational wave event GW170817 was detected, astronomers rushed to search for the source using conventional telescopes (see the Introduction by Smith). Coulter et al. describe how the One-Meter Two-Hemispheres (1M2H) collaboration was the first to locate the electromagnetic source. Drout et al. present the 1M2H measurements of its optical and infrared brightness, and Shappee et al. report their spectroscopy of the event, which is unlike previously detected astronomical transient sources. Kilpatrick et al. show how these observations can be explained by an explosion known as a kilonova, which produces large quantities of heavy elements in nuclear reactions.
Early star catalogues of the southern sky. De Houtman, Kepler (second and third classes), and Halley
Verbunt, F.; van Gent, R. H.
De Houtman in 1603, Kepler in 1627 and Halley in 1679 published the earliest modern catalogues of the southern sky. We provide machine-readable versions of these catalogues, make some comparisons between them, and briefly discuss their accuracy on the basis of comparison with data from the modern Hipparcos Catalogue. We also compare our results for De Houtman with those by Knobel in 1917 finding good overall agreement. About half of the ~ 200 new stars (with respect to Ptolemaios) added by De Houtman are in twelve new constellations, half in old constellations like Centaurus, Lupus and Argo. The right ascensions and declinations given by De Houtman have error distributions with widths of about 40', the longitudes and latitudes given by Kepler have error distributions with widths of about 45'. Halley improves on this by more than an order of magnitude to widths of about 3', and all entries in his catalogue can be identified. The measurement errors of Halley are due to a systematic deviation of his sextant (increasing with angle to 2' at 60°) and random errors of 0.7 arcmin. The position errors in the catalogue of Halley are dominated by the position errors in the reference stars, which he took from Brahe. The full Tables Houtman, Classis, Aliter and Halley (see Tables 6, 7, 8) are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/530/A93
Mid-Infrared Observational and Theoretical Studies of Star Formation and Early Solar Systems
Jones, Barbara
The first 2 years of this program were used to make mid-IR observations of regions of star formation in the Orion nebula with the UCSD mid-IR camera at the UCSD/University of Minnesota telescope at Mt. Lemmon. These observations attempted to make the first systematic study of an extended region, known to have newly forming stars, and expected to have complex mid-IR emission. We discovered, to our surprise, that most of the thermal emission originated from extended sources rather than from point sources. This interesting observation made the analysis of the data much more complex, since the chop/nod procedures used at these wavelengths produce a differential measurement of the emission in one region compared to that in the adjacent region. Disentangling complex extended emission in such a situation is very difficult. In parallel with this work we were also observing comets in the thermal infrared, the other component of the original proposal. Some spectacular data on the comet Swift-Tuttle was acquired and published. A changing jet structure observed over a 2 week period is described. The rotation period of the comet can be measured at 66 hours. The size of the nucleus can also be estimated (at 30 km) from the observed excess flux from the nucleus. These data have lead to the development of models describing the action of dust particles of differing sizes and composition leaving the nucleus. The spatial distribution of the predicted IR emission has been compared to the observed jet structures, leading to estimates of both particles sizes, relative amounts of silicate vs organic grains, and the amounts of dust emitted in the jets vs isotopic emission.
The Planck Catalogue of Galactic Cold Clumps : Looking at the early stages of star-formation
Montier, Ludovic
The Planck satellite has provided an unprecedented view of the submm sky, allowing us to search for the dust emission of Galactic cold sources. Combining Planck-HFI all-sky maps in the high frequency channels with the IRAS map at 100um, we built the Planck catalogue of Galactic Cold Clumps (PGCC, Planck 2015 results XXVIII 2015), counting 13188 sources distributed over the whole sky, and following mainly the Galactic structures at low and intermediate latitudes. This is the first all-sky catalogue of Galactic cold sources obtained with a single instrument at this resolution and sensitivity, which opens a new window on star-formation processes in our Galaxy.I will briefly describe the colour detection method used to extract the Galactic cold sources, i.e., the Cold Core Colour Detection Tool (CoCoCoDeT, Montier et al. 2010), and its application to the Planck data. I will discuss the statistical distribution of the properties of the PGCC sources (in terms of dust temperature, distance, mass, density and luminosity), which illustrates that the PGCC catalogue spans a large variety of environments and objects, from molecular clouds to cold cores, and covers various stages of evolution. The Planck catalogue is a very powerful tool to study the formation and the evolution of prestellar objects and star-forming regions.I will finally present an overview of the Herschel Key Program Galactic Cold Cores (PI. M.Juvela), which allowed us to follow-up about 350 Planck Galactic Cold Clumps, in various stages of evolution and environments. With this program, the nature and the composition of the 5' Planck sources have been revealed at a sub-arcmin resolution, showing very different configurations, such as starless cold cores or multiple Young Stellar objects still embedded in their cold envelope.
Evolution of X-ray activity of 1-3 Msun late-type stars in early post-main-sequence phases
Pizzolato, N.; Maggio, A.; Sciortino, S.
We have investigated the variation of coronal X-ray emission during early post-main-sequence phases for a sample of 120 late-type stars within 100 pc, and with estimated masses in the range 1-3 Msun, based on Hipparcos parallaxes and recent evolutionary models. These stars were observed with the ROSAT/PSPC, and the data processed with the Palermo-CfA pipeline, including detection and evaluation of X-ray fluxes (or upper limits) by means of a wavelet transform algorithm. We have studied the evolutionary history of X-ray luminosity and surface flux for stars in selected mass ranges, including stars with inactive A-type progenitors on the main sequence and lower mass solar-type stars. Our stellar sample suggests a trend of increasing X-ray emission level with age for stars with masses M > 1.5 Msun, and a decline for lower-mass stars. A similar behavior holds for the average coronal temperature, which follows a power-law correlation with the X-ray luminosity, independently of their mass and evolutionary state. We have also studied the relationship between X-ray luminosity and surface rotation rate for stars in the same mass ranges, and how this relationships departs from the Lx ~ vrot2 law followed by main-sequence stars. Our results are interpreted in terms of a magnetic dynamo whose efficiency depends on the stellar evolutionary state through the mass-dependent changes of the stellar internal structure, including the properties of envelope convection and the internal rotation profile.
Exploring X-ray Emission from Winds in Two Early B-type Binary Systems
Rotter, John P.; Hole, Tabetha; Ignace, Richard; Oskinova, Lida
The winds of the most massive (O-type) stars have been well studied, but less is known about the winds of early-type B stars, especially in binaries. Extending O-star wind theory to these smaller stars, we would expect them to emit X-rays, and when in a B-star binary system, the wind collision should emit additional X-rays. This combined X-ray flux from nearby B-star binary systems should be detectable with current telescopes. Yet X-ray observations of two such systems with the Chandra Observatory not only show far less emission than predicted, but also vary significantly from each other despite having very similar observed characteristics. We will present these observations, and our work applying the classic Castor, Abbott, and Klein (CAK) wind theory, combined with more recent analytical wind-shock models, attempting to reproduce this unexpected range of observations.
Tracing early evolutionary stages of high-mass star formation with molecular lines
Marseille, M. G.; van der Tak, F. F. S.; Herpin, F.; Jacq, T.
Context. Despite its major role in the evolution of the interstellar medium, the formation of high-mass stars (M ≥ 10 M_⊙) remains poorly understood. Two types of massive star cluster precursors, the so-called massive dense cores (MDCs), have been observed, which differ in terms of their mid-infrared brightness. The origin of this difference has not yet been established and may be the result of evolution, density, geometry differences, or a combination of these. Aims: We compare several molecular tracers of physical conditions (hot cores, shocks) observed in a sample of mid-IR weakly emitting MDCs with previous results obtained in a sample of exclusively mid-IR bright MDCs. We attempt to understand the differences between these two types of object. Methods: We present single-dish observations of HDO, H_218O, SO2, and CH3OH lines at λ = 1.3-3.5 mm. We study line profiles and estimate abundances of these molecules, and use a partial correlation method to search for trends in the results. Results: The detection rates of thermal emission lines are found to be very similar for both mid-IR quiet and bright objects. The abundances of H2O, HDO (10-13 to 10-9 in the cold outer envelopes), SO2 and CH3OH differ from source to source but independently of their mid-IR flux. In contrast, the methanol class I maser emission, a tracer of outflow shocks, is found to be strongly anti-correlated with the 12 μm source brightnesses. Conclusions: The enhancement of the methanol maser emission in mid-IR quiet MDCs may be indicative of a more embedded nature. Since total masses are similar between the two samples, we suggest that the matter distribution is spherical around mid-IR quiet sources but flattened around mid-IR bright ones. In contrast, water emission is associated with objects containing a hot molecular core, irrespective of their mid-IR brightness. These results indicate that the mid-IR brightness of MDCs is an indicator of their evolutionary stage.
The evolution of surface magnetic fields in young solar-type stars II: the early main sequence (250-650 Myr)
Folsom, C. P.; Bouvier, J.; Petit, P.; Lèbre, A.; Amard, L.; Palacios, A.; Morin, J.; Donati, J.-F.; Vidotto, A. A.
There is a large change in surface rotation rates of sun-like stars on the pre-main sequence and early main sequence. Since these stars have dynamo-driven magnetic fields, this implies a strong evolution of their magnetic properties over this time period. The spin-down of these stars is controlled by interactions between stellar and magnetic fields, thus magnetic evolution in turn plays an important role in rotational evolution. We present here the second part of a study investigating the evolution of large-scale surface magnetic fields in this critical time period. We observed stars in open clusters and stellar associations with known ages between 120 and 650 Myr, and used spectropolarimetry and Zeeman Doppler Imaging to characterize their large-scale magnetic field strength and geometry. We report 15 stars with magnetic detections here. These stars have masses from 0.8 to 0.95 M⊙, rotation periods from 0.326 to 10.6 d, and we find large-scale magnetic field strengths from 8.5 to 195 G with a wide range of geometries. We find a clear trend towards decreasing magnetic field strength with age, and a power law decrease in magnetic field strength with Rossby number. There is some tentative evidence for saturation of the large-scale magnetic field strength at Rossby numbers below 0.1, although the saturation point is not yet well defined. Comparing to younger classical T Tauri stars, we support the hypothesis that differences in internal structure produce large differences in observed magnetic fields, however for weak-lined T Tauri stars this is less clear.
Studies of early-type variable stars. XIV. Spectroscopic orbit and absolute parameters of HU Tauri.
Maxted, P. F. L.; Hill, G.; Hilditch, R. W.
We present a new spectroscopic orbit for the Algol-type eclipsing binary system HU Tau (HD 29365, P=2.0563 days α(2000.0) = 04 38 15.80, δ= +20 41 05.3, V=5.87-6.8, B8V + G2). We find : m_1_ sin^3^i=4.17+/-0.09Msun_, m_2_ sin^3^i=1.07+/-0.025Msun_, (a_p_+a_s_)sin i=11.8 +/-0.1Rsun_, m_1_/m_2_=3.90+/-0.07. The spectroscopic orbit includes corrections for non-Keplerian effects derived from the solutions of the BV light curves of Ito (1988). We have been able to derive much improved absolute parameters for this system as follows: M_1_=4.43+/-0.09Msun_, M_2_=1.14+/-0.03Msun_, R _1_=2.57+/-0.03Rsun_, R _2_=4.21+/-0.03Rsun_, log(L_1_/Lsun_)= 2.09+/-0.15, log(L_2_/Lsun_)= 0.92+/-0.05. Comparison of HU Tau with non-conservative case B evolution models of De Greve (1993) suggests that the system evolved from an initial mass ratio <~0.5. However, the orbital period of HU Tau is more than 3 days shorter than any of the model systems, and the observed secondary luminosity of order 10 times less than a model star of the same mass during the slow mass transfer phase.
The Massive Star Content of NGC 3603
Melena, Nicholas W.; Massey, Philip; Morrell, Nidia I.; Zangari, Amanda M.
We investigate the massive star content of NGC 3603, the closest known giant H II region. We have obtained spectra of 26 stars in the central cluster using the Baade 6.5 m telescope (Magellan I). Of these 26 stars, 16 had no previous spectroscopy. We also obtained photometry of all of the stars with previous or new spectroscopy, primarily using archival HST Advanced Camera for Surveys/High-Resolution Camera images. The total number of stars that have been spectroscopically classified in NGC 3603 now stands at 38. The sample is dominated by very early O-type stars (O3); there are also several (previously identified) H-rich WN+abs stars. We derive E(B - V) = 1.39, and find that there is very little variation in reddening across the cluster core, in agreement with previous studies. Our spectroscopic parallax is consistent with the kinematic distance only if the ratio of total to selective extinction is anomalously high within the cluster, as argued by Pandey et al. Adopting their reddening, we derive a distance of 7.6 kpc. We discuss the various distance estimates to the cluster, and note that although there has been a wide range of values in the recent literature (6.3-10.1 kpc) there is actually good agreement with the apparent distance modulus of the cluster—the disagreement has been the result of the uncertain reddening correction. We construct our H-R diagram using the apparent distance modulus with a correction for the slight difference in differential reddening from star to star. The resulting H-R diagram reveals that the most massive stars are highly coeval, with an age of 1-2 Myr, and of very high masses (120 Msun). The three stars with Wolf-Rayet features are the most luminous and massive, and are coeval with the non-WRs, in accord with what was found in the R136 cluster. There may be a larger age spread (1-4 Myr) for the lower mass objects (20-40 Msun). Two supergiants (an OC9.7 I and the B1 I star Sher 25) both have an age of about 4 Myr. We compare the
From red star rising to rocket's red glare: space travel, the early years
Chapman, Steven
'We choose to go to the Moon in this decade and do the other things, not because they are easy, but because they are hard, because that goal will serve to organize and measure the best of our energies and skills, because that challenge is one that we are willing to accept, one we are unwilling to postpone, and one which we intend to win, and the others, too.' President John Fitzgerald Kennedy, 12 September 1962. It is now 50 years since the first artificial satellite was launched. This article looks at the early years of space travel and some of the key moments during that time.
Exploring new classification criteria for the earliest type stars: the 3400 Aregion
Morrell, Nidia I.; Walborn, Nolan R.; Arias, Julia I.
We propose spectroscopic observations of a sample of standard O2-O4 stars in the wavelength region containing the N IV 3479-83-85 Aand O IV 3381-85-3412 Alines, in order to analyze the behavior of these spectral features as a function of the spectral type. We aim to define new classification criteria for the hottest stars, evaluating these N IV and O IV lines near 3400 Aas possible temperature and luminosity discriminators. The former spectral class O3 has just been split into three different classes: O2, O3 and O3.5 (Walborn et al. 2001). The paucity of classification criteria at these types in the traditional wavelength domain (4000 - 4700 Ã…), makes clear the need to explore other spectral ranges in order to define additional constraints on the determination of spectral types and luminosity classes. The wavelength range around 3400 Ahas been observed in many faint, crowded early O-type stars by HST/FOS, the corresponding data being available from the HST archive. This enhances our interest in observing this spectral range in the classification standards for the early O-type stars in order to make these existing HST observations even more useful, allowing the determination of accurate spectral types for unknown objects from them, once the behavior of the new criteria in the standards has been charted.
Interstellar C IV and Si IV column densities toward early-type stars
Bruhweiler, F. C.; Kondo, Y.; Mccluskey, G. E.
Equivalent widths and deduced column densities of Si IV and C IV are examined for 18 early-type close binaries, and physical processes responsible for the origin of these ions in the interstellar medium are investigated. The available C IV/Si IV column density ratios typically lie within a narrow range from 0.8 to 4.5, and there is evidence that the column density of C IV is higher than that of N V along most lines of sight, suggesting that C IV is not formed in the same hot region as O VI. In addition, the existence of regions with a narrowly defined new temperature range around 50,000 deg K is indicated. The detection of the semitorrid gas of Bruhweiler, Kondo, and McCluskey (1978, 1979) is substantiated, and the relation of this gas to the observations of coronal gas in the galactic halo is discussed.
The stars and the state: Astronomy, astrology, and the politics of natural knowledge in early medieval Japan
Buhrman, Kristina Mairi
This dissertation examines the social factors involved in the practices of observational astrology (Ch. tianwen, Jp. tenmon ) and calendrical astronomy (Ch. lifa, Jp. rekih�) at the Japanese court. The production and monopolization of astrological and astronomical knowledge had, from the time of the Han Dynasty in China, been part of the state bureaucracy and one of the signs of legitimate rule. In the seventh century, Japan too had imported and implemented these state sciences of the Chinese-style imperium. However, by the twelfth century, while state control of astronomical knowledge continued to operate at a surface level, within the Japanese court bureaucracy dissent and debate reigned. A number of lineages and factions cooperated or competed over astronomical and astrological facts, which resulted in a situation where there was no unified "truth" about the stars accepted by the majority of elite members of the court. The political fragmentation and factionalism that characterized the early medieval Japanese state was also to be found in knowledge about the natural world circulating at court. The major reason for this fragmentation of knowledge was the diversity of the population that produced this same knowledge, a population that did not share either a common identity or definition of practice. Astrological and astronomical knowledge was no longer produced solely by the technical bureaucrats whose offices had been established in the eighth-century Chinese-style law codes (Jp. ritsury�)—instead, these officials contested with other legitimate but non-official purveyors of natural knowledge: Buddhist monks and court scholars and mathematicians prominent among them. Furthermore, the statements of fact produced by all three of these factions were subject to critique and revision by members of the top echelon of the court bureaucracy, the elite nobility. Clearly there were no
Effective temperatures and luminosities of very hot o-type subdwarfs
Schoenberner, D.; Drilling, J. S.
Twelve very hot O-type subdwarfs were observed with the IUE-satellite in the low dispersion mode. Temperatures were derived from the slopes of the UV continua and distances were estimated from the color excesses. Most of them are hotter than 60,000 K, i.e., they are the hottest known subdwarfs. From their spectral appearance and location in a H.R.-diagram they form a rather inhomogeneous group. Three of them turned out to be central stars or nearly central stars, and four are definitely near the white dwarf stage. The surface helium to hydrogen ratio varies from about normal to the extreme case. Most of them appear to be post EHB objectives of 0.5 solar mass with a helium burning shell as their energy source, and their peculiar helium-to-hydrogen ratios are most likely the result of diffusion and convective mixing in surface layers.
Using ALMA to Resolve the Nature of the Early Star-Forming Large-Scale Structure G073
Hill, R.; Kneissl, R.; Polletta, M.; Clarenc, B.; Dole, H. A.; Nesvadba, N. P. H.; Scott, D.; Béthermin, M.; Lagache, G.; Montier, L.
Galaxy clusters at large redshift are key targets for understanding the nature of the early Universe, yet locating them has proven to be very challenging. Recently, a large sample of over 2000 high-z candidate structures have been found using Planck's all-sky submillimetre maps, and a subset of 234 have been followed up with Herschel-SPIRE, which showed that the emission can be attributed to large far-infrared overdensities. However, the individual galaxies giving rise to the emission seen by Planck and Herschel have not yet been resolved nor characterized, so we do not yet know whether these sources are the progenitors of present-day, massive galaxy clusters. In an attempt to address this, we targeted the eight brightest Herschel-SPIRE peaks in the centre of the Planck peak G073.4-57.5 using ALMA at 1.3 mm, and complemented these observations with multi-wavelength data from Spitzer-IRAC at 3.6 and 4.5 μm and from CFHT-WIRCam at 1.2 and 2.2 μm. We also utilize data on G073.4-57.5 at 850 μm from JCMT's SCUBA-2 instrument. We detect a total of 18 millimetre galaxies brighter than 0.3mJy in 2.4arcmin2. In every case we are able to match these to their NIR counterparts, and while the most significant SCUBA-2 sources are not included in the ALMA pointings, we find an 8σ detection when stacking the ALMA source positions in the 850 μm data. We derive photometric redshifts, IR luminosities, star-formation rates, stellar masses, dust temperatures, and dust masses; the photometric redshifts are concentrated around z ≃ 1 and z ≃ 2 and the NIR colours show a "red" sequence, while the star-formation rates indicate that three of the galaxies are "starbursts". Serendipitous CO line detections of two of the galaxies appear to match their photometric redshifts with z = 2.05. We find that the ALMA source density is 8-30 times higher than average background estimates, and thus also larger than seen in typical "proto-cluster" fields. The evidence seems to be indicating the
The Role of Rotation in the Evolution of Massive Stars
Heap, Sara R.; Lanz, Thierry M.
Recent evolutionary models of massive stars predict important effects of rotation including: increasing the rate of mass loss; lowering the effective gravity; altering the evolutionary track on the Hertzsprung-Russel Diagram (HRD); extending the main-sequence phase (both on the HR diagram and in time); and mixing of CNO-processed elements up to the stellar surface. Observations suggest that rotation is a more important factor at lower metallicities because of higher initial rotational velocities and weaker winds. This makes the Small Magellanic Cloud (SMC), a low-metallicity galaxy (Z=0.2 solar Z), an excellent environment for discerning the role of rotation in massive stars. We report on a FUSE+STIS+optical spectral analysis of 17 O-type stars in the SMC, where we found an enormous range in N abundances. Three stars in the sample have the same (low) CN abundances as the nebular material out of which they formed, namely C=0.085 solar C and N=0.034 solar N. However, more than half show N approx. solar N, an enrichment factor of 30X! Such unexpectedly high levels of N have ramifications for the evolution of massive stars including precursors to supernovae. They also raise questions about the sources of nitrogen in the early universe. This study was supported in part by grants from NASA's ADP, HST GO-7437, and FUSE B134.
Recent evolutionary models of massive stars predict important effects of rotation including: increasing the rate of mass-loss; lowering the effective gravity; altering the evolutionary track on the HRD; extending the main-sequence phase (both on the HR diagram and in time); and mixing of CNO-processed elements up to the stellar surface. Observations suggest that rotation is a more important factor at lower metallicities because of higher initial rotational velocities and weaker winds. This makes the SMC, a low-metallicity galaxy (Z= 0.2 solar Z), an excellent environment for discerning the role of rotation in massive stars. We report on a FUSE + STIS + optical spectral analysis of 17 O-type stars in the SMC, where we found an enormous range in N abundances. Three stars in the sample have the same (low) CN abundances as the nebular material out of which they formed, namely C = 0.085 solar C and N = 0.034 solar N. However, more than half show N approx. solar N, an enrichment factor of 30X! Such unexpectedly high levels of N have ramifications for the evolution of massive stars including precursors to supernovae. They also raise questions about the sources of nitrogen in the early universe.
Constraining the Fundamental Parameters of the O-Type Binary CPD -41 7733
Sana, H.; Rauw, G.; Gosset, E.
Using a set of high-resolution spectra, we studied the physical and orbital properties of the O-type binary CPD -41 7733, located in the core of NGC 6231. We report the unambiguous detection of a secondary spectral signature and we derive the first SB2 orbital solution of the system. The period is 5.6815+/-0.0015 days, and the orbit has no significant eccentricity. CPD -41 7733 probably consists of stars of spectral types O8.5 and B3. As for other objects in the cluster, we observe discrepant luminosity classifications while using spectroscopic or brightness criteria. Still, the present analysis suggests that both components display physical parameters close to those of typical O8.5 and B3 dwarfs. We also analyze the X-ray light curves and spectra obtained during six 30 ks XMM-Newton pointings spread over the 5.7 day period. We find no significant variability between the different pointings, nor within the individual observations. The CPD -41 7733 X-ray spectrum is well reproduced by a three-temperature thermal mekal model with temperatures of 0.3, 0.8, and 2.4 keV. No X-ray overluminosity, resulting, e.g., from a possible wind interaction, is observed. The emission of CPD -41 7733 is thus very representative of typical O-type star X-ray emission.
Evolution of solitary density waves in stellar winds of early-type stars: A simple explanation of discrete absorption component behavior
Waldron, Wayne L.; Klein, Larry; Altner, Bruce
We model the evolution of a density shell propagating through the stellar wind of an early-type star, in order to investigate the effects of such shells on UV P Cygni line profiles. Unlike previous treatments, we solve the mass, momentum, and energy conservation equations, using an explicit time-differencing scheme, and present a parametric study of the density, velocity, and temperature response. Under the assumed conditions, relatively large spatial scale, large-amplitude density shells propagate as stable waves through the supersonic portion of the wind. Their dynamical behavior appears to mimic propagating 'solitary waves,' and they are found to accelerate at the same rate as the underlying steady state stellar wind (i.e., the shell rides the wind). These hydrodynamically stable structures quantitatively reproduce the anomalous 'discrete absorption component' (DAC) behavior observed in the winds of luminous early-type stars, as illustrated by comparisons of model predictions to an extensive International Ultraviolet Explorer (IUE) time series of spectra of zeta Puppis (O4f). From these comparisons, we find no conclusive evidence indicative of DACs accelerating at a significantly slower rate than the underlying stellar wind, contrary to earlier reports. In addition, these density shells are found to be consistent within the constraints set by the IR observations. We conclude that the concept of propagating density shells should be seriously reconsidered as a possible explanation of the DAC phenomenon in early-type stars.
Chemical Composition of Galactic Disk Stars
Mishenina, T. V.; Basak, N. Yu.; Gorbaneva, T. I.; Soubiran, C.; Kovtyukh, V. V.
Abundances of Na, Al, Ca, in the stars of galactic disks are obtained. The separation of thin and stars on cinematic criterion was made early. The behavior of chemical element abundances with metallicity for studied stars was presented.
The Peculiarities in O-Type Galaxy Clusters
Panko, E. A.; Emelyanov, S. I.
We present the results of analysis of 2D distribution of galaxies in galaxy cluster fields. The Catalogue of Galaxy Clusters and Groups PF (Panko & Flin) was used as input observational data set. We selected open rich PF galaxy clusters, containing 100 and more galaxies for our study. According to Panko classification scheme open galaxy clusters (O-type) have no concentration to the cluster center. The data set contains both pure O-type clusters and O-type clusters with overdence belts, namely OL and OF types. According to Rood & Sastry and Struble & Rood ideas, the open galaxy clusters are the beginning stage of cluster evolution. We found in the O-type clusters some types of statistically significant regular peculiarities, such as two crossed belts or curved strip. We suppose founded features connected with galaxy clusters evolution and the distribution of DM inside the clusters.
Elvis to Eminem: quantifying the price of fame through early mortality of European and North American rock and pop stars.
Bellis, Mark A; Hennell, Tom; Lushey, Clare; Hughes, Karen; Tocque, Karen; Ashton, John R
Rock and pop stars are frequently characterised as indulging in high-risk behaviours, with high-profile deaths amongst such musicians creating an impression of premature mortality. However, studies to date have not quantified differences between mortality experienced by such stars and general populations. This study measures survival rates of famous musicians (n = 1064) from their point of fame and compares them to matched general populations in North America and Europe. We describe and utilise a novel actuarial survival methodology which allows quantification of excess post-fame mortality in pop stars. Individuals from North America and Europe performing on any album in the All-Time Top 1000 albums from the music genres rock, punk, rap, R&B, electronica and new age. From 3 to 25 years post fame, both North American and European pop stars experience significantly higher mortality (more than 1.7 times) than demographically matched populations in the USA and UK, respectively. After 25 years of fame, relative mortality in European (but not North American) pop stars begins to return to population levels. Five-year post-fame survival rates suggest differential mortality between stars and general populations was greater in those reaching fame before 1980. Pop stars can suffer high levels of stress in environments where alcohol and drugs are widely available, leading to health-damaging risk behaviour. However, their behaviour can also influence would-be stars and devoted fans. Collaborations between health and music industries should focus on improving both pop star health and their image as role models to wider populations.
Elvis to Eminem: quantifying the price of fame through early mortality of European and North American rock and pop stars
Background Rock and pop stars are frequently characterised as indulging in high�risk behaviours, with high�profile deaths amongst such musicians creating an impression of premature mortality. However, studies to date have not quantified differences between mortality experienced by such stars and general populations. Objective This study measures survival rates of famous musicians (n = 1064) from their point of fame and compares them to matched general populations in North America and Europe. Design We describe and utilise a novel actuarial survival methodology which allows quantification of excess post�fame mortality in pop stars. Participants Individuals from North America and Europe performing on any album in the All�Time Top 1000 albums from the music genres rock, punk, rap, R&B, electronica and new age. Results From 3 to 25 years post fame, both North American and European pop stars experience significantly higher mortality (more than 1.7 times) than demographically matched populations in the USA and UK, respectively. After 25 years of fame, relative mortality in European (but not North American) pop stars begins to return to population levels. Five�year post�fame survival rates suggest differential mortality between stars and general populations was greater in those reaching fame before 1980. Conclusion Pop stars can suffer high levels of stress in environments where alcohol and drugs are widely available, leading to health�damaging risk behaviour. However, their behaviour can also influence would�be stars and devoted fans. Collaborations between health and music industries should focus on improving both pop star health and their image as role models to wider populations. PMID:17873227
Light Chemical Elements in Stars: Mysteries and Unsolved Problems
Lyubimkov, L. S.
The first eight elements of the periodic table are discussed: H, He, Li, Be, B, C, N, and O. They are referred to as key elements, given their important role in stellar evolution. It is noteworthy that all of them were initially synthesized in the Big Bang. The primordial abundances of these elements calculated using the Standard Model of the Big Bang (SMBB) are presented in this review. The good agreement between the SMBB and observations of the primordial abundances of the isotopes of hydrogen and helium, D, 3He, and 4He, is noted, but there is a difference of 0.5 dex for lithium (the isotope 7Li) between the SMBB and observations of old stars in the galactic halo that has not yet been explained. The abundances of light elements in stellar atmospheres depends on the initial rotation velocity, so the typical rotation velocities of young Main Sequence (MS) stars are examined. Since the data on the abundances of light elements in stars are very extensive, the main emphasis in this review is on several unsolved problems. The helium abundance He/H in early B-type of the MS stars shows an increment with age; in particular, for the most massive B stars with masses M = 12-19M ⊙, He/H increases by more than a factor of two toward the end of the MS. Theoretical models of stars with rotation cannot explain such a large increase in He/H. For early B- and late O-type MS stars that are components of close binary systems, He/H undergoes a sharp jump in the middle of the MS stage that is a mystery for the theory. The anomalous abundance of helium (and lithium) in the atmospheres of chemically peculiar stars (types He-s, He-w, HgMn, Ap, and Am) is explained in terms of the diffusion of atoms in surface layers of the stars, but this hypothesis cannot yet explain all the features of the chemical composition of these stars. The abundances of lithium, beryllium, and boron in FGK-dwarfs manifest a trend with decreasing effective temperature T eff as well as a dip at T eff 6600 K in
EPISODIC ACCRETION AT EARLY STAGES OF EVOLUTION OF LOW-MASS STARS AND BROWN DWARFS: A SOLUTION FOR THE OBSERVED LUMINOSITY SPREAD IN H-R DIAGRAMS?
Baraffe, I.; Chabrier, G.; Gallardo, J.
We present evolutionary models for young low-mass stars and brown dwarfs taking into account episodic phases of accretion at early stages of the evolution, a scenario supported by recent large surveys of embedded protostars. An evolution including short episodes of vigorous accretion followed by longer quiescent phases can explain the observed luminosity spread in H-R diagrams of star-forming regions at ages of a few Myr, for objects ranging from a few Jupiter masses to a few tenths of a solar mass. The gravitational contraction of these accreting objects strongly departs from the standard Hayashi track at constant T{sub eff}. Themore » best agreement with the observed luminosity scatter is obtained if most of the accretion shock energy is radiated away. The obtained luminosity spread at 1 Myr in the H-R diagram is equivalent to what can be misinterpreted as an {approx}10 Myr age spread for non-accreting objects. We also predict a significant spread in radius at a given T{sub eff}, as suggested by recent observations. These calculations bear important consequences for our understanding of star formation and early stages of evolution and on the determination of the initial mass function for young ({<=} a few Myr) clusters. Our results also show that the concept of a stellar birthline for low-mass objects has no valid support.« less
OB stars at the lowest Local Group metallicity. GTC-OSIRIS observations of Sextans A
Camacho, I.; Garcia, M.; Herrero, A.; Simón-Díaz, S.
Context. Massive stars play an important role in the chemical and dynamical evolution of the Universe. The first metal-poor stars may have started the reionization of the Universe. To understand these early epochs it is necessary to know the behavior and the physical properties of massive stars in very metal-poor environments. We focus on the massive stellar content of the metal-poor irregular galaxy Sextans A. Aims: Our aim is to find and classify OB stars in Sextans A, so as to later determine accurate stellar parameters of these blue massive stars in this low-metallicity region (Z ~ 0.1 Z⊙). Methods: Using UBV photometry, the reddening-free index Q and GALEX imaging, we built a list of blue massive star candidates in Sextans A. We obtained low-resolution (R ~ 1000) GTC-OSIRIS spectra for a fraction of them and carried out spectral classification. For the confirmed O-stars, we derived preliminary stellar parameters. Results: The target selection criteria and observations were successful and have produced the first spectroscopic atlas of OB-type stars in Sextans A. From the whole sample of 18 observed stars, 12 were classified as early OB-types, including 5 O-stars. The radial velocities of all target stars are in agreement with their Sextans A membership, although three of them show significant deviations. We determined the stellar parameters of the O-type stars using the stellar atmosphere code FASTWIND and revisited the sub-SMC temperature scale. Two of the O-stars are consistent with relatively strong winds and enhanced helium abundances, although results are not conclusive. We discuss the position of the OB stars in the HRD. Initial stellar masses run from slightly below 20 up to 40 solar masses. Conclusions: The target selection method worked well for Sextans A. The stellar temperatures are consistent with findings in other galaxies. Some of the targets deserve follow-up spectroscopy because of indications of a runaway nature, an enhanced helium abundance
Two spotted and magnetic early B-type stars in the young open cluster NGC 2264 discovered by MOST and ESPaDOnS
Fossati, L.; Zwintz, K.; Castro, N.; Langer, N.; Lorenz, D.; Schneider, F. R. N.; Kuschnig, R.; Matthews, J. M.; Alecian, E.; Wade, G. A.; Barnes, T. G.; Thoul, A. A.
Star clusters are known as superb tools for understanding stellar evolution. In a quest for understanding the physical origin of magnetism and chemical peculiarity in about 7% of the massive main-sequence stars, we analysed two of the ten brightest members of the ~10 Myr old Galactic open cluster NGC 2264, the early B-dwarfs HD 47887 and HD 47777. We find accurate rotation periods of 1.95 and 2.64 days, respectively, from MOST photometry. We obtained ESPaDOnS spectropolarimetric observations, through which we determined stellar parameters, detailed chemical surface abundances, projected rotational velocities, and the inclination angles of the rotation axis. Because we found only small (<5 km s-1) radial velocity variations, most likely caused by spots, we can rule out that HD 47887 and HD 47777 are close binaries. Finally, using the least-squares deconvolution technique, we found that both stars possess a large-scale magnetic field with an average longitudinal field strength of about 400 G. From a simultaneous fit of the stellar parameters we determine the evolutionary masses of HD 47887 and HD 47777 to be 9.4+0.6-0.7 M⊙ and 7.6+0.5-0.5 M⊙. Interestingly, HD 47777 shows a remarkable helium underabundance, typical of helium-weak chemically peculiar stars, while the abundances of HD 47887 are normal, which might imply that diffusion is operating in the lower mass star but not in the slightly more massive one. Furthermore, we argue that the rather slow rotation, as well as the lack of nitrogen enrichment in both stars, can be consistent with both the fossil and the binary hypothesis for the origin of the magnetic field. However, the presence of two magnetic and apparently single stars near the top of the cluster mass-function may speak in favour of the latter. Based on data from the MOST satellite, a Canadian Space Agency mission, jointly operated by Microsatellite Systems Canada Inc. (MSCI), formerly part of Dynacon, Inc., the University of Toronto Institute for
Modeling the early evolution of massive OB stars with an experimental wind routine. The first bi-stability jump and the angular momentum loss problem
Keszthelyi, Z.; Puls, J.; Wade, G. A.
Context. Stellar evolution models of massive stars are very sensitive to the adopted mass-loss scheme. The magnitude and evolution of mass-loss rates significantly affect the main sequence evolution, and the properties of post-main sequence objects, including their rotational velocities. Aims: Driven by potential discrepancies between theoretically predicted and observationally derived mass-loss rates in the OB star range, we aim in particular to investigate the response to mass-loss rates that are lower than currently adopted, in parallel with the mass-loss behavior at the "first" bi-stability jump. Methods: We performed 1D hydrodynamical model calculations of single 20-60 M⊙ Galactic (Z = 0.014) stars where the effects of stellar winds are already significant in the main sequence phase. We have developed an experimental wind routine to examine the behavior and response of the models under the influence of different mass-loss rates. This observationally guided, simple and flexible wind routine is not a new mass-loss description but a useful tool based on the wind-momentum luminosity relation and other scaling relations, and provides a meaningful base for various tests and comparisons. Results: The main result of this study indicates a dichotomy between solutions of currently debated problems regarding mass-loss rates of hot massive stars. In a fully diffusive approach, and for commonly adopted initial rotational velocities, lower mass-loss rates than theoretically predicted require to invoke an additional source of angular momentum loss (either due to bi-stability braking, or yet unidentified) to brake down surface rotational velocities. On the other hand, a large jump in the mass-loss rates due to the bi-stability mechanism (a factor of 5-7 predicted by Vink et al. (2000, A&A, 362, 295), but a factor of 10-20 in modern models of massive stars) is challenged by observational results, and might be avoided if the early mass-loss rates agreed with the theoretically
Nitrogen line spectroscopy of O-stars. II. Surface nitrogen abundances for O-stars in the Large Magellanic Cloud
Rivero González, J. G.; Puls, J.; Najarro, F.; Brott, I.
Context. Nitrogen is a key element for testing the impact of rotational mixing on evolutionary models of massive stars. Recent studies of the nitrogen surface abundance in B-type stars within the VLT-FLAMES survey of massive stars have challenged part of the corresponding predictions. To obtain a more complete picture of massive star evolution, and to allow for additional constraints, these studies need to be extended to O-stars. Aims: This is the second paper in a series aiming at the analysis of nitrogen abundances in O-type stars, to establish tighter constraints on the early evolution of massive stars. In this paper, we investigate the N ivλ4058 emission line formation, provide nitrogen abundances for a substantial O-star sample in the Large Magellanic Cloud, and compare our (preliminary) findings with recent predictions from stellar evolutionary models. Methods: Stellar and wind parameters of our sample stars were determined by line profile fitting of hydrogen, helium and nitrogen lines, exploiting the corresponding ionization equilibria. Synthetic spectra were calculated by means of the NLTE atmosphere/spectrum synthesis code fastwind, using a new nitrogen model atom. We derived nitrogen abundances for 20 O- and 5 B-stars by analyzing all nitrogen lines (from different ionization stages) present in the available optical spectra. Results: The dominating process responsible for emission at N ivλ4058 in O-stars is the strong depopulation of the lower level of the transition, which increases as a function of Ṁ. Unlike the N iii triplet emission, resonance lines do not play a role for typical mass-loss rates and below. We find (almost) no problem in fitting the nitrogen lines, in particular the "f" features. Only for some objects, where lines from N iii/N iv/N v are visible in parallel, we need to opt for a compromise solution. For five objects in the early B-/late O-star domain that have been previously analyzed by different methods and model atmospheres, we
Empirical ionization fractions in the winds and the determination of mass-loss rates for early-type stars
Lamers, H. J. G. L. M.; Gathier, R.; Snow, T. P.
From a study of the UV lines in the spectra of 25 stars from 04 to B1, the empirical relations between the mean density in the wind and the ionization fractions of O VI, N V, Si IV, and the excited C III (2p 3P0) level were derived. Using these empirical relations, a simple relation was derived between the mass-loss rate and the column density of any of these four ions. This relation can be used for a simple determination of the mass-loss rate from O4 to B1 stars.
Non-LTE, line-blanketed model atmospheres for late O- and early B-type stars
Grigsby, James A.; Morrison, Nancy D.; Anderson, Lawrence S.
The use of non-LTE line-blanketed model atmospheres to analyze the spectra of hot stars is reported. The stars analyzed are members of clusters and associations, have spectral types in the range O9-B2 and luminosity classes in the range III-IV, have slow to moderate rotation, and are photometrically constant. Sampled line opacities of iron-group elements were incorporated in the radiative transfer solution; solar abundances were assumed. Good to excellent agreement is obtained between the computed profiles and essentially all the line profiles used to fix the model, and reliable stellar parameters are derived. The synthetic M II 5581 equivalent widths agree well with the observed ones at the low end of the temperature range studied, but, above 25,000 K, the synthetic line is generally stronger than the observed line. The behavior of the observed equivalent widths of N II, N III, C II and C III lines as a function of Teff is studied. Most of the lines show much scatter, with no consistent trend that could indicate abundance differences from star to star.
Dark stars: a review.
Freese, Katherine; Rindler-Daller, Tanja; Spolyar, Douglas; Valluri, Monica
Dark stars are stellar objects made (almost entirely) of hydrogen and helium, but powered by the heat from dark matter annihilation, rather than by fusion. They are in hydrostatic and thermal equilibrium, but with an unusual power source. Weakly interacting massive particles (WIMPs), among the best candidates for dark matter, can be their own antimatter and can annihilate inside the star, thereby providing a heat source. Although dark matter constitutes only [Formula: see text]0.1% of the stellar mass, this amount is sufficient to power the star for millions to billions of years. Thus, the first phase of stellar evolution in the history of the Universe may have been dark stars. We review how dark stars come into existence, how they grow as long as dark matter fuel persists, and their stellar structure and evolution. The studies were done in two different ways, first assuming polytropic interiors and more recently using the MESA stellar evolution code; the basic results are the same. Dark stars are giant, puffy (∼10 AU) and cool (surface temperatures  ∼10 000 K) objects. We follow the evolution of dark stars from their inception at  ∼[Formula: see text] as they accrete mass from their surroundings to become supermassive stars, some even reaching masses  >[Formula: see text] and luminosities  >[Formula: see text], making them detectable with the upcoming James Webb Space Telescope. Once the dark matter runs out and the dark star dies, it may collapse to a black hole; thus dark stars may provide seeds for the supermassive black holes observed throughout the Universe and at early times. Other sites for dark star formation may exist in the Universe today in regions of high dark matter density such as the centers of galaxies. The current review briefly discusses dark stars existing today, but focuses on the early generation of dark stars.
Dark stars: a review
Dark stars are stellar objects made (almost entirely) of hydrogen and helium, but powered by the heat from dark matter annihilation, rather than by fusion. They are in hydrostatic and thermal equilibrium, but with an unusual power source. Weakly interacting massive particles (WIMPs), among the best candidates for dark matter, can be their own antimatter and can annihilate inside the star, thereby providing a heat source. Although dark matter constitutes only ≲ 0.1% of the stellar mass, this amount is sufficient to power the star for millions to billions of years. Thus, the first phase of stellar evolution in the history of the Universe may have been dark stars. We review how dark stars come into existence, how they grow as long as dark matter fuel persists, and their stellar structure and evolution. The studies were done in two different ways, first assuming polytropic interiors and more recently using the MESA stellar evolution code; the basic results are the same. Dark stars are giant, puffy (˜10 AU) and cool (surface temperatures  ˜10 000 K) objects. We follow the evolution of dark stars from their inception at  ˜1{{M}⊙} as they accrete mass from their surroundings to become supermassive stars, some even reaching masses  >{{10}6}{{M}⊙} and luminosities  >{{10}10}{{L}⊙} , making them detectable with the upcoming James Webb Space Telescope. Once the dark matter runs out and the dark star dies, it may collapse to a black hole; thus dark stars may provide seeds for the supermassive black holes observed throughout the Universe and at early times. Other sites for dark star formation may exist in the Universe today in regions of high dark matter density such as the centers of galaxies. The current review briefly discusses dark stars existing today, but focuses on the early generation of dark stars.
High S/N Echelle spectroscopy in young stellar groups. II. Rotational velocities of early-type stars in SCO OB2.
Brown, A. G. A.; Verschueren, W.
We investigate the rotational velocities of early-type stars in the Sco OB2 association. We measure v.sin(i) for 156 established and probable members of the association. The measurements are performed with three different techniques, which are in increasing order of expected v.sin(i): 1) converting the widths of spectral lines directly to v.sin(i), 2) comparing artificially broadened spectra of low v.sin(i) stars to the target spectrum, 3) comparing the HeI λ4026 line profile to theoretical models. The sample is extended with literature data for 47 established members of Sco OB2. Analysis of the v.sin(i) distributions shows that there are no significant differences between the subgroups of Sco OB2. We find that members of the binary population of Sco OB2 on the whole rotate more slowly than the single stars. In addition, we find that the B7-B9 single star members rotate significantly faster than their B0-B6 counterparts. We test various hypotheses for the distribution of v.sin(i) in the association. The results show that we cannot clearly exclude any form of random distribution of the direction and/or magnitude of the intrinsic rotational velocity vector. We also investigate the effects of rotation on colours in the Walraven photometric system. We show that positions of B7-B9 single dwarfs above the main sequence are a consequence of rotation. This establishes the influence of rotation on the Walraven colours, due primarily to surface gravity effects.
Massive soliton stars
Chiu, Hong-Yee
The structure of nontopological solutions of Einstein field equations as proposed by Friedberg, Lee, and Pang (1987) is examined. This analysis incorporates finite temperature effects and pair creation. Quarks are assumed to be the only species that exist in interior of soliton stars. The possibility of primordial creation of soliton stars in the incomplete decay of the degenerate vacuum in early universe is explored. Because of dominance of pair creation inside soliton stars, the luminosity of soliton stars is not determined by its radiative transfer characteristics, and the surface temperature of soliton stars can be the same as its interior temperature. It is possible that soliton stars are intense X-ray radiators at large distances. Soliton stars are nearly 100 percent efficient energy converters, converting the rest energy of baryons entering the interior into radiation. It is possible that a sizable number of baryons may also be trapped inside soliton stars during early epochs of the universe. In addition, if soliton stars exist they could assume the role played by massive black holes in galactic centers.
The sun, moon and stars of the southern Levant at Gezer and Megiddo: Cultural astronomy in Chalcolithic/Early and Middle Bronze Ages
Gardner, Sara Lee
Astronomical images are found on monumental structures and decorative art, and metaphorically in seasonal myths, and are documented by calendars. In Israel and the southern Levant, images of the sun, the moon, and the stars were common decorating motifs. They were found on walls, pottery, and seals and date to as early as the Chalcolithic period; for example, the wall painting of a star at Teleilat Ghassul (North 1961). This dissertation establishes that the people of the Levant were aware of the apparent movement of the sun, and this will be discussed in Chapter 4. They began recording through representation drawings, astronomical phenomena no later than the Chalcolithic/Early Bronze Age and continued to do so late into the Middle Bronze Age. The argument moves beyond the simple use of symbols to the use of images to represent constellations, with the focus on the constellation Leo in Chapter 5. Furthermore, the use of astronomy as a power and political tool is also suggested in Chapter 6. Nonetheless, the primary purpose that is addressed here is the tendency in Syro-Palestinian archaeology has been to attribute technological evidence found in the northern and southern Levant as diffused from Egypt or Assyria, particularly astronomy. This dissertation firmly establishes that astronomy was used in the southern Levant before any significant contact with the civilizations of Egypt or Assyria.
The low-metallicity starburst NGC346: massive-star population and feedback
Oskinova, Lida
The Small Magellanic Cloud (SMC) is ideal to study young, massive stars at low metallicity. The compact cluster NGC346 contains about half of all O-type stars in the entire SMC. The massive-star population of this cluster powers N66, the brightest and largest HII region in the SMC. We propose to use HST-STIS to slice NGC346 with 20 long-slit exposures, in order to obtain the UV spectra of most of the massive early-type stars of this cluster. Archival data of 13 exposures that cover already a minor part of this cluster will be included in our analyses. Our aim is to quantitatively analyze virtually the whole massive-star population of NGC346. We have already secured the optical spectra of all massive stars in the field with the integral-field spectrograph MUSE at the ESO-VLT. However, for the determination of the stellar-wind parameters, i.e. the mass-loss rates and the wind velocities, ultraviolet spectra are indispensable. Our advanced Potsdam Wolf-Rayet (PoWR) code will be used for modeling the stellar and wind spectra in the course of the analysis. Finally, we will obtain:(a) the fundamental stellar and wind parameters of all stars brighter than spectral type B2V in the field, which, e,g,, will constrain the initial mass function in this young low-metallicity starburst;(b) mass-loss rates of many more OB-type stars at SMC metallicity than hitherto known, allowing to better constrain their metallicity dependence;(c) the integrated feedback by ionizing radiation and stellar winds of the whole massive-star population of NGC346, which will be used as input to model the ecology of the giant HII region N66.These HST UV data will be of high legacy value.
Interpretation of the BRITE oscillation spectra of the early B-type stars: ν Eri and α Lupi
Walczak, P.; Daszyńska-Daszkiewicz, J.; Pamyatnykh, A.; Handler, G.; Pigulski, A.
ν Eridani is a well known multiperiodic β Cephei pulsator which exhibits also the SPB (Slowly Pulsating B-type stars) type modes. Recent frequency analysis of the BRITE photometry of α Lupi showed that the star is also a hybrid β Cep/SPB pulsator, in which both high and low frequencies were detected. We construct complex seismic models in order to account for the observed frequency range, the values of the frequencies themselves and the non-adiabatic parameter f for the dominant mode. Our studies suggest that significant modifications of the opacity profile at the temperature range log{T}\\in (5.0-5.5) are necessary to fulfill all these requirements.
A Reconnaissance of the 900-1200 A Spectra of Early O Stars in the Magellanic Clouds
Walborn, Nolan
Far-UV spectrograms of ten very hot stars in the Magellanic Clouds were obtained with the Hopkins Ultraviolet Telescope during the Astro-2 mission in March 1995. Very few normal OB stars were observed during Astro-1, and the only significant prior sample of such objects in this wavelength range was that obtained by Copernicus of stars near the Sun. The Magellanic Cloud sample offers the advantages of low reddening, a range in metallicity, and more extreme temperatures and luminosities than represented in the near solar neighborhood. Several interesting phenomena were found in the HUT MC sample, including very strong O VI wind profiles in O3 spectra; anomalous CNO wind features corresponding to abundances altered by stellar nucleosynthesis; weak wind features due to the metal deficiency of the Small Magellanic Cloud; and interstellar molecular hydrogen features originating in the MCs. The results were presented and discussed as a small atlas, and they were shown at the Pittsburgh AAS meeting in June 1995. A correlative atlas of Copernicus data was also prepared and published under the auspices of this grant. These publications will serve as resources for the characterization of the FUSE observations of related objects to hopefully be obtained soon. I believe that the large differences among the strong wind features in the HUT data, corresponding to CNO and systemic metallicity effects, are amenable to some relative quantitative analysis, and I shall endeavor to promote such in conjunction with HST data at longer wavelengths for the same stars (which has also not yet been completely analyzed) at a future opportunity.
Elemental abundance analyses with DAO spectrograms: XXX. The middle B through early A stars ξ2 Ceti (B9 III), 21 Aquilae (B8 II-III), ι Aquilae (B5 III), and ι Delphini (A2V)
Adelman, S. J.; Westbrook, P. C.; Gulliver, A. F.
This series of high quality elemental abundance analyses of mostly main-sequence band normal and peculiar B, A, and F stars defines their properties and provides data for the comparison with the analyses of somewhat similar stars and with theoretical predictions. Most use high dispersion and high S/N (≥ 200) spectrograms obtained with CCD detectors at the long camera of the Coudé spectrograph of the 1.22-m Dominion Astrophysical Observatory telescope. Here we reanalyze 21 Aql with better quality spectra and increase the number of stars consistently analyzed in the spectral range B5 to A2 by analyzing three new stars for this series. In the early A stars the normal and non-mCP stars have abundances with overlapping ranges. But more stars are needed especially in the B5 to B9 range. ξ2 Cet on average has a solar composition with a few abundances outside the solar range while both 21 Aql and ι Aql have abundances marginally less than solar. The abundances of ι Del are greater than solar with a few elements such as Ca being less than solar. It is an Am star. Table 3 is only available in electronic form at the CDS via http://cdsarc.u-strasbg.fr/ftp/cats/J/other/AN/331/378
Inferring the star-formation histories of the most massive and passive early-type galaxies at z < 0.3
Citro, Annalisa; Pozzetti, Lucia; Moresco, Michele; Cimatti, Andrea
Context. In the Λ cold dark matter (ΛCDM) cosmological framework, massive galaxies are the end-points of the hierarchical evolution and are therefore key probes for understanding how the baryonic matter evolves within the dark matter halos. Aims: The aim of this work is to use the archaeological approach in order to infer the stellar population properties and star formation histories of the most massive (M > 1010.75 M⊙) and passive early-type galaxies (ETGs) at 0 < z < 0.3 (corresponding to a cosmic time interval of ~3.3 Gyr) based on stacked, high signal-to-noise (S/N), spectra extracted from the Sloan Digital Sky Survey (SDSS). Our study is focused on the most passive ETGs in order to avoid the contamination of galaxies with residual star formation activity and extract the evolutionary information on the oldest envelope of the global galaxy population. Methods: Unlike most previous studies in this field, we did not rely on individual absorption features such as the Lick indices, but we used the information present in the full spectrum with the STARLIGHT public code, adopting different stellar population synthesis models. Successful tests have been performed to assess the reliability of STARLIGHT to retrieve the evolutionary properties of the ETG stellar populations such as the age, metallicity and star formation history. The results indicate that these properties can be derived with accuracy better than 10% at S/N ≳ 10-20, and also that the procedure of stacking galaxy spectra does not introduce significant biases into their retrieval. Results: Based on our spectral analysis, we found that the ETGs of our sample are very old systems - the most massive ones are almost as old as the Universe. The stellar metallicities are slightly supersolar, with a mean of Z ~ 0.027 ± 0.002 and Z ~ 0.029 ± 0.0015 (depending on the spectral synthesis models used for the fit) and do not depend on redshift. Dust extinction is very low, with a mean of AV ~ 0.08 ± 0.030 mag
KELT-20b: A Giant Planet with a Period of P ˜ 3.5 days Transiting the V ˜ 7.6 Early A Star HD 185603
Lund, Michael B.; Rodriguez, Joseph E.; Zhou, George; Gaudi, B. Scott; Stassun, Keivan G.; Johnson, Marshall C.; Bieryla, Allyson; Oelkers, Ryan J.; Stevens, Daniel J.; Collins, Karen A.; Penev, Kaloyan; Quinn, Samuel N.; Latham, David W.; Villanueva, Steven, Jr.; Eastman, Jason D.; Kielkopf, John F.; Oberst, Thomas E.; Jensen, Eric L. N.; Cohen, David H.; Joner, Michael D.; Stephens, Denise C.; Relles, Howard; Corfini, Giorgio; Gregorio, Joao; Zambelli, Roberto; Esquerdo, Gilbert A.; Calkins, Michael L.; Berlind, Perry; Ciardi, David R.; Dressing, Courtney; Patel, Rahul; Gagnon, Patrick; Gonzales, Erica; Beatty, Thomas G.; Siverd, Robert J.; Labadie-Bartz, Jonathan; Kuhn, Rudolf B.; Colón, Knicole D.; James, David; Pepper, Joshua; Fulton, Benjamin J.; McLeod, Kim K.; Stockdale, Christopher; Calchi Novati, Sebastiano; DePoy, D. L.; Gould, Andrew; Marshall, Jennifer L.; Trueblood, Mark; Trueblood, Patricia; Johnson, John A.; Wright, Jason; McCrady, Nate; Wittenmyer, Robert A.; Johnson, Samson A.; Sergi, Anthony; Wilson, Maurice; Sliski, David H.
We report the discovery of KELT-20b, a hot Jupiter transiting a V˜ 7.6 early A star, HD 185603, with an orbital period of P≃ 3.47 days. Archival and follow-up photometry, Gaia parallax, radial velocities, Doppler tomography, and AO imaging were used to confirm the planetary nature of KELT-20b and characterize the system. From global modeling we infer that KELT-20 is a rapidly rotating (v\\sin {I}* ≃ 120 {km} {{{s}}}-1) A2V star with an effective temperature of {T}{eff}={8730}-260+250 K, mass of {M}* ={1.76}-0.20+0.14 {M}⊙ , radius of {R}* ={1.561}-0.064+0.058 {R}⊙ , surface gravity of {log}{g}* ={4.292}-0.020+0.017, and age of ≲ 600 {Myr}. The planetary companion has a radius of {R}P={1.735}-0.075+0.070 {R}{{J}}, a semimajor axis of a={0.0542}-0.0021+0.0014 au, and a linear ephemeris of {{BJD}}{TDB}=2457503.120049+/- 0.000190 +E(3.4741070+/- 0.0000019). We place a 3σ upper limit of ˜ 3.5 {M}{{J}} on the mass of the planet. Doppler tomographic measurements indicate that the planetary orbit normal is well aligned with the projected spin axis of the star (λ =3\\buildrel{\\circ}\\over{.} 4+/- 2\\buildrel{\\circ}\\over{.} 1). The inclination of the star is constrained to 24\\buildrel{\\circ}\\over{.} 4< {I}* < 155\\buildrel{\\circ}\\over{.} 6, implying a three-dimensional spin-orbit alignment of 1\\buildrel{\\circ}\\over{.} 3< \\psi < 69\\buildrel{\\circ}\\over{.} 8. KELT-20b receives an insolation flux of ˜ 8× {10}9 {erg} {{{s}}}-1 {{cm}}-2, implying an equilibrium temperature of of ˜2250 K, assuming zero albedo and complete heat redistribution. Due to the high stellar {T}{eff}, KELT-20b also receives an ultraviolet (wavelength d≤slant 91.2 nm) insolation flux of ˜ 9.1× {10}4 {erg} {{{s}}}-1 {{cm}}-2, possibly indicating significant atmospheric ablation. Together with WASP-33, Kepler-13 A, HAT-P-57, KELT-17, and KELT-9, KELT-20 is the sixth A star host of a transiting giant planet, and the third-brightest host (in V) of a transiting planet.
Quantitative UV spectroscopy of early O stars on the Magellanic Clouds: The determination of the stellar metallicities
Haser, Stefan M.; Pauldrach, Adalbert W. A.; Lennon, Danny J.; Kudritzki, Rolf-Peter; Lennon, Maguerite; Puls, Joachim; Voels, Stephen A.
Ultraviolet spectra of four O stars in the Magellanic Clouds obtained with the faint object spectrograph of the Hubble Space Telescope are analyzed with respect to their metallicity. The metal abundances are derived from the stellar parameters and the mass loss rate with a two step procedure: hydrodynamic radiation-driven wind models with metallicity as a free parameter are constructed to fit the observed wind momentum rate and thus yield a dynamical metallicity, and synthetic spectra are computed for different metal abundances and compared to the observed spectra in order to obtain a spectroscopic metallicity.
Present-day cosmic abundances. A comprehensive study of nearby early B-type stars and implications for stellar and Galactic evolution and interstellar dust models
Nieva, M.-F.; Przybilla, N.
Context. Early B-type stars are ideal indicators for present-day cosmic abundances since they preserve their pristine abundances and typically do not migrate far beyond their birth environments over their short lifetimes, in contrast to older stars like the Sun. They are also unaffected by depletion onto dust grains, unlike the cold/warm interstellar medium (ISM) or H ii regions. Aims: A carefully selected sample of early B-type stars in OB associations and the field within the solar neighbourhood is studied comprehensively. Quantitative spectroscopy is used to characterise their atmospheric properties in a self-consistent way. Present-day abundances for the astrophysically most interesting chemical elements are derived in order to investigate whether a present-day cosmic abundance standard can be established. Methods: High-resolution and high-S/N FOCES, FEROS and ELODIE spectra of well-studied sharp-lined early B-type stars are analysed in non-LTE. Line-profile fits based on extensive model grids and an iterative analysis methodology are used to constrain stellar parameters and elemental abundances at high accuracy and precision. Atmospheric parameters are derived from the simultaneous establishment of independent indicators, from multiple ionization equilibria and the Stark-broadened hydrogen Balmer lines, and they are confirmed by reproduction of the stars' global spectral energy distributions. Results: Effective temperatures are constrained to 1-2% and surface gravities to less than 15% uncertainty, along with accurate rotational, micro- and macroturbulence velocities. Good agreement of the resulting spectroscopic parallaxes with those from the new reduction of the Hipparcos catalogue is obtained. Absolute values for abundances of He, C, N, O, Ne, Mg, Si and Fe are determined to better than 25% uncertainty. The synthetic spectra match the observations reliably over almost the entire visual spectral range. Three sample stars, γ Ori, o Per and θ1 Ori D, are
X1908+075: A Late O-Type Supergiant with a Neutron Star Companion
Morel, Thierry; Grosdidier, Yves
X1908 + 075 is a highly-absorbed Galactic X-ray source likely made up of a pulsar accreting wind material from a massive companion. We have used near-IR photometric data complemented by follow-up spectroscopy to identify the likely counterpart to this X-ray source and to assign a spectral type O7.5 9.5 If to the primary. Further details can be found in Morel and Grosdidier (2005).
Lessons from the Lone Star State: Designing a Sustainable Financial Model to Expand Early College High School in Texas
Goldberger, Susan; Santos, Janet
Texas is a national leader in creating early college high schools, an innovative small school model that blends secondary and postsecondary education with intensive supports to increase college readiness and success for underachieving students. The state has 29 early college schools, with more opening in the 2008-2009 academic year, thanks largely…
Sizing up the stars
Boyajian, Tabetha S.
For the main part of this dissertation, I have executed a survey of nearby, main sequence A, F, and G-type stars with the CHARA Array, successfully measuring the angular diameters of forty-four stars to better than 4% accuracy. The results of these observations also yield empirical determinations of stellar linear radii and effective temperatures for the stars observed. In addition, these CHARA-determined temperatures, radii, and luminosities are fit to Yonsei-Yale isochrones to constrain the masses and ages of the stars. These quantities are compared to the results found in Allende Prieto & Lambert (1999), Holmberg et al. (2007), and Takeda (2007), who indirectly determine these same properties by fitting models to observed photometry. I find that for most cases, the models underestimate the radius of the star by ~ 12%, while in turn they overestimate the effective temperature by ~ 1.5-4%, when compared to my directly measured values, with no apparent correlation to the star's metallicity or color index. These overestimated temperatures and underestimated radii in these works appear to cause an additional offset in the star's surface gravity measurements, which consequently yield higher masses and younger ages, in particular for stars with masses greater than ~ 1.3 [Special characters omitted.] . Alternatively, these quantities I measure are also compared to direct measurements from a large sample of eclipsing binary stars in Andersen (1991), and excellent agreement is seen within both data sets. Finally, a multi-parameter solution is found to fit color-temperature-metallicity values of the stars in this sample to provide a new calibration of the effective temperature scale for these types of stars. Published work in the field of stellar interferometry and optical spectroscopy of early-type stars are presented in Appendix D and E, respectively. INDEX WORDS: Interferometry, Infrared, Stellar Astronomy, Fundamental Properties, Effective Temperatures, Stellar Radii
Strange stars
Alcock, Charles; Farhi, Edward; Olinto, Angela
Strange matter, a form of quark matter that is postulated to be absolute stable, may be the true ground stage of the hadrons. If this hypothesis is correct, neutron stars may convert to 'strange stars'. The mass-radius relation for strange stars is very different from that of neutron stars; there is no minimum mass, and for mass of 1 solar mass or less, mass is proportional to the cube of the radius. For masses between 1 solar mass and 2 solar masses, the radii of strange stars are about 10 km, as for neutron stars. Strange stars may have an exposed quark surface, which is capable of radiating at rates greatly exceeding the Eddington limit, but has a low emissivity for X-ray photons. The stars may have a thin crust with the same composition as the preneutron drip outer layer of a conventional neutron star crust. Strange stars cool efficiently via neutrino emission.
Stars and Star Myths.
Eason, Oliver
Myths and tales from around the world about constellations and facts about stars in the constellations are presented. Most of the stories are from Greek and Roman mythology; however, a few Chinese, Japanese, Polynesian, Arabian, Jewish, and American Indian tales are also included. Following an introduction, myths are presented for the following 32…
New CCD photometric investigation of the early-type overcontact binary BH Cen in the young star-forming Galactic cluster IC 2944
Zhao, Er-Gang; Qian, Sheng-Bang; Zejda, Miloslav; Zhang, Bin; Zhang, Jia
BH Cen is a short-period early-type binary with a period of 0.792d in the extremely young star-forming cluster IC 2944. New multi-color CCD photometric light curves in U, B, V, R and I bands are presented and are analyzed by using the Wilson-Devinney code. It is detected that BH Cen is a high-mass-ratio overcontact binary with a fill-out factor of 46.4% and a mass ratio of 0.89. The derived orbital inclination i is 88.9 degrees, indicating that it is a totally eclipsing binary and the photometric parameters can be determined reliably. By adding new eclipse times, the orbital period changes in the binary are analyzed. It is confirmed that the period of BH Cen shows a long-term increase while it undergoes a cyclic oscillation with an amplitude of A 3 = 0.024 d and a period of P 3 = 50.3 yr. The high mass ratio, overcontact configuration and long-term continuous increase in the orbital period all suggest that BH Cen is in the evolutionary state after the shortest-period stage of Case A mass transfer. The continuous increase in period can be explained by mass transfer from the secondary component to the primary one at a rate of Ṁ 2 = 2.8 × 10‑6 M ⊙ per year. The cyclic change can be plausibly explained by the presence of a third body because both components in the BH Cen system are early-type stars. Its mass is determined to be no less than 2.2 M ⊙ at an orbital separation of about 32.5 AU. Since no third light was found during the photometric solution, it is possible that the third body may be a candidate for a compact object.
WEAK AND COMPACT RADIO EMISSION IN EARLY HIGH-MASS STAR-FORMING REGIONS. I. VLA OBSERVATIONS
Rosero, V.; Hofner, P.; Claussen, M.
We present a high-sensitivity radio continuum survey at 6 and 1.3 cm using the Karl G. Jansky Very Large Array toward a sample of 58 high-mass star-forming regions. Our sample was chosen from dust clumps within infrared dark clouds with and without IR sources (CMC–IRs and CMCs, respectively), and hot molecular cores (HMCs), with no previous, or relatively weak radio continuum detection at the 1 mJy level. Due to the improvement in the continuum sensitivity of the Very Large Array, this survey achieved map rms levels of ∼3–10 μ Jy beam{sup −1} at sub-arcsecond angular resolution. We extracted 70 continuum sourcesmore » associated with 1.2 mm dust clumps. Most sources are weak, compact, and prime candidates for high-mass protostars. Detection rates of radio sources associated with the millimeter dust clumps for CMCs, CMC–IRs, and HMCs are 6%, 53%, and 100%, respectively. This result is consistent with increasing high-mass star formation activity from CMCs to HMCs. The radio sources located within HMCs and CMC–IRs occur close to the dust clump centers, with a median offset from it of 12,000 au and 4000 au, respectively. We calculated 5–25 GHz spectral indices using power-law fits and obtained a median value of 0.5 (i.e., flux increasing with frequency), suggestive of thermal emission from ionized jets. In this paper we describe the sample, observations, and detections. The analysis and discussion will be presented in Paper II.« less
Pulsating Stars
Catelan, M.; Smith, H. A.
This book surveys our understanding of stars which change in brightness because they pulsate. Pulsating variable stars are keys to distance scales inside and beyond the Milky Way galaxy. They test our understanding not only of stellar pulsation theory but also of stellar structure and evolution theory. Moreover, pulsating stars are important probes of the formation and evolution of our own and neighboring galaxies. Our understanding of pulsating stars has greatly increased in recent years as large-scale surveys of pulsating stars in the Milky Way and other Local Group galaxies have provided a wealth of new observations and as space-based instruments have studied particular pulsating stars in unprecedented detail.
The Magnetic Properties of Galactic OB Stars from the Magnetism in Massive Stars Project
Wade, Gregg A.; Grunhut, Jason; Petit, Veronique; Neiner, Coralie; Alecian, Evelyne; Landstreet, John; MiMeS Collaboration
The Magnetism in Massive Stars (MiMeS) project represents the largest systematic survey of stellar magnetism ever undertaken. Comprising nearly 4500 high resolution polarised spectra of nearly 550 Galactic B and O-type stars, the MiMeS survey aims to address interesting and fundamental questions about the magnetism of hot, massive stars: How and when are massive star magnetic fields generated, and how do they evolve throughout stellar evolution? How do magnetic fields couple to and interact with the powerful winds of OB stars, and what are the consequences for the wind structure, momentum flux and energetics? What are the detailed physical mechanisms that lead to the anomalously slow rotation of many magnetic massive stars? What is the ultimate impact of stellar magnetic fields -- both direct and indirect -- on the evolution of massive stars? In this talk we report results from the analysis of the B-type stars observed within the MiMeS survey. The sample consists of over 450 stars ranging in spectral type from B9 to B0, and in evolutionary stage from the pre-main sequence to the post-main sequence. In addition to general statistical results concerning field incidence, strength and topology, we will elaborate our conclusions for subsamples of special interest, including the Herbig and classical Be stars, pulsating B stars and chemically peculiar B stars.
Rosettes, Engrailed Edges, and Star-Shaped Patterns: Between Rediscovery and Forgetfulness in the Early Accounts of Vibrating Liquid Drops Floating over Hot Surfaces.
Stewart, Seán M
Small drops of liquid brought into contact with very hot surfaces float above it as beautiful, slightly flattened spheroids without coming to the boil. An example of film boiling, drops that are sessile can often suddenly and quite unexpectedly start to oscillate forming highly symmetric patterns of surprising pulchritude. The rim of these oscillating drops take on "star-shaped" patterns with many different modes of vibration possible. Still an object of study today, their discovery, early accounts, rediscovery and ensuing controversies over claims of priority, before quietly slipping away from the collective memory of the scientific community to become all but forgotten makes for a compelling story in the early history of film boiling. The episode serves not only as a valuable reminder of the importance the history of science can play in highlighting past achievements that would otherwise remain unknown to the modern practitioner. It also provides an example of how external pressures and personal ambition can often influence the work of a scientist in their pursuit of self-recognition and acclaim amongst their peers. Copyright © 2017 Elsevier Ltd. All rights reserved.
Massive stars, disks, and clustered star formation
Moeckel, Nickolas Barry
The formation of an isolated massive star is inherently more complex than the relatively well-understood collapse of an isolated, low-mass star. The dense, clustered environment where massive stars are predominantly found further complicates the picture, and suggests that interactions with other stars may play an important role in the early life of these objects. In this thesis we present the results of numerical hydrodynamic experiments investigating interactions between a massive protostar and its lower-mass cluster siblings. We explore the impact of these interactions on the orientation of disks and outflows, which are potentially observable indications of encounters during the formation of a star. We show that these encounters efficiently form eccentric binary systems, and in clusters similar to Orion they occur frequently enough to contribute to the high multiplicity of massive stars. We suggest that the massive protostar in Cepheus A is currently undergoing a series of interactions, and present simulations tailored to that system. We also apply the numerical techniques used in the massive star investigations to a much lower-mass regime, the formation of planetary systems around Solar- mass stars. We perform a small number of illustrative planet-planet scattering experiments, which have been used to explain the eccentricity distribution of extrasolar planets. We add the complication of a remnant gas disk, and show that this feature has the potential to stabilize the system against strong encounters between planets. We present preliminary simulations of Bondi-Hoyle accretion onto a protoplanetary disk, and consider the impact of the flow on the disk properties as well as the impact of the disk on the accretion flow.
Testing the Wind-shock Paradigm for B-Type Star X-Ray Production with θ Car
Doyle, T. F.; Petit, V.; Cohen, D.; Leutenegger, M.
We present Chandra X-ray grating spectroscopy of the B0.2V star, θ Carina. θ Car is in a critical transition region between the latest O-type and earliest B-type stars, where some stars are observed to have UV-determined wind densities much lower than theoretically expected (e.g., Marcolino et al. 2009). In general, X-ray emission in this low-density wind regime should be less prominent than for O-stars (e.g., Martins et al. 2005), but observations suggest a higher than expected X-ray emission filling factor (Lucy 2012; Huenemoerder et al. 2012); if a larger fraction of the wind is shock-heated, it could explain the weak UV wind signature seen in weak wind stars, but this might severely challenge predictions of radiatively-driven wind theory. We measured the line widths of several He-, H-like and Fe ions and the f/i ratio of He-like ions in the X-ray spectrum, which improves upon the results from Nazé et al. (2008) (XMM-Newton RGS) with additional measurements (Chandra HETG) of Mgxi and Sixiii by further constraining the X-ray emission location. The f/i ratio is modified by the proximity to the UV-emitting stellar photosphere, and is therefore a diagnostic of the radial location of the X-ray emitting plasma. The measured widths of X-ray lines are narrow, <300 km s-1 and the f/i ratios place the X-rays relatively close to the surface, both implying θ Car is a weak wind star. The measured widths are also consistent with other later-type stars in the weak wind regime, β Cru (Cohen et al. 2008), for example, and are smaller on average than earlier weak wind stars such as μ Col (Huenemoerder et al. 2012). This could point to a spectral type divide, where one hypothesis, low density, works for early-B type stars and the other hypothesis, a larger fraction of shock-heated gas, explains weak winds in late-O type stars. Archival IUE data still needs to be analyzed to determine the mass loss rate and hydrodynamical simulations will be compared with observations to
MASSIVE STARS IN THE LOCAL GROUP: Implications for Stellar Evolution and Star Formation
Massey, Philip
The galaxies of the Local Group serve as important laboratories for understanding the physics of massive stars. Here I discuss what is involved in identifying various kinds of massive stars in nearby galaxies: the hydrogen-burning O-type stars and their evolved He-burning evolutionary descendants, the luminous blue variables, red supergiants, and Wolf-Rayet stars. Primarily I review what our knowledge of the massive star population in nearby galaxies has taught us about stellar evolution and star formation. I show that the current generation of stellar evolutionary models do well at matching some of the observed features and provide a look at the sort of new observational data that will provide a benchmark against which new models can be evaluated.
The APOGEE-2 Survey of the Orion Star-forming Complex. I. Target Selection and Validation with Early Observations
Cottle, J.'Neil; Covey, Kevin R.; Suárez, Genaro; Román-Zúñiga, Carlos; Schlafly, Edward; Downes, Juan Jose; Ybarra, Jason E.; Hernandez, Jesus; Stassun, Keivan; Stringfellow, Guy S.; Getman, Konstantin; Feigelson, Eric; Borissova, Jura; Kim, J. Serena; Roman-Lopes, A.; Da Rio, Nicola; De Lee, Nathan; Frinchaboy, Peter M.; Kounkel, Marina; Majewski, Steven R.; Mennickent, Ronald E.; Nidever, David L.; Nitschelm, Christian; Pan, Kaike; Shetrone, Matthew; Zasowski, Gail; Chambers, Ken; Magnier, Eugene; Valenti, Jeff
The Orion Star-forming Complex (OSFC) is a central target for the APOGEE-2 Young Cluster Survey. Existing membership catalogs span limited portions of the OSFC, reflecting the difficulty of selecting targets homogeneously across this extended, highly structured region. We have used data from wide-field photometric surveys to produce a less biased parent sample of young stellar objects (YSOs) with infrared (IR) excesses indicative of warm circumstellar material or photometric variability at optical wavelengths across the full 420 square degree extent of the OSFC. When restricted to YSO candidates with H < 12.4, to ensure S/N ∼ 100 for a six-visit source, this uniformly selected sample includes 1307 IR excess sources selected using criteria vetted by Koenig & Liesawitz (2014) and 990 optical variables identified in the Pan-STARRS1 3π survey: 319 sources exhibit both optical variability and evidence of circumstellar disks through IR excess. Objects from this uniformly selected sample received the highest priority for targeting, but required fewer than half of the fibers on each APOGEE-2 plate. We filled the remaining fibers with previously confirmed and new color–magnitude selected candidate OSFC members. Radial velocity measurements from APOGEE-1 and new APOGEE-2 observations taken in the survey's first year indicate that ∼90% of the uniformly selected targets have radial velocities consistent with Orion membership. The APOGEE-2 Orion survey will include >1100 bona fide YSOs whose uniform selection function will provide a robust sample for comparative analyses of the stellar populations and properties across all sub-regions of Orion.
Massive Stars
Livio, Mario; Villaver, Eva
Participants; Preface Mario Livio and Eva Villaver; 1. High-mass star formation by gravitational collapse of massive cores M. R. Krumholz; 2. Observations of massive star formation N. A. Patel; 3. Massive star formation in the Galactic center D. F. Figer; 4. An X-ray tour of massive star-forming regions with Chandra L. K. Townsley; 5. Massive stars: feedback effects in the local universe M. S. Oey and C. J. Clarke; 6. The initial mass function in clusters B. G. Elmegreen; 7. Massive stars and star clusters in the Antennae galaxies B. C. Whitmore; 8. On the binarity of Eta Carinae T. R. Gull; 9. Parameters and winds of hot massive stars R. P. Kudritzki and M. A. Urbaneja; 10. Unraveling the Galaxy to find the first stars J. Tumlinson; 11. Optically observable zero-age main-sequence O stars N. R. Walborn; 12. Metallicity-dependent Wolf-Raynet winds P. A. Crowther; 13. Eruptive mass loss in very massive stars and Population III stars N. Smith; 14. From progenitor to afterlife R. A. Chevalier; 15. Pair-production supernovae: theory and observation E. Scannapieco; 16. Cosmic infrared background and Population III: an overview A. Kashlinsky.
ALMA Observations of N83C in the Early Stage of Star Formation in the Small Magellanic Cloud
Muraoka, Kazuyuki; Homma, Aya; Onishi, Toshikazu; Tokuda, Kazuki; Harada, Ryohei; Morioka, Yuuki; Zahorecz, Sarolta; Saigo, Kazuya; Kawamura, Akiko; Mizuno, Norikazu; Minamidani, Tetsuhiro; Muller, Erik; Fukui, Yasuo; Meixner, Margaret; Indebetouw, Remy; Sewiło, Marta; Bolatto, Alberto
We have performed Atacama Large Millimeter/submillimeter Array (ALMA) observations in the 12CO(J=2-1), 13CO(J=2-1), C18O(J=2-1), 12CO(J=3-2), 13CO(J=3-2), and CS(J=7-6) lines toward the active star-forming region N83C in the Small Magellanic Cloud (SMC), whose metallicity is about one-fifth of the Milky Way (MW). The ALMA observations first reveal subparsec-scale molecular structures in 12CO(J=2-1) and 13CO(J=2-1) emissions. We found strong CO peaks associated with young stellar objects (YSOs) identified by the Spitzer Space Telescope, and we also found that overall molecular gas is distributed along the edge of the neighboring {{H}} II region. We derived a gas density of ˜ {10}4 cm-3 in molecular clouds associated with YSOs based on the virial mass estimated from the 12CO(J=2-1) emission. This high gas density is presumably due to the effect of the {{H}} II region under the low-metallicity (and accordingly small-dust content) environment in the SMC; far-UV radiation from the {{H}} II region can easily penetrate and photodissociate the outer layer of 12CO molecules in the molecular clouds, and thus only the innermost parts of the molecular clouds are observed even in 12CO emission. We obtained the CO-to-H2 conversion factor {X}{CO} of 7.5× {10}20 cm-2 (K km s-1)-1 in N83C based on virial masses and CO luminosities, and it is four times larger than that in the MW, 2 × {10}20 cm-2 (K km s-1)-1. We also discuss the difference in the nature between two high-mass YSOs, each of which is associated with a molecular clump with a mass of about a few × {10}3 {M}⊙ .
The Evolution of Carbon Stars
Chan, S. Josephine
-type stars (^13C-rich carbon stars) have been suggested to be transition objects between M-type stars and C-type stars. An optical spectroscopic study of these silicate carbon stars was performed at the Dominion Astrophysical Observatory (DAO) in Victoria in 1991. CCGCS 1653, CCGCS 4222, CCGCS 4923 and CCGCS 5848 have been confirmed to be J stars. CCGCS 1158 and CCGCS 4729 are provisionally identified as J stars. A preliminary spectral analysis has also been carried out. Model calculations are presented on the evolution from the visual carbon stars to infrared carbon stars, and on the evolution of infrared carbon stars. A new empirical opacity function for the SiC grain is derived based on the LRS spectra of a selected sample of infrared carbon stars. A two-shell model has been developed with an oxygen-rich detached shell and a newly-forming SiC dust shell. The energy distributions of ~110 transition objects which are late-stage visual carbon stars or early-stage infrared carbon stars are fitted with this Interrupted Mass Loss Model. Furthermore, the model tracks successfully explain the "C" shaped distribution of the transition objects in the IRAS 12 microns/25 microns/60 microns colour-colour diagram. The energy distributions of ~150 infrared carbon stars are also matched with a radiative transfer dust shell model using only SiC dust. The colour evolution of infrared carbon stars can be explained with a continuous increase in mass loss rate on the AGB. An evolutionary scenario of AGB stars is suggested. There is a branching of M-type and C-type stars on the AGB with each branch evolving independently to the planetary nebula stage. The initial mass of the star in the main sequence may be the factor that determines which branch the star will follow. (SECTION: Dissertation Abstracts)
[CII] At 1 < z < 2: Observing Star Formation in the Early Universe with Zeus (1 and 2)
Ferkinhoff, Carl; Hailey-Dunsheath, S.; Nikola, T.; Oberst, T.; Parshley, S.; Stacey, G.; Benford, D.; staguhn, J.
We report the detection of the [CII] 158 micron fine structure line from six submillimeter galaxies with redshifts between 1.12 and 1.73. This more than doubles the total number of [CII] 158 micron detections reported from high redshift sources. These observations were made with the Redshift(z) and Early Universe Spectrometer(ZEUS) at the Caltech Submillimeter Observatory on Mauna Kea, Hawaii between December 2006 and March 2009. ZEUS is a background limited submm echelle grating spectrometer (Hailey-Dunsheath 2009). Currently we are constructing ZEUS-2. This new instrument will utilize the same grating but will feature a two dimensional transition-edge sensed bolometer array with SQUID multiplexing readout system enabling simultaneous background limited observations in the 200, 340,450 and 650 micron telluric windows. ZEUS-2 will allow for long slit imaging spectroscopy in nearby galaxies and a [CII] survey from z 0.25 to 2.5.
Colliding Winds and Tomography of O-Type Binaries
Gies, Dougles R.
This grant was awarded in support of an observational study with the NASA IUE Observatory during the 15th episode (1992), and it subsequently also supported our continuing work in 16th (1994) and 18th (1995) episodes. The project involved the study of FUV spectra of massive spectroscopic binary systems containing hot stars of spectral type O. We applied a Doppler tomography algorithm to reconstruct the individual component UV spectra of stars in order to obtain improved estimates of the temperature, gravity, UV intensity ratio, and projected rotational velocity for stars in each system, and to make a preliminary survey for abundance anomalies through comparison with standard spectra. We also investigated the orbital phase-related variations in the UV stellar wind lines to probe the geometries of wind-wind collisions in these systems. The project directly supported two Ph.D. dissertations at Georgia State University (by Penny and Thaller), and we are grateful for this support. No inventions were made in the performance of this work. Detailed results are summarized in the abstracts listed in the following section.
Young Star Clusters: Keys to Understanding Massive Stars
Davies, B.
Young, coeval clusters of stars provide the perfect laboratory in which to test our understanding of how massive stars evolve. Early optical observations limited us to a handful of low-mass clusters within 1kpc. However, thanks to the recent progress in infrared astronomy, the Milky Way's population of young massive star clusters is now beginning to be revealed. Here, I will review the recent progress made in this field, what it has told us about the evolution of massive stars to supernova and beyond, the prospects for this field, and some issues that should be taken into account when interpreting the results.
Impacts of ocean acidification on early life-history stages and settlement of the coral-eating sea star Acanthaster planci.
Uthicke, Sven; Pecorino, Danilo; Albright, Rebecca; Negri, Andrew Peter; Cantin, Neal; Liddy, Michelle; Dworjanyn, Symon; Kamya, Pamela; Byrne, Maria; Lamare, Miles
Coral reefs are marine biodiversity hotspots, but their existence is threatened by global change and local pressures such as land-runoff and overfishing. Population explosions of coral-eating crown of thorns sea stars (COTS) are a major contributor to recent decline in coral cover on the Great Barrier Reef. Here, we investigate how projected near-future ocean acidification (OA) conditions can affect early life history stages of COTS, by investigating important milestones including sperm motility, fertilisation rates, and larval development and settlement. OA (increased pCO2 to 900-1200 µatm pCO2) significantly reduced sperm motility and, to a lesser extent, velocity, which strongly reduced fertilization rates at environmentally relevant sperm concentrations. Normal development of 10 d old larvae was significantly lower under elevated pCO2 but larval size was not significantly different between treatments. Settlement of COTS larvae was significantly reduced on crustose coralline algae (known settlement inducers of COTS) that had been exposed to OA conditions for 85 d prior to settlement assays. Effect size analyses illustrated that reduced settlement may be the largest bottleneck for overall juvenile production. Results indicate that reductions in fertilisation and settlement success alone would reduce COTS population replenishment by over 50%. However, it is unlikely that this effect is sufficient to provide respite for corals from other negative anthropogenic impacts and direct stress from OA and warming on corals.
Star formation history and chemical enrichment in the early Universe: clues from the rest-optical and rest-UV spectra of z~2-3 star-forming galaxies in the Keck Baryonic Structure Survey
Strom, Allison L.
Galaxies at the peak of cosmic star formation (z~2-3) exhibit significantly higher star formation rates and gas fractions at fixed stellar mass than nearby galaxies. These z~2-3 galaxies are also distinct in terms of their nebular spectra, reflecting important differences not only in the physical conditions of their interstellar medium (e.g., electron density and gas-phase metallicity), but also in the details of their massive stellar populations, especially their ionizing radiation fields. Jointly observing galaxies' HII regions, at rest-UV and rest-optical wavelengths, and massive stars, at rest-UV wavelengths, is central to constructing a framework for understanding the differences between z~2-3 and z~0 star-forming galaxies and for self-consistently explaining the trends observed in the high-redshift population. My thesis is based on data from the Keck Baryonic Structure Survey (KBSS), which uniquely combines observations of individual galaxies in these two bandpasses. In total, the near-infrared component of the KBSS includes spectra of >700 z~2-3 galaxies obtained with Keck/MOSFIRE. I will present these results along with a detailed analysis of the full rest-optical (3600-7000 Ang) nebular spectra of ~400 galaxies, showing that high-redshift galaxies exhibit uniformly high degrees of ionization and excitation with respect to most z~0 galaxies. Combined with observations of the same galaxies' rest-UV spectra (obtained with Keck/LRIS) and photoionization model predictions, these results suggest that the disparity arises from differences in the shape of the ionizing radiation field at fixed gas-phase oxygen abundance, most likely due to the effects of Fe-poor massive binary stars. My comprehensive spectroscopic study of an unprecedentedly large sample of z~2-3 galaxies offers compelling evidence that the distinct chemical abundance patterns observed in these galaxies are the result of systematic differences in their star formation histories.
Mesopotamian Star Lists
Horowitz, Wayne
Sumerian and Akkadian names of stars and constellations occur in cuneiform texts for over 2,000 years, from the third millennium BC down to the death of cuneiform in the early first millennium AD, but no fully comprehensive list was ever compiled in antiquity. Lists of stars and constellations are available in both the lexical tradition and astronomical-astrological tradition of the cuneiform scribes. The longest list in the former is that in the series Urra = hubullu, in the latter, those in Mul-Apin.
Star Polymers.
Ren, Jing M; McKenzie, Thomas G; Fu, Qiang; Wong, Edgar H H; Xu, Jiangtao; An, Zesheng; Shanmugam, Sivaprakash; Davis, Thomas P; Boyer, Cyrille; Qiao, Greg G
Recent advances in controlled/living polymerization techniques and highly efficient coupling chemistries have enabled the facile synthesis of complex polymer architectures with controlled dimensions and functionality. As an example, star polymers consist of many linear polymers fused at a central point with a large number of chain end functionalities. Owing to this exclusive structure, star polymers exhibit some remarkable characteristics and properties unattainable by simple linear polymers. Hence, they constitute a unique class of technologically important nanomaterials that have been utilized or are currently under audition for many applications in life sciences and nanotechnologies. This article first provides a comprehensive summary of synthetic strategies towards star polymers, then reviews the latest developments in the synthesis and characterization methods of star macromolecules, and lastly outlines emerging applications and current commercial use of star-shaped polymers. The aim of this work is to promote star polymer research, generate new avenues of scientific investigation, and provide contemporary perspectives on chemical innovation that may expedite the commercialization of new star nanomaterials. We envision in the not-too-distant future star polymers will play an increasingly important role in materials science and nanotechnology in both academic and industrial settings.
APEX/SABOCA observations of small-scale structure of infrared-dark clouds . I. Early evolutionary stages of star-forming cores
Ragan, Sarah E.; Henning, Thomas; Beuther, Henrik
Infrared-dark clouds (IRDCs) harbor the early phases of cluster and high-mass star formation and are comprised of cold (~20 K), dense (n > 104 cm-3) gas. The spectral energy distribution (SED) of IRDCs is dominated by the far-infrared and millimeter wavelength regime, and our initial Herschel study examined IRDCs at the peak of the SED with high angular resolution. Here we present a follow-up study using the SABOCA instrument on APEX which delivers 7.8″ angular resolution at 350 μm, matching the resolution we achieved with Herschel/PACS, and allowing us to characterize substructure on ~0.1 pc scales. Our sample of 11 nearby IRDCs are a mix of filamentary and clumpy morphologies, and the filamentary clouds show significant hierarchical structure, while the clumpy IRDCs exhibit little hierarchical structure. All IRDCs, regardless of morphology, have about 14% of their total mass in small scale core-like structures which roughly follow a trend of constant volume density over all size scales. Out of the 89 protostellar cores we identified in this sample with Herschel, we recover 40 of the brightest and re-fit their SEDs and find their properties agree fairly well with our previous estimates (⟨ T ⟩ ~ 19 K). We detect a new population of "cold cores" which have no 70 μm counterpart, but are 100 and 160 μm-bright, with colder temperatures (⟨ T ⟩ ~ 16 K). This latter population, along with SABOCA-only detections, are predominantly low-mass objects, but their evolutionary diagnostics are consistent with the earliest starless or prestellar phase of cores in IRDCs. Based on observations carried out with the Atacama Pathfinder Experiment (APEX). APEX is a collaboration between Max Planck Institut für Radioastronomie (MPIfR), Onsala Space Observatory (OSO), and the European Southern Observatory (ESO).Appendices are available in electronic form at http://www.aanda.org
Search for OB stars running away from young star clusters. II. The NGC 6357 star-forming region
Gvaramadze, V. V.; Kniazev, A. Y.; Kroupa, P.; Oh, S.
Dynamical few-body encounters in the dense cores of young massive star clusters are responsible for the loss of a significant fraction of their massive stellar content. Some of the escaping (runaway) stars move through the ambient medium supersonically and can be revealed via detection of their bow shocks (visible in the infrared, optical or radio). In this paper, which is the second of a series of papers devoted to the search for OB stars running away from young ( ≲ several Myr) Galactic clusters and OB associations, we present the results of the search for bow shocks around the star-forming region NGC 6357. Using the archival data of the Midcourse Space Experiment (MSX) satellite and the Spitzer Space Telescope, and the preliminary data release of the Wide-Field Infrared Survey Explorer (WISE), we discovered seven bow shocks, whose geometry is consistent with the possibility that they are generated by stars expelled from the young (~1-2 Myr) star clusters, Pismis 24 and AH03 J1725-34.4, associated with NGC 6357. Two of the seven bow shocks are driven by the already known OB stars, HD 319881 and [N78] 34. Follow-up spectroscopy of three other bow-shock-producing stars showed that they are massive (O-type) stars as well, while the 2MASS photometry of the remaining two stars suggests that they could be B0 V stars, provided that both are located at the same distance as NGC 6357. Detection of numerous massive stars ejected from the very young clusters is consistent with the theoretical expectation that star clusters can effectively lose massive stars at the very beginning of their dynamical evolution (long before the second mechanism for production of runaway stars, based on a supernova explosion in a massive tight binary system, begins to operate) and lends strong support to the idea that probably all field OB stars have been dynamically ejected from their birth clusters. A by-product of our search for bow shocks around NGC 6357 is the detection of three circular
Cygnus OB2: Star Formation Ugly Duckling Causes a Flap
Drake, Jeremy J.; Wright, Nicholas; Guarcello, Mario
Cygnus OB2 is one of the largest known OB associations in our Galaxy, with a total stellar mass of 30,000 Msun and boasting an estimated 65 O-type stars and hundreds of OB stars. At a distance of only 1.4kpc, it is also the closest truly massive star forming region and provides a valuable testbed for star and planet formation theory. We have performed a deep stellar census using observations from X-ray to infrared, which has enabled studies of sub-structuring, mass segregation and dynamics, while infrared data reveal a story of protoplanetary disk attrition in an extremely harsh radiation environment. I will discuss how Cygnus OB2 challenges the idea that stars must form in dense, compact clusters, and demonstrates that stars as massive as 100 Msun can form in relatively low-density environments. Convincing evidence of disk photoevaporation poses a potential problem for planet formation and growth in starburst environments.
Structural complexity and wide application of two-dimensional S/O type antimonene
Li, T. T.; He, C.; Zhang, W. X.
Inspired by stable two-dimensional antimonene phases, two new allotropes (S/O and tricycle) antimonenes have been predicted by first-principles calculations in this paper. S/O type antimonene possesses remarkably thermodynamical and dynamical stability, which are comparable to that of buckled type antimonene. The results indicate that S/O type antimonene is a direct band gap semiconductor with a band gap of 2.314 eV and the electronic properties could be effectively tuned by the in-plane strain. In order to explore the potential application, the mechanical properties and optical properties of S/O type antimonene are also extensively studied. It is found the S/O type antimonene is an anisotropic material by the method of analyzing the linear Poisson's ratios and the phonon band structure. These systematical analyses show that S/O type antimonene is a new 2D material with tunable electronic properties, excellent mechanical and optical properties.
A spectroscopic search for colliding stellar winds in O-type close binary systems. I - AO Cassiopeiae
Gies, Douglas R.; Wiggs, Michael S.
AO Cas, a short-period, double-lined spectroscopic binary, is studied as part of a search for spectroscopic evidence of colliding stellar winds in binary systems of O-type stars. High S/N ratio spectra of the H-alpha and He I 6678-A line profiles are presented, and their orbital-phase-related variations are examined in order to derive the location and motions of high-density circumstellar gas in the system. These profile variations are compared with those observed in the UV stellar wind lines in IUE archival spectra. IUE spectra are also used to derive a system mass ratio by constructing cross-correlation functions of a single-lined phase spectrum with each of the other spectra. The resulting mass ratio is consistent with the rotational line broadening of the primary star, if the primary is rotating synchronously with the binary system. The best-fit models were found to have an inclination of 61.1 deg + or - 3.0 deg and have a primary which is close to filling its critical Roche lobe.
A spectroscopic search for colliding stellar winds in O-type close binary systems. III - 29 UW Canis Majoris
The orbital-phase variations in the optical emission lines and UV P Cygni lines of the massive O-type binary 29 UW Canis Majoris are investigated in a search for evidence of colliding winds. High SNR spectra of the H-alpha and He I 6678-A emission lines are presented, and radial velocity curves for several features associated with the photosphere of the more luminous primary star are given. The H-alpha features consists of a P Cygni component that shares the motion of the primary, and which probably originates at the base of its wind, and a broad, stationary emission component. It is proposed that the broad emission forms in a plane midway between the stars where the winds collide. A simple geometric model is used to show that this placement of the broad component can explain the lack of orbital velocity shifts, the near-constancy of the emission strength throughout the orbit, the large velocities associated with the H-alpha wings, and the constancy of the velocity range observed.
Nitrogen line spectroscopy in O-stars. III. The earliest O-stars
Rivero González, J. G.; Puls, J.; Massey, P.; Najarro, F.
Context. The classification scheme proposed by Walborn et al. (2002, AJ, 123, 2754), based primarily on the relative strengths of the N ivλ4058 and N iiiλ4640 emission lines, has been used in a variety of studies to spectroscopically classify early O-type stars. Owing to the lack of a solid theoretical basis, this scheme has not yet been universally accepted though. Aims: We provide first theoretical predictions for the N ivλ4058/N iiiλ4640 emission line ratio in dependence of various parameters, and confront these predictions with results from the analysis of a sample of early-type LMC/SMC O-stars. Methods: Stellar and wind parameters of our sample stars are determined by line profile fitting of hydrogen, helium and nitrogen lines, exploiting the helium and nitrogen ionization balance. Corresponding synthetic spectra are calculated by means of the NLTE atmosphere/spectrum synthesis code fastwind. Results: Though there is a monotonic relationship between the N iv/N iii emission line ratio and the effective temperature, all other parameters being equal, theoretical predictions indicate additional dependencies on surface gravity, mass-loss, metallicity, and, particularly, nitrogen abundance. For a given line ratio (i.e., spectral type), more enriched objects should be typically hotter. These basic predictions are confirmed by results from the alternative model atmosphere code cmfgen. The effective temperatures for the earliest O-stars, inferred from the nitrogen ionization balance, are partly considerably hotter than indicated by previous studies. Consistent with earlier results, effective temperatures increase from supergiants to dwarfs for all spectral types in the LMC. The relation between observed N ivλ4058/N iiiλ4640 emission line ratio and effective temperature, for a given luminosity class, turned out to be quite monotonic for our sample stars, and to be fairly consistent with our model predictions. The scatter within a spectral sub-type is mainly
Hyperfast pulsars as the remnants of massive stars ejected from young star clusters
Gvaramadze, Vasilii V.; Gualandris, Alessia; Portegies Zwart, Simon
Recent proper motion and parallax measurements for the pulsar PSR B1508+55 indicate a transverse velocity of ~1100kms-1, which exceeds earlier measurements for any neutron star. The spin-down characteristics of PSR B1508+55 are typical for a non-recycled pulsar, which implies that the velocity of the pulsar cannot have originated from the second supernova disruption of a massive binary system. The high velocity of PSR B1508+55 can be accounted for by assuming that it received a kick at birth or that the neutron star was accelerated after its formation in the supernova explosion. We propose an explanation for the origin of hyperfast neutron stars based on the hypothesis that they could be the remnants of a symmetric supernova explosion of a high-velocity massive star which attained its peculiar velocity (similar to that of the pulsar) in the course of a strong dynamical three- or four-body encounter in the core of dense young star cluster. To check this hypothesis, we investigated three dynamical processes involving close encounters between: (i) two hard massive binaries, (ii) a hard binary and an intermediate-mass black hole (IMBH) and (iii) a single stars and a hard binary IMBH. We find that main-sequence O-type stars cannot be ejected from young massive star clusters with peculiar velocities high enough to explain the origin of hyperfast neutron stars, but lower mass main-sequence stars or the stripped helium cores of massive stars could be accelerated to hypervelocities. Our explanation for the origin of hyperfast pulsars requires a very dense stellar environment of the order of 106- 107starspc-3. Although such high densities may exist during the core collapse of young massive star clusters, we caution that they have never been observed.
Search for OB stars running away from young star clusters. I. NGC 6611
Gvaramadze, V. V.; Bomans, D. J.
N-body simulations have shown that the dynamical decay of the young (~1 Myr) Orion Nebula cluster could be responsible for the loss of at least half of its initial content of OB stars. This result suggests that other young stellar systems could also lose a significant fraction of their massive stars at the very beginning of their evolution. To confirm this expectation, we used the Mid-Infrared Galactic Plane Survey (completed by the Midcourse Space Experiment satellite) to search for bow shocks around a number of young (⪉several Myr) clusters and OB associations. We discovered dozens of bow shocks generated by OB stars running away from these stellar systems, supporting the idea of significant dynamical loss of OB stars. In this paper, we report the discovery of three bow shocks produced by O-type stars ejected from the open cluster NGC 6611 (M16). One of the bow shocks is associated with the O9.5Iab star HD165319, which was suggested to be one of "the best examples for isolated Galactic high-mass star formation� (de Wit et al. 2005, A&A, 437, 247). Possible implications of our results for the origin of field OB stars are discussed.
How bright planets became dim stars: planetary speculations in John Herschel's double star astronomy.
Case, Stephen
Previous research on the origins of double star astronomy in the early nineteenth century emphasized the role mathematical methods and instrumentation played in motivating early observations of these objects. The work of the British astronomer John Herschel, however, shows that questions regarding the physical nature of double stars were also important. In particular, an analysis of John Herschel's early work on double stars illustrates the way in which speculations regarding these objects were shaped by assumptions of the properties of stars themselves. For Herschel, a major consideration in double star astronomy was distinguishing between types of double stars. Optical doubles were useful in determining parallax while binary doubles were not. In practice, classification of a specific double star pair into one of these categories was based on the assumption that stars were of approximately the same luminosity and thus differences in relative brightness between stars were caused by difference in distances. Such assumptions, though ultimately abandoned, would lead Herschel in the 1830s to advance the possibility that the dim companion stars in certain double star pairs were not stars at all but in fact planets. Copyright © 2014 Elsevier Ltd. All rights reserved.
How bright planets became dim stars: planetary speculations in John Herschel's double star astronomy
Case, S.
Previous research on the origins of double star astronomy in the early nineteenth century emphasized the role mathematical methods and instrumentation played in motivating early observations of these objects. The work of the British astronomer John Herschel, however, shows that questions regarding the physical nature of double stars were also important. In particular, an analysis of John Herschel's early work on double stars illustrates the way in which speculations regarding these objects were shaped by assumptions of the properties of stars themselves. For Herschel, a major consideration in double star astronomy was distinguishing between types of double stars. Optical doubles were useful in determining parallax while binary doubles were not. In practice, classification of a specific double star pair into one of these categories was based on the assumption that stars were of approximately the same luminosity and thus differences in relative brightness between stars were caused by difference in distances. Such assumptions, though ultimately abandoned, would lead Herschel in the 1830s to advance the possibility that the dim companion stars in certain double star pairs were not stars at all but in fact planets.
A home for old stars
This image, taken with the Wide Field Planetary Camera 2 on board the NASA/ESA Hubble Space Telescope, shows the globular cluster Terzan 1. Lying around 20 000 light-years from us in the constellation of Scorpius (The Scorpion), it is one of about 150 globular clusters belonging to our galaxy, the Milky Way. Typical globular clusters are collections of around a hundred thousand stars, held together by their mutual gravitational attraction in a spherical shape a few hundred light-years across. It is thought that every galaxy has a population of globular clusters. Some, like the Milky Way, have a few hundred, while giant elliptical galaxies can have several thousand. They contain some of the oldest stars in a galaxy, hence the reddish colours of the stars in this image — the bright blue ones are foreground stars, not part of the cluster. The ages of the stars in the globular cluster tell us that they were formed during the early stages of galaxy formation! Studying them can also help us to understand how galaxies formed. Terzan 1, like many globular clusters, is a source of X-rays. It is likely that these X-rays come from binary star systems that contain a dense neutron star and a normal star. The neutron star drags material from the companion star, causing a burst of X-ray emission. The system then enters a quiescent phase in which the neutron star cools, giving off X-ray emission with different characteristics, before enough material from the companion builds up to trigger another outburst.
Resolved astrometric orbits of ten O-type binaries
Le Bouquin, J.-B.; Sana, H.; Gosset, E.; De Becker, M.; Duvert, G.; Absil, O.; Anthonioz, F.; Berger, J.-P.; Ertel, S.; Grellmann, R.; Guieu, S.; Kervella, P.; Rabus, M.; Willson, M.
Aims: Our long-term aim is to derive model-independent stellar masses and distances for long period massive binaries by combining apparent astrometric orbit with double-lined radial velocity amplitudes (SB2). Methods: We followed-up ten O+O binaries with AMBER, PIONIER and GRAVITY at the VLTI. Here, we report on 130 astrometric observations over the last seven years. We combined this dataset with distance estimates to compute the total mass of the systems. We also computed preliminary individual component masses for the five systems with available SB2 radial velocities. Results: Nine of the ten binaries have their three-dimensional orbit well constrained. Four of them are known to be colliding wind, non-thermal radio emitters, and thus constitute valuable targets for future high angular resolution radio imaging. Two binaries break the correlation between period and eccentricity tentatively observed in previous studies. This suggests either that massive star formation produces a wide range of systems, or that several binary formation mechanisms are at play. Finally, we found that the use of existing SB2 radial velocity amplitudes can lead to unrealistic masses and distances. Conclusions: If not understood, the biases in radial velocity amplitudes will represent an intrinsic limitation for estimating dynamical masses from SB2+interferometry or SB2+Gaia. Nevertheless, our results can be combined with future Gaia astrometry to measure the dynamical masses and distances of the individual components with an accuracy of 5 to 15%, completely independently of the radial velocities. Based on observations collected with the PIONIER/VLTI, AMBER/VLTI and GRAVITY/VLTI instruments at the European Southern Observatory, Paranal, under programs 087.C-0458, 087.D-0150, 087.D-0264, 090.D-0036, 090.D-0291, 090.D-0600, 091.D-0087, 091.D-0334, 092.C-0243, 092.C-0542, 092.D-0015, 092.D-0366, 092.D-0590, 092.D-0647, 093.C-0503, 093.D-0039, 093.D-0040, 093.D-0673, 094.C-0397, 094.C-0884
Kafatos, M.; Michalitsianos, A. G.
The physical characteristics of symbiotic star systems are discussed, based on a review of recent observational data. A model of a symbiotic star system is presented which illustrates how a cool red-giant star is embedded in a nebula whose atoms are ionized by the energetic radiation from its hot compact companion. UV outbursts from symbiotic systems are explained by two principal models: an accretion-disk-outburst model which describes how material expelled from the tenuous envelope of the red giant forms an inwardly-spiralling disk around the hot companion, and a thermonuclear-outburst model in which the companion is specifically a white dwarf which superheats the material expelled from the red giant to the point where thermonuclear reactions occur and radiation is emitted. It is suspected that the evolutionary course of binary systems is predetermined by the initial mass and angular momentum of the gas cloud within which binary stars are born. Since red giants and Mira variables are thought to be stars with a mass of one or two solar mass, it is believed that the original cloud from which a symbiotic system is formed can consist of no more than a few solar masses of gas.
X-shooter Finds an Extremely Primitive Star
Caffau, E.; Bonifacio, P.; François, P.; Sbordone, L.; Monaco, L.; Spite, M.; Spite, F.; Ludwig, H.-G.; Cayrel, R.; Zaggia, S.; Hammer, F.; Randich, S.; Molaro, P.; Hill, V.
Low-mass extremely metal-poor (EMP) stars hold the fossil record of the chemical composition of the early phases of the Universe in their atmospheres. Chemical analysis of such objects provides important constraints on these early phases. EMP stars are rather rare objects: to dig them out, large amounts of data have to be considered. We have analysed stars from the Sloan Digital Sky Survey using an automatic procedure and selected a sample of good candidate EMP stars, which we observed with the spectrographs X-shooter and UVES. We could confirm the low metallicity of our sample of stars, and we succeeded in finding a record metal-poor star.
B- and A-Type Stars in the Taurus-Auriga Star-Forming Region
Mooley, Kunal; Hillenbrand, Lynne; Rebull, Luisa; Padgett, Deborah; Knapp, Gillian
We describe the results of a search for early-type stars associated with the Taurus-Auriga molecular cloud complex, a diffuse nearby star-forming region noted as lacking young stars of intermediate and high mass. We investigate several sets of possible O, B, and early A spectral class members. The first is a group of stars for which mid-infrared images show bright nebulae, all of which can be associated with stars of spectral-type B. The second group consists of early-type stars compiled from (1) literature listings in SIMBAD, (2) B stars with infrared excesses selected from the Spitzer Space Telescope survey of the Taurus cloud, (3) magnitude- and color-selected point sources from the Two Micron All Sky Survey, and (4) spectroscopically identified early-type stars from the Sloan Digital Sky Survey coverage of the Taurus region. We evaluated stars for membership in the Taurus-Auriga star formation region based on criteria involving: spectroscopic and parallactic distances, proper motions and radial velocities, and infrared excesses or line emission indicative of stellar youth. For selected objects, we also model the scattered and emitted radiation from reflection nebulosity and compare the results with the observed spectral energy distributions to further test the plausibility of physical association of the B stars with the Taurus cloud. This investigation newly identifies as probable Taurus members three B-type stars: HR 1445 (HD 28929), t Tau (HD 29763), 72 Tau (HD 28149), and two A-type stars: HD 31305 and HD 26212, thus doubling the number of stars A5 or earlier associated with the Taurus clouds. Several additional early-type sources including HD 29659 and HD 283815 meet some, but not all, of the membership criteria and therefore are plausible, though not secure, members.
Chameleon stars
Dzhunushaliev, Vladimir; Institute of Physicotechnical Problems and Material Science of the NAS of the Kyrgyz Republic, 265 a, Chui Street, Bishkek, 720071; Folomeev, Vladimir
We consider a gravitating spherically symmetric configuration consisting of a scalar field nonminimally coupled to ordinary matter in the form of a perfect fluid. For this system we find static, regular, asymptotically flat solutions for both relativistic and nonrelativistic cases. It is shown that the presence of the nonminimal interaction leads to substantial changes both in the radial matter distribution of the star and in the star's total mass. A simple stability test indicates that, for the choice of parameters used in the paper, the solutions are unstable.
Toward the first stars: hints from the CEMP-no stars
Choplin, A.
CEMP-no stars are iron-deficient, carbon-rich stars, with no or little s- and r-elements. Because of their very low iron content, they are often considered to be closely linked to the first stars. Their origin is still a matter of debate. Understanding their formation could provide very valuable information on the first stars, early nucleosynthesis, early galactic chemical evolution and first supernovae. The most explored formation scenario for CEMP-no stars suggests that CEMP-no stars formed from the ejecta (wind and/or supernova) of a massive source star, that lived before the CEMP-no star. Here we discuss models of fast rotating massive source stars with and without triggering a late mixing event just before the end of the life of the source star. We find that without this late mixing event, the bulk of observed CEMP-no stars cannot be reproduced by our models. On the opposite, the bulk is reproductible if adding the late mixing event in the source star models.
Star quality.
Dent, Emma
Around 150 wards are participating in the voluntary Star Wards scheme to provide mental health inpatients with more activities with therapeutic value. Suggested activities range from a library, to horse riding Internet access and comedy. Service users are particularly keen to have more exercise, which can be a challenge in inpatient settings.
Star Power
ScienceCinema
The U.S. Department of Energy's Princeton Plasma Physics Laboratory has released ''Star Power,'' a new informational video that uses dramatic and beautiful images and thought-provoking interviews to highlight the importance of the Laboratory's research into magnetic fusion.
VizieR Online Data Catalog: VFTS. O-type stellar content of 30 Dor (Walborn+, 2014)
Walborn, N. R.; Sana, H.; Simon-Diaz, S.; Maiz Apellaniz, J.; Taylor, W. D.; Evans, C. J.; Markova, N.; Lennon, D. J.; de Koter, A.
Detailed spectral classifications are presented for 352 O-B0 stars in the VLT-FLAMES Tarantula Survey ESO Large Programme, of which 213 O-type are judged of sufficiently high quality for further morphological analysis. Among them, six subcategories of special interest are distinguished. (1) Several new examples of the earliest spectral types O2-O3 have been found, while a previously known example has been determined to belong to the nitrogen-rich ON2 class. (2) A group of extremely rapidly rotating main-sequence objects has been isolated, including the largest vsini values known, the spatial and radial-velocity distributions of which suggest ejection from the two principal ionizing clusters NGC 2070 and NGC 2060. (3) Several new examples of the evolved, rapidly rotating Onfp class show similar evidence, although at least some of them are spectroscopic binaries. (4) No fewer than 48 members of the Vz category, hypothesized to be on or near the zero-age main sequence, are found in this sample; in contrast to the rapid rotators, they are strongly concentrated to the ionizing clusters and a newly recognized region of current and recent star formation to the north, supporting their interpretation as very young objects, as do their relatively faint absolute magnitudes. (5) A surprisingly large fraction of the main-sequence spectra belong to the recently recognized V((fc)) class, with CIII emission lines of similar strength to the usual NIII in V((f)) spectra, although a comparable number of the latter are also present, as well as six objects with very high-quality data but no trace of either emission feature, presenting new challenges to physical interpretations. (6) Two mid-O Vz and three late-O giant/supergiant spectra with morphologically enhanced nitrogen lines have been detected. Absolute visual magnitudes have been derived for each star with individual extinction laws, and composite Hertzsprung-Russell diagrams provide evidence of the multiple generations present
A 30 kpc Chain of "Beads on a String" Star Formation between Two Merging Early Type Galaxies in the Core of a Strong-lensing Galaxy Cluster
Tremblay, Grant R.; Gladders, Michael D.; Baum, Stefi A.; O'Dea, Christopher P.; Bayliss, Matthew B.; Cooke, Kevin C.; Dahle, HÃ¥kon; Davis, Timothy A.; Florian, Michael; Rigby, Jane R.; Sharon, Keren; Soto, Emmaris; Wuyts, Eva
New Hubble Space Telescope ultraviolet and optical imaging of the strong-lensing galaxy cluster SDSS J1531+3414 (z = 0.335) reveals two centrally dominant elliptical galaxies participating in an ongoing major merger. The interaction is at least somewhat rich in cool gas, as the merger is associated with a complex network of 19 massive superclusters of young stars (or small tidal dwarf galaxies) separated by ~1 kpc in projection from one another, combining to an estimated total star formation rate of ~5 M ⊙ yr-1. The resolved young stellar superclusters are threaded by narrow Hα, [O II], and blue excess filaments arranged in a network spanning ~27 kpc across the two merging galaxies. This morphology is strongly reminiscent of the well-known "beads on a string" mode of star formation observed on kiloparsec scales in the arms of spiral galaxies, resonance rings, and in tidal tails between interacting galaxies. Nevertheless, the arrangement of this star formation relative to the nuclei of the two galaxies is difficult to interpret in a dynamical sense, as no known "beads on a string" systems associated with kiloparsec-scale tidal interactions exhibit such lopsided morphology relative to the merger participants. In this Letter, we present the images and follow-up spectroscopy and discuss possible physical interpretations for the unique arrangement of the young stellar clusters. While we suggest that this morphology is likely to be dynamically short-lived, a more quantitative understanding awaits necessary multiwavelength follow-up, including optical integral field spectroscopy, ALMA submillimeter interferometry, and Chandra X-ray imaging.
Interacting Star Clusters
Gieles, M.
The early evolution of star cluster formation is a complicated phase in which several astrophysical processes with different time-scales operate simultaneously. From kinematical data of the young massive cluster R136 it was recently found that the cluster is in virial equilibrium; despite its young age it has already settled in a dynamical equilibrium. Somewhat surprisigly, about a quarter of the (kinetic) energy is in a rotational component. From HST observations of R136 a small clump of stars to the North-East of R136 was found, with indications that this clump is interacting/merging with R136. In this talk I will discuss whether these two observational results should be connected, i.e. whether the rotation signal is due to an ongoing "dry" interaction. The results are illustrated with a suite of N-body simulations of R136 like systems.
Sleuthing the Isolated Compact Stars
Drake, J. J.
In the early 1990's, isolated thermally-emitting neutron stars accreting from the interstellar medium were predicted to show up in their thousands in the ROSAT soft X-ray all-sky survey. The glut of sources would provide unprecedented opportunities for probing the equation of state of ultra-dense matter. Only seven objects have been firmly identified to date. The reasons for this discrepency are discussed and recent high resolution X-ray spectroscopic observations of these objects are described. Spectra of the brightest of the isolated neutron star candidates, RX J1856.5-3754, continue to present interpretational difficulties for current neutron star model atmospheres and alternative models are briefly discussed. RX J1856.5-3754 remains a valid quark star candidate.
High-mass Star Formation Toward Southern Infrared Bubble S10
Ranjan Das, Swagat; Tej, Anandmayee; Vig, Sarita; Ghosh, Swarna K.; Ishwara Chandra, C. H.
An investigation in radio and infrared wavelengths of two high-mass star-forming regions toward the southern Galactic bubble S10 is presented here. The two regions under study are associated with the broken bubble S10 and Extended Green Object, G345.99-0.02, respectively. Radio continuum emission mapped at 610 and 1280 MHz using the Giant Metrewave Radio Telescope, India, is detected toward both of the regions. These regions are estimated to be ionized by early-B- to late-O-type stars. Spitzer GLIMPSE mid-infrared data is used to identify young stellar objects (YSOs) associated with these regions. A Class-I/II-type source, with an estimated mass of 6.2 M ⊙, lies ˜7″ from the radio peak. Pixel-wise, modified blackbody fits to the thermal dust emission using Herschel far-infrared data is performed to construct dust temperature and column density maps. Eight clumps are detected in the two regions using the 250 μm image. The masses and linear diameter of these range between ˜300-1600 M ⊙ and 0.2-1.1 pc, respectively, which qualifies them as high-mass star-forming clumps. Modeling of the spectral energy distribution of these clumps indicates the presence of high luminosity, high accretion rate, massive YSOs possibly in the accelerating accretion phase. Furthermore, based on the radio and MIR morphology, the occurrence of a possible bow wave toward the likely ionizing star is explored.
Das, Swagat Ranjan; Tej, Anandmayee; Vig, Sarita
An investigation in radio and infrared wavelengths of two high-mass star-forming regions toward the southern Galactic bubble S10 is presented here. The two regions under study are associated with the broken bubble S10 and Extended Green Object, G345.99-0.02, respectively. Radio continuum emission mapped at 610 and 1280 MHz using the Giant Metrewave Radio Telescope, India, is detected toward both of the regions. These regions are estimated to be ionized by early-B- to late-O-type stars. Spitzer GLIMPSE mid-infrared data is used to identify young stellar objects (YSOs) associated with these regions. A Class-I/II-type source, with an estimated mass of 6.2 M {submore » ⊙}, lies ∼7″ from the radio peak. Pixel-wise, modified blackbody fits to the thermal dust emission using Herschel far-infrared data is performed to construct dust temperature and column density maps. Eight clumps are detected in the two regions using the 250 μ m image. The masses and linear diameter of these range between ∼300–1600 M {sub ⊙} and 0.2–1.1 pc, respectively, which qualifies them as high-mass star-forming clumps. Modeling of the spectral energy distribution of these clumps indicates the presence of high luminosity, high accretion rate, massive YSOs possibly in the accelerating accretion phase. Furthermore, based on the radio and MIR morphology, the occurrence of a possible bow wave toward the likely ionizing star is explored.« less
Spectroscopic studies of Wolf-Rayet stars with absorption lines. VIII - HD 193793
Conti, P. S.; Dupre, D. Roussel; Massey, P.; Rensing, M.
The authors present absorption-line velocities for the O type star spanning over 16 years and emission-line velocities for the WC star covering 10 years. They find no periodicities in either of these sets of data. In particular, they are unable to confirm the claim of Lamontagne, Moffat, and Seggewiss that the two stars are in orbit about one another. Rather, it seems that a generic relationship between the two components has not been established and one is dealing with a situation in which two stars are in the same line of sight.
Weighing the Smallest Stars
in large telescopes. Astronomers have however found ways to overcome this difficulty. For this, they rely on a combination of a well-considered observational strategy with state-of-the-art instruments. High contrast camera First, astronomers searching for very low mass objects look at young nearby stars because low-mass companion objects will be brightest while they are young, before they contract and cool off. In this particular case, an international team of astronomers [1] led by Laird Close (Steward Observatory, University of Arizona), studied the star AB Doradus A (AB Dor A). This star is located about 48 light-years away and is "only" 50 million years old. Because the position in the sky of AB Dor A "wobbles", due to the gravitational pull of a star-like object, it was believed since the early 1990s that AB Dor A must have a low-mass companion. To photograph this companion and obtain a comprehensive set of data about it, Close and his colleagues used a novel instrument on the European Southern Observatory's Very Large Telescope. This new high-contrast adaptive optics camera, the NACO Simultaneous Differential Imager, or NACO SDI [2], was specifically developed by Laird Close and Rainer Lenzen (Max-Planck-Institute for Astronomy in Heidelberg, Germany) for hunting extrasolar planets. The SDI camera enhances the ability of the VLT and its adaptive optics system to detect faint companions that would normally be lost in the glare of the primary star. A world premiere ESO PR Photo 03/05 ESO PR Photo 03/05 Infrared image of AB Doradus A and its companion [Preview - JPEG: 400 x 406 pix - 99k] [Normal - JPEG: 800 x 812 pix - 235k] Caption: ESO PR Photo 03/05 is an enhanced, false-colour near-infrared image of AB Dor A and C. The faint companion "AB Dor C" - seen as the pink dot at 8 o'clock - is 120 times fainter than its primary star. The tiny separation between A and C, only 0.156 arcsec, is smaller than a one Euro coin seen at 20 km distance. Nevertheless, the new
Converting neutron stars into strange stars
Olinto, A. V.
If strange matter is formed in the interior of a neutron star, it will convert the entire neutron star into a strange star. The proposed mechanisms are reviewed for strange matter seeding and the possible strange matter contamination of neutron star progenitors. The conversion process that follows seeding and the recent calculations of the conversion timescale are discussed.
Heavy Metal Stars
La Silla Telescope Detects Lots of Lead in Three Distant Binaries Summary Very high abundances of the heavy element Lead have been discovered in three distant stars in the Milky Way Galaxy . This finding strongly supports the long-held view that roughly half of the stable elements heavier than Iron are produced in common stars during a phase towards the end of their life when they burn their Helium - the other half results from supernova explosions. All the Lead contained in each of the three stars weighs about as much as our Moon. The observations show that these "Lead stars" - all members of binary stellar systems - have been more enriched with Lead than with any other chemical element heavier than Iron. This new result is in excellent agreement with predictions by current stellar models about the build-up of heavy elements in stellar interiors. The new observations are reported by a team of Belgian and French astronomers [1] who used the Coude Echelle Spectrometer on the ESO 3.6-m telescope at the La Silla Observatory (Chile). PR Photo 26a/01 : A photo of HD 196944 , one of the "Lead stars". PR Photo 26b/01 : A CES spectrum of HD 196944 . The build-up of heavy elements Astronomers and physicists denote the build-up of heavier elements from lighter ones as " nucleosynthesis ". Only the very lightest elements (Hydrogen, Helium and Lithium [2]) were created at the time of the Big Bang and therefore present in the early universe. All the other heavier elements we now see around us were produced at a later time by nucleosynthesis inside stars. In those "element factories", nuclei of the lighter elements are smashed together whereby they become the nuclei of heavier ones - this process is known as nuclear fusion . In our Sun and similar stars, Hydrogen is being fused into Helium. At some stage, Helium is fused into Carbon, then Oxygen, etc. The fusion process requires positively charged nuclei to move very close to each other before they can unite. But with increasing
PRISM Polarimetry of Massive Stars
Kerkstra, Brennan; Lomax, Jamie R.; Bjorkman, Karen S.; Bjorkman, Jon Eric; Skiff, Brian; Covey, Kevin R.; Wisniewski, John P.
We present the early results from our long-term, multi-epoch filter polarization survey of massive stars in and around young Galactic clusters. These BVRI polarization data were obtained using the PRISM instrument mounted on the 1.8m Perkins Telescope at Lowell Observatory. We first detail the creation of our new semi-automated polarization data reduction pipeline that we developed to process these data. Next, we present our analysis of the instrumental polarization properties of the PRISM instrument, via observations of polarized and unpolarized standard stars. Finally, we present early results on the total and intrinsic polarization behavior of several isolated, previously suggested classical Be stars, and discuss these results in the context of the larger project.BK acknowledges support from a NSF/REU at the University of Oklahoma. This program was also supported by NSF-AST 11411563, 1412110, and 1412135.
StarBright Learning Exchange
This article features StarBright Learning Exchange, a program that provides a cross-cultural exchange between Australian and South African early childhood educators. The program was originated when its president, Carol Allen, and her colleague, Karen Williams, decided that they could no longer sit by and watch the unfolding social catastrophe that…
The ALMA early science view of FUor/EXor objects - IV. Misaligned outflows in the complex star-forming environment of V1647 Ori and McNeil's Nebula
Principe, David A.; Cieza, Lucas; Hales, Antonio; Zurlo, Alice; Williams, Jonathan; Ruíz-Rodríguez, Dary; Canovas, Hector; Casassus, Simon; Mužić, Koraljka; Perez, Sebastian; Tobin, John J.; Zhu, Zhaohuan
We present Atacama Large Millimeter/sub-millimeter Array (ALMA) observations of the star-forming environment surrounding V1647 Ori, an outbursting FUor/EXor pre-main sequence star. Dust continuum and the (J = 2 - 1) 12CO, 13CO, C18O molecular emission lines were observed to characterize the V1647 Ori circumstellar disc and any large scale molecular features present. We detect continuum emission from the circumstellar disc and determine a radius r = 40 au, inclination i = 17°+6-9 and total disc mass of Mdisc of ∼0.1 M⊙. We do not identify any disc structures associated with nearby companions, massive planets or fragmentation. The molecular cloud environment surrounding V1647 Ori is both structured and complex. We confirm the presence of an excavated cavity north of V1647 Ori and have identified dense material at the base of the optical reflection nebula (McNeil's Nebula) that is actively shaping its surrounding environment. Two distinct outflows have been detected with dynamical ages of ∼11 700 and 17 200 yr. These outflows are misaligned suggesting disc precession over ∼5500 yr as a result of anisotropic accretion events is responsible. The collimated outflows exhibit velocities of ∼2 km s-1, similar in velocity to that of other FUor objects presented in this series, but significantly slower than previous observations and model predictions. The V1647 Ori system is seemingly connected by an 'arm' of material to a large unresolved structure located ∼20 arcsec to the west. The complex environment surrounding V1647 Ori suggests it is in the early stages of star formation, which may relate to its classification as both a FUor and EXor type object.
Star ratings. Stars of wonder.
Dawes, David
Analysis of trusts that changed their star-rating over the past two years indicates that a change of chief executive was not a significant factor. The length of time in post and the experience of the chief executive were also insignificant. This has serious implications for the theory behind franchising and the evaluation of franchised trusts. Holding chief executives to account for the organisation's performance within their first 12 months is unlikely to be effective.
VizieR Online Data Catalog: Massive LMC stars AAOmega spectroscopy (Evans+, 2015)
Evans, C. J.; van Loon, J. T.; Hainich, R.; Bailey, M.
This catalogue comprises ascii versions of the optical spectra of 263 massive stars in the Large Magellanic Cloud, obtained with the AAOmega spectrograph on the Anglo Australian Telescope. Spectra from the first night (2006 Feb 22) were obtained with a 1700B grating at two wavelength settings. The spectra published here were obtained by median combining the two exposures at both settings, and then median combining them in the overlap region (spanning ~4375-4400Ã…). Spectra from the second night (2006 Feb 23) were obtained with a 1500V grating at one central wavelength setting (4375Ã…). The spectra The published spectra have been normalised/rectified using an automated script, which uses pre-defined regions (selected to avoid known absorption lines in early-type stars) to create a polynomial fit to the notional continuum in each spectrum. The published spectra have been divided by those fits to rectify them to unity. As such, we caution the user that quantitative analysis of these data would benefit from tailored rectification of the spectra. In particular, at the ends of the spectral range, and across broad emission features (such as that around HeII 4686 in luminous O-type supergiants). Also note that there were a number of 'hot' columns in the AAOmega CCDs, leading to small breaks (at multiple wavelengths) in the large majority of the spectra. (5 data files).
Spheroidal Populated Star Systems
Angeletti, Lucio; Giannone, Pietro
Globular clusters and low-ellipticity early-type galaxies can be treated as systems populated by a large number of stars and whose structures can be schematized as spherically symmetric. Their studies profit from the synthesis of stellar populations. The computation of synthetic models makes use of various contributions from star evolution and stellar dynamics. In the first sections of the paper we present a short review of our results on the occurrence of galactic winds in star systems ranging from globular clusters to elliptical galaxies, and the dynamical evolution of a typical massive globular cluster. In the subsequent sections we describe our approach to the problem of the stellar populations in elliptical galaxies. The projected radial behaviours of spectro-photometric indices for a sample of eleven galaxies are compared with preliminary model results. The best agreement between observation and theory shows that our galaxies share a certain degree of heterogeneity. The gas energy dissipation varies from moderate to large, the metal yield ranges from solar to significantly oversolar, the dispersion of velocities is isotropic in most of the cases and anisotropic in the remaining instances.
THE PREVALENCE AND IMPACT OF WOLF–RAYET STARS IN EMERGING MASSIVE STAR CLUSTERS
Sokal, Kimberly R.; Johnson, Kelsey E.; Indebetouw, Rémy
We investigate Wolf–Rayet (WR) stars as a source of feedback contributing to the removal of natal material in the early evolution of massive star clusters. Despite previous work suggesting that massive star clusters clear out their natal material before the massive stars evolve into the WR phase, WR stars have been detected in several emerging massive star clusters. These detections suggest that the timescale for clusters to emerge can be at least as long as the time required to produce WR stars (a few million years), and could also indicate that WR stars may be providing the tipping point inmore » the combined feedback processes that drive a massive star cluster to emerge. We explore the potential overlap between the emerging phase and the WR phase with an observational survey to search for WR stars in emerging massive star clusters hosting WR stars. We select candidate emerging massive star clusters from known radio continuum sources with thermal emission and obtain optical spectra with the 4 m Mayall Telescope at Kitt Peak National Observatory and the 6.5 m MMT.{sup 4} We identify 21 sources with significantly detected WR signatures, which we term "emerging WR clusters.� WR features are detected in ∼50% of the radio-selected sample, and thus we find that WR stars are commonly present in currently emerging massive star clusters. The observed extinctions and ages suggest that clusters without WR detections remain embedded for longer periods of time, and may indicate that WR stars can aid, and therefore accelerate, the emergence process.« less
OBSERVATIONAL SIGNATURES OF CONVECTIVELY DRIVEN WAVES IN MASSIVE STARS
Aerts, C.; Rogers, T. M.
We demonstrate observational evidence for the occurrence of convectively driven internal gravity waves (IGWs) in young massive O-type stars observed with high-precision CoRoT space photometry. This evidence results from a comparison between velocity spectra based on two-dimensional hydrodynamical simulations of IGWs in a differentially rotating massive star and the observed spectra. We also show that the velocity spectra caused by IGWs may lead to detectable line-profile variability and explain the occurrence of macroturbulence in the observed line profiles of OB stars. Our findings provide predictions that can readily be tested by including a sample of bright, slowly and rapidly rotatingmore » OB-type stars in the scientific program of the K2 mission accompanied by high-precision spectroscopy and their confrontation with multi-dimensional hydrodynamic simulations of IGWs for various masses and ages.« less
Keepers of the double stars
Tenn, Joseph S.
Astronomers have long tracked double stars in efforts to find those that are gravitationally-bound binaries and then to determine their orbits. Early catalogues by the Herschels, Struves, and others began with their own discoveries. In 1906 court reporter and amateur astronomer Sherburne Wesley Burnham published a massive double star catalogue containing data from many observers on more than 13,000 systems. Lick Observatory astronomer Robert Grant Aitken produced a much larger catalogue in 1932 and coordinated with Robert Innes of Johannesburg, who catalogued the southern systems. Aitken maintained and expanded Burnham's records of observations on handwritten file cards, and eventually turned them over to the Lick Observatory, where astrometrist Hamilton Jeffers further expanded the collection and put all the observations on punched cards. With the aid of Frances M. "Rete" Greeby he made two catalogues: an Index Catalogue with basic data about each star, and a complete catalogue of observations, with one observation per punched card. He enlisted Willem van den Bos of Johannesburg to add southern stars, and together they published the Index Catalogue of Visual Double Stars, 1961.0. As Jeffers approached retirement he became greatly concerned about the disposition of the catalogues. He wanted to be replaced by another "double star man," but Lick Director Albert E. Whitford had the new 120-inch reflector, the world's second largest telescope, and he wanted to pursue modern astrophysics instead. Jeffers was vociferously opposed to turning over the card files to another institution, and especially against their coming under the control of Kaj Strand of the United States Naval Observatory. In the end the USNO got the files and has maintained the records ever since, first under Charles Worley, and, since 1997, under Brian Mason. Now called the Washington Double Star Catalog (WDS), it is completely online and currently contains more than 1,200,000 measures of more than 125
Atoms, Stars, and Nebulae
Aller, Lawrence H.
1. Introducing stars and nebulae; 2. Stellar rainbows; 3. Atoms and molecules; 4. The climate in a stellar atmosphere; 5. Analysing the stars; 6. Dwarfs, giants, and supergiants; 7. What makes a star shine?; 8. The youth and middle age of a common star; 9. Wind, dust and pulsations; 10. A star's last hurray?; 11. The interstellar medium and gaseous nebulae; 12. Uncommon stars and their sometimes violent behaviour; 13. High energy astronomy.
The Multiplicity of Massive Stars: A High Angular Resolution Survey With The HST Fine Guidance Sensor
al. (2014), and of the Large Magellanic Cloud (LMC) Tarantula Nebula region by Sana et al. (2013b), demonstrate that the binary frequency may be »70...Monte-Carlo method to fit spectroscopic results for a large sample of O-type stars in the Tarantula Nebula region of the LMC, and they find a best fit
Kitchin, Chris; Forrest, Robert W.
Seeing Stars is written for astronomers, regardless of the depth of their theoretical knowledge, who are taking their first steps in observational astronomy. Chris Kitchin and Bob Forrest - both professional astronomers - take a conducted tour of the night sky and suggest suitable observing programmes for everyone from beginners to experts. How is this book different? We are all familiar with the beautiful images of planets and galaxies obtained by spacecraft and giant telescopes - but what can you really see with a small telescope? What should you expect from a small refractor or reflector? And what is the effect of observing from a site near a city? The answers are all here, with many photographs that will illustrate exactly what can be seen with different instruments (everything from the naked eye to a 300mm telescope) - and from different locations.
Ice Stars
Ice Stars - August 4th, 2002 Description: Like distant galaxies amid clouds of interstellar dust, chunks of sea ice drift through graceful swirls of grease ice in the frigid waters of Foxe Basin near Baffin Island in the Canadian Arctic. Sea ice often begins as grease ice, a soupy slick of tiny ice crystals on the ocean's surface. As the temperature drops, grease ice thickens and coalesces into slabs of more solid ice. Credit: USGS/NASA/Landsat 7 To learn more about the Landsat satellite go to: landsat.gsfc.nasa.gov/ NASA Goddard Space Flight Center enables NASA's mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA's accomplishments by contributing compelling scientific knowledge to advance the Agency's mission. Follow us on Twitter Join us on Facebook
Stellar Archaeology: New Science with Old Stars
The early chemical evolution of the Galaxy and the Universe is vital to our understanding of a host of astrophysical phenomena. Since the most metal-poor Galactic stars are relics from the high-redshift Universe, they probe the chemical and dynamical conditions as the Milky Way began to form, the origin and evolution of the elements, and the physics of nucleosynthesis. They also provide constraints on the nature of the first stars, their associated supernovae and initial mass function, and early star and galaxy formation. I will present exemplary metal-poor stars with which these different topics can be addressed. Those are the most metal-poor stars in the Galaxy ([Fe/H] < -5.0), and metal-poor stars with strong overabundances of heavy elements, in particular uranium and thorium, which can be used to radioactively date the stars to be 13 Gyr old. I will then transition to recent discoveries of metal-poor ([Fe/H] -3.0) stars in the least luminous dwarf satellites orbiting the Milky Way. Their stellar chemical signatures support the concept that small systems, analogous to the surviving dwarf galaxies, were the building blocks of the Milky Way's low-metallicity halo. This opens a new window for studying galaxy formation through stellar chemistry.
Anomalous hydrodynamics kicks neutron stars
Kaminski, Matthias; Uhlemann, Christoph F.; Bleicher, Marcus; ...
Observations show that, at the beginning of their existence, neutron stars are accelerated briskly to velocities of up to a thousand kilometers per second. We argue that this remarkable effect can be explained as a manifestation of quantum anomalies on astrophysical scales. To theoretically describe the early stage in the life of neutron stars we use hydrodynamics as a systematic effective-field-theory framework. Within this framework, anomalies of the Standard Model of particle physics as underlying microscopic theory imply the presence of a particular set of transport terms, whose form is completely fixed by theoretical consistency. Here, the resulting chiral transportmore » effects in proto-neutron stars enhance neutrino emission along the internal magnetic field, and the recoil can explain the order of magnitude of the observed kick velocities.« less
The evolution of massive stars and their spectra. I. A non-rotating 60 M⊙ star from the zero-age main sequence to the pre-supernova stage
Groh, Jose H.; Meynet, Georges; Ekström, Sylvia; Georgy, Cyril
For the first time, the interior and spectroscopic evolution of a massive star is analyzed from the zero-age main sequence (ZAMS) to the pre-supernova (SN) stage. For this purpose, we combined stellar evolution models using the Geneva code and stellar atmospheric/wind models using CMFGEN. With our approach, we were able to produce observables, such as a synthetic high-resolution spectrum and photometry, thereby aiding the comparison between evolution models and observed data. Here we analyze the evolution of a non-rotating 60 M⊙ star and its spectrum throughout its lifetime. Interestingly, the star has a supergiant appearance (luminosity class I) even at the ZAMS. We find the following evolutionary sequence of spectral types: O3 I (at the ZAMS), O4 I (middle of the H-core burning phase), B supergiant (BSG), B hypergiant (BHG), hot luminous blue variable (LBV; end of H-core burning), cool LBV (H-shell burning through the beginning of the He-core burning phase), rapid evolution through late WN and early WN, early WC (middle of He-core burning), and WO (end of He-core burning until core collapse). We find the following spectroscopic phase lifetimes: 3.22 × 106 yr for the O-type, 0.34 × 105 yr (BSG), 0.79 × 105 yr (BHG), 2.35 × 105 yr (LBV), 1.05 × 105 yr (WN), 2.57 × 105 yr (WC), and 3.80 × 104 yr (WO). Compared to previous studies, we find a much longer (shorter) duration for the early WN (late WN) phase, as well as a long-lived LBV phase. We show that LBVs arise naturally in single-star evolution models at the end of the MS when the mass-loss rate increases as a consequence of crossing the bistability limit. We discuss the evolution of the spectra, magnitudes, colors, and ionizing flux across the star's lifetime, and the way they are related to the evolution of the interior. We find that the absolute magnitude of the star typically changes by ~6 mag in optical filters across the evolution, with the star becoming significantly fainter in optical filters at
Kinematic evidence for feedback-driven star formation in NGC 1893
Lim, Beomdu; Sung, Hwankyung; Bessell, Michael S.; Lee, Sangwoo; Lee, Jae Joon; Oh, Heeyoung; Hwang, Narae; Park, Byeong-Gon; Hur, Hyeonoh; Hong, Kyeongsoo; Park, Sunkyung
OB associations are the prevailing star-forming sites in the Galaxy. Up to now, the process of how OB associations were formed remained a mystery. A possible process is self-regulating star formation driven by feedback from massive stars. However, although a number of observational studies uncovered various signposts of feedback-driven star formation, the effectiveness of such feedback has been questioned. Stellar and gas kinematics is a promising tool to capture the relative motion of newborn stars and gas away from ionizing sources. We present high-resolution spectroscopy of stars and gas in the young open cluster NGC 1893. Our findings show that newborn stars and the tadpole nebula Sim 130 are moving away from the central cluster containing two O-type stars, and that the time-scale of sequential star formation is about 1 Myr within a 9 pc distance. The newborn stars formed by feedback from massive stars account for at least 18 per cent of the total stellar population in the cluster, suggesting that this process can play an important role in the formation of OB associations. These results support the self-regulating star formation model.
Gravitational wave asteroseismology with protoneutron stars
Sotani, Hajime; Takiwaki, Tomoya
We examine the time evolution of the frequencies of the gravitational wave after the bounce within the framework of relativistic linear perturbation theory using the results of one-dimensional numerical simulations of core-collapse supernovae. Protoneutron star models are constructed in such a way that the mass and the radius of the protoneutron star become equivalent to the results obtained from the numerical simulations. Then we find that the frequencies of gravitational waves radiating from protoneutron stars strongly depend on the mass and the radius of protoneutron stars, but almost independently of the profiles of the electron fraction and the entropy per baryon inside the star. Additionally, we find that the frequencies of gravitational waves can be characterized by the square root of the average density of the protoneutron star irrespective of the progenitor models, which are completely different from the empirical formula for cold neutron stars. The dependence of the spectra on the mass and the radius is different from that of the g -mode: the oscillations around the surface of protoneutron stars due to the convection and the standing accretion-shock instability. Careful observation of these modes of gravitational waves can determine the evolution of the mass and the radius of protoneutron stars after core bounce. Furthermore, the expected frequencies of gravitational waves are around a few hundred hertz in the early stages after bounce, which must be a good candidate for the ground-based gravitational wave detectors.
O stars and Wolf-Rayet stars
Conti, Peter S.; Underhill, Anne B.; Jordan, Stuart (Editor); Thomas, Richard (Editor)
Basic information is given about O and Wolf-Rayet stars indicating how these stars are defined and what their chief observable properties are. Part 2 of the volume discussed four related themes pertaining to the hottest and most luminous stars. Presented are: an observational overview of the spectroscopic classification and extrinsic properties of O and Wolf-Rayet stars; the intrinsic parameters of luminosity, effective temperature, mass, and composition of the stars, and a discussion of their viability; stellar wind properties; and the related issues concerning the efforts of stellar radiation and wind on the immediate interstellar environment are presented.
Egyptian "Star Clocks"
Symons, Sarah
Diagonal, transit, and Ramesside star clocks are tables of astronomical information occasionally found in ancient Egyptian temples, tombs, and papyri. The tables represent the motions of selected stars (decans and hour stars) throughout the Egyptian civil year. Analysis of star clocks leads to greater understanding of ancient Egyptian constellations, ritual astronomical activities, observational practices, and pharaonic chronology.
Lifestyles of the Stars.
National Aeronautics and Space Administration, Cocoa Beach, FL. John F. Kennedy Space Center.
Some general information on stars is provided in this National Aeronautics and Space Administration pamphlet. Topic areas briefly discussed are: (1) the birth of a star; (2) main sequence stars; (3) red giants; (4) white dwarfs; (5) neutron stars; (6) supernovae; (7) pulsars; and (8) black holes. (JN)
The VLT-FLAMES Tarantula Survey. XVI. The optical and NIR extinction laws in 30 Doradus and the photometric determination of the effective temperatures of OB stars
Maíz Apellániz, J.; Evans, C. J.; Barbá, R. H.; Gräfener, G.; Bestenlehner, J. M.; Crowther, P. A.; García, M.; Herrero, A.; Sana, H.; Simón-Díaz, S.; Taylor, W. D.; van Loon, J. Th.; Vink, J. S.; Walborn, N. R.
Context. The commonly used extinction laws of Cardelli et al. (1989, ApJ, 345, 245) have limitations that, among other issues, hamper the determination of the effective temperatures of O and early B stars from optical and near-infrared (NIR) photometry. Aims: We aim to develop a new family of extinction laws for 30 Doradus, check their general applicability within that region and elsewhere, and apply them to test the feasibility of using optical and NIR photometry to determine the effective temperature of OB stars. Methods: We use spectroscopy and NIR photometry from the VLT-FLAMES Tarantula Survey and optical photometry from HST/WFC3 of 30 Doradus and we analyze them with the software code CHORIZOS using different assumptions, such as the family of extinction laws. Results: We derive a new family of optical and NIR extinction laws for 30 Doradus and confirm its applicability to extinguished Galactic O-type systems. We conclude that by using the new extinction laws it is possible to measure the effective temperatures of OB stars with moderate uncertainties and only a small bias, at least up to E(4405-5495) ~ 1.5 mag. Appendices are available in electronic form at http://www.aanda.org
Early Soft X-Ray to UV Emission from Double Neutron Star Mergers: Implications from the Long-term Observations of GW170817
Wang, Xiang-Yu; Huang, Zhi-Qiu
Recent long-term radio follow-up observations of GW170817 reveal a simple power-law rising light curve, with a slope of {t}0.78, up to 93 days after the merger. The latest X-ray detection at 109 days is also consistent with such a temporal slope. Such a shallow rise behavior requires a mildly relativistic outflow with a steep velocity gradient profile, so that slower material with larger energy catches up with the decelerating ejecta and re-energizes it. It has been suggested that this mildly relativistic outflow may represent a cocoon of material. We suggest that the velocity gradient profile may form during the stage that the cocoon is breaking out of the merger ejecta, resulting from shock propagation down a density gradient. The cooling of the hot relativistic cocoon material immediately after it breaks out should have produced soft X-ray to UV radiation at tens of seconds to hours after the merger. The soft X-ray emission has a luminosity of {L}{{X}}∼ {10}45 {erg} {{{s}}}-1 over a period of tens of seconds for a merger event like GW170817. The UV emission shows a rise initially and peaks at about a few hours with a luminosity of {L}{UV}∼ {10}42 {erg} {{{s}}}-1. The soft X-ray transients could be detected by future wide-angle X-ray detectors, such as the Chinese mission Einstein Probe. This soft X-ray/UV emission would serve as one of the earliest electromagnetic counterparts of gravitation waves from double neutron star mergers and could provide the earliest localization of the sources.
Spectroscopic detections of C III] λ1909 Å at z ≃ 6-7: a new probe of early star-forming galaxies and cosmic reionization
Stark, Daniel P.; Richard, Johan; Charlot, Stéphane; Clément, Benjamin; Ellis, Richard; Siana, Brian; Robertson, Brant; Schenker, Matthew; Gutkin, Julia; Wofford, Aida
Deep spectroscopic observations of z ≳ 6.5 galaxies have revealed a marked decline with increasing redshift in the detectability of Ly α emission. While this may offer valuable insight into the end of the reionization process, it presents a challenge to the detailed spectroscopic study of bright photometrically-selected distant sources now being found via deep Hubble Space Telescope imaging, and particularly those highly magnified sources viewed through foreground lensing clusters. In this paper, we demonstrate the validity of a new way forward via the detection of an alternative diagnostic line, C III] λ1909 Å, seen in spectroscopic exposures of a star-forming galaxy at zLyα = 6.029. We also report tentative detection of C III] λ1909 Å in a galaxy at zLyα = 7.213. The former 3.3σ detection is based on a 3.5 h XShooter spectrum of a bright (J125 = 25.2) gravitationally-lensed galaxy behind the cluster Abell 383. The latter 2.8σ detection is based on a 4.2 h MOSFIRE spectra of one of the most distant spectroscopically confirmed galaxies, GN-108036, with J140 = 25.2. Both targets were chosen for their continuum brightness and previously-known redshift (based on Ly α), ensuring that any C III] emission would be located in a favourable portion of the near-infrared sky spectrum. Since the availability of secure Ly α redshifts significantly narrows the wavelength range where C III] is sought, this increases confidence in these, otherwise, low-signal-to-noise ratio detections. We compare our C III] and Ly α equivalent widths in the context of those found at z ≃ 2 from earlier work and discuss the motivation for using lines other than Ly α to study galaxies in the reionization era.
Compact stars
Estevez-Delgado, Gabino; Estevez-Delgado, Joaquin
An analysis and construction is presented for a stellar model characterized by two parameters (w, n) associated with the compactness ratio and anisotropy, respectively. The reliability range for the parameter w ≤ 1.97981225149 corresponds with a compactness ratio u ≤ 0.2644959374, the density and pressures are positive, regular and monotonic decrescent functions, the radial and tangential speed of sound are lower than the light speed, moreover, than the plausible stability. The behavior of the speeds of sound are determinate for the anisotropy parameter n, admitting a subinterval where the speeds are monotonic crescent functions and other where we have monotonic decrescent functions for the same speeds, both cases describing a compact object that is also potentially stable. In the bigger value for the observational mass M = 2.05 M⊙ and radii R = 12.957 Km for the star PSR J0348+0432, the model indicates that the maximum central density �c = 1.283820319 × 1018 Kg/m3 corresponds to the maximum value of the anisotropy parameter and the radial and tangential speed of the sound are monotonic decrescent functions.
Neutron Stars and NuSTAR
Bhalerao, Varun
My thesis centers around the study of neutron stars, especially those in massive binary systems. To this end, it has two distinct components: the observational study of neutron stars in massive binaries with a goal of measuring neutron star masses and participation in NuSTAR, the first imaging hard X-ray mission, one that is extremely well suited to the study of massive binaries and compact objects in our Galaxy. The Nuclear Spectroscopic Telescope Array (NuSTAR) is a NASA Small Explorer mission that will carry the first focusing high energy X-ray telescope to orbit. NuSTAR has an order-of-magnitude better angular resolution and has two orders of magnitude higher sensitivity than any currently orbiting hard X-ray telescope. I worked to develop, calibrate, and test CdZnTe detectors for NuSTAR. I describe the CdZnTe detectors in comprehensive detail here - from readout procedures to data analysis. Detailed calibration of detectors is necessary for analyzing astrophysical source data obtained by the NuSTAR. I discuss the design and implementation of an automated setup for calibrating flight detectors, followed by calibration procedures and results. Neutron stars are an excellent probe of fundamental physics. The maximum mass of a neutron star can put stringent constraints on the equation of state of matter at extreme pressures and densities. From an astrophysical perspective, there are several open questions in our understanding of neutron stars. What are the birth masses of neutron stars? How do they change in binary evolution? Are there multiple mechanisms for the formation of neutron stars? Measuring masses of neutron stars helps answer these questions. Neutron stars in high-mass X-ray binaries have masses close to their birth mass, providing an opportunity to disentangle the role of "nature" and "nurture" in the observed mass distributions. In 2006, masses had been measured for only six such objects, but this small sample showed the greatest diversity in masses
No Evidence for Protoplanetary Disk Destruction By OB Stars in the MYStIX Sample
Richert, Alexander J. W.; Feigelson, Eric D.; Getman, Konstantin V.; Kuhn, Michael A.
Hubble Space Telescope images of proplyds in the Orion Nebula, as well as submillimeter/radio measurements, show that the dominant O7 star {θ }1Ori C photoevaporates nearby disks around pre-main-sequence stars. Theory predicts that massive stars photoevaporate disks within distances of the order of 0.1 pc. These findings suggest that young, OB-dominated massive H ii regions are inhospitable to the survival of protoplanetary disks and, subsequently, to the formation and evolution of planets. In the current work, we test this hypothesis using large samples of pre-main-sequence stars in 20 massive star-forming regions selected with X-ray and infrared photometry in the MYStIX survey. Complete disk destruction would lead to a deficit of cluster members with an excess in JHKS and Spitzer/IRAC bands in the vicinity of O stars. In four MYStIX regions containing O stars and a sufficient surface density of disk-bearing sources to reliably test for spatial avoidance, we find no evidence for the depletion of inner disks around pre-main-sequence stars in the vicinity of O-type stars, even very luminous O2-O5 stars. These results suggest that massive star-forming regions are not very hostile to the survival of protoplanetary disks and, presumably, to the formation of planets.
The nature of Becklin's star.
Penston, M. V.; Allen, D. A.; Hyland, A. R.
The IR point source in the Orion Nebula commonly known as Becklin's star appears to be exceptional because of its extreme colors and the lack of any associated optical object. Characteristics of the spectrum of Becklin's object are examined. It is found that the spectrum is consistent with that of a highly reddened early-type supergiant, in which weak absorption has been masked by low resolution.
Extreme isolation of WN3/O3 stars and implications for their evolutionary origin as the elusive stripped binaries
Smith, Nathan; Götberg, Ylva; de Mink, Selma E.
Recent surveys of the Magellanic Clouds have revealed a subtype of Wolf-Rayet (WR) star with peculiar properties. WN3/O3 spectra exhibit both WR-like emission and O3 V-like absorption - but at lower luminosity than O3 V or WN stars. We examine the projected spatial distribution of WN3/O3 stars in the Large Magellanic Cloud as compared to O-type stars. Surprisingly, WN3/O3 stars are among the most isolated of all classes of massive stars; they have a distribution similar to red supergiants dominated by initial masses of 10-15 M⊙, and are far more dispersed than classical WR stars or luminous blue variables. Their lack of association with clusters of O-type stars suggests strongly that WN3/O3 stars are not the descendants of single massive stars (30 M⊙ or above). Instead, they are likely products of interacting binaries at lower initial mass (10-18 M⊙). Comparison with binary models suggests a probable origin with primaries in this mass range that were stripped of their H envelopes through non-conservative mass transfer by a low-mass secondary. We show that model spectra and positions on the Hertzsprung-Russell diagram for binary-stripped stars are consistent with WN3/O3 stars. Monitoring radial velocities with high-resolution spectra can test for low-mass companions or runaway velocities. With lower initial mass and environments that avoid very massive stars, the WN3/O3 stars fit expectations for progenitors of Type Ib and possibly Type Ibn supernovae.
SOUTHERN MASSIVE STARS AT HIGH ANGULAR RESOLUTION: OBSERVATIONAL CAMPAIGN AND COMPANION DETECTION
Sana, H.; Le Bouquin, J.-B.; Duvert, G.
Multiplicity is one of the most fundamental observable properties of massive O-type stars and offers a promising way to discriminate between massive star formation theories. Nevertheless, companions at separations between 1 and 100 milliarcsec (mas) remain mostly unknown due to intrinsic observational limitations. At a typical distance of 2 kpc, this corresponds to projected physical separations of 2-200 AU. The Southern MAssive Stars at High angular resolution survey (SMaSH+) was designed to fill this gap by providing the first systematic interferometric survey of Galactic massive stars. We observed 117 O-type stars with VLTI/PIONIER and 162 O-type stars with NACO/Sparse Aperturemore » Masking (SAM), probing the separation ranges 1-45 and 30-250 mas and brightness contrasts of ΔH < 4 and ΔH < 5, respectively. Taking advantage of NACO's field of view, we further uniformly searched for visual companions in an 8'' radius down to ΔH = 8. This paper describes observations and data analysis, reports the discovery of almost 200 new companions in the separation range from 1 mas to 8'' and presents a catalog of detections, including the first resolved measurements of over a dozen known long-period spectroscopic binaries. Excluding known runaway stars for which no companions are detected, 96 objects in our main sample (δ < 0°; H < 7.5) were observed both with PIONIER and NACO/SAM. The fraction of these stars with at least one resolved companion within 200 mas is 0.53. Accounting for known but unresolved spectroscopic or eclipsing companions, the multiplicity fraction at separation � < 8'' increases to f {sub m} = 0.91 ± 0.03. The fraction of luminosity class V stars that have a bound companion reaches 100% at 30 mas while their average number of physically connected companions within 8'' is f {sub c} = 2.2 ± 0.3. This demonstrates that massive stars form nearly exclusively in multiple systems. The nine non-thermal radio emitters observed by SMaSH+ are all resolved
Star formation and extinct radioactivities
Cameron, A. G. W.
An assessment is made of the evidence for the existence of now-extinct radioactivities in primitive solar system material, giving attention to implications for the early stages of sun and solar system formation. The characteristics of possible disturbances in dense molecular clouds which can initiate the formation of cloud cores is discussed, with emphasis on these disturbances able to generate fresh radioactivities. A one-solar mass red giant star on the asymptotic giant branch appears to have been the best candidate to account for the short-lived extinct radioactivities in the early solar system.
Wolf-Rayet stars
Abbott, David C.; Conti, Peter S.
The properties and evolutionary status of WR stars are examined, reviewing the results of recent observational and theoretical investigations. Topics discussed include spectral types and line strengths, magnitudes and colors, intrinsic variability, IR and radio observations, X-ray observations, the Galactic distribution of WR stars, WR stars in other galaxies, and WR binaries. Consideration is given to the inferred masses, composition, and stellar winds of WR stars; model atmospheres; WR stars and the Galactic environment; and WR stars as a phase of stellar evolution. Diagrams, graphs, and tables of numerical data are provided.
Enigma of Runaway Stars Solved
. In fact, this is one of the most `perfect' bow shocks of parabolic form ever observed around an OB-runaway. Moreover, the orientation of the bow shock indicates that the system is moving towards the north; its origin must therefore lie somewhere south of its present position in the sky. It also turns out that the accordingly deduced path of HD77581 crosses a well-known OB-association with the designation Vel OB1 . At the measured distance of Vel OB1 of about 6000 lightyears, the observed proper motion and radial velocity of HD77581 indicate a space velocity of 90 km/sec. With this velocity, it would have taken HD77581 and its compact companion about 2.5 million years to travel the distance between Vel OB1 and its present position. This corresponds exactly to the expected time that has passed since the supernova explosion of the progenitor star of Vela~X-1, as deduced from the observed properties of the binary system. The puzzle comes together Now everything fits! The observation of a bow shock around the OB star HD77581 and its compact companion Vela X-1 supports the scenario originally proposed by Blaauw to create OB-runaway stars by the supernova explosion of the binary companion. Following back the path of the system resulted in the discovery of the place where it was born and from where it escaped after the violent supernova explosion which produced the neutron star that now manifests itself as the strong X-ray source known as Vela X-1. More information about this research project This research project is described in ESO Preprint no.~1199 and will appear shortly as a Letter to the Editor in `Astrophysical Journal' (ApJ 475, L37-L40). Notes: [1] Professor Adriaan Blaauw is a well-known Dutch astronomer (Leiden and Groningen). He participated very actively in the build-up of ESO in the 1950's and 60's and he was ESO Director General from 1970 - 1974. He is the author of ` ESO's Early History - The European Southern Observatory from concept to reality ' (1991). [2
Have We Finally Found Pop III Stars?
Kohler, Susanna
Elusive Population: Population III stars — the theoretical generation of extremely metal-poor stars that should have been formed in the early universe before metals existed — have been conspicuously absent in observations. But a team led by David Sobral (Institute of Astrophysics and Space Sciences, University of Lisbon, and Leiden Observatory) may have changed this paradigm with their recent detection of an extremely bright galaxy in the early universe. The team's broad survey of distant galaxies using ESO's Very Large Telescope provides a glimpse of the universe as it was only 800 million years after the Big Bang. The survey uncovered several unusually bright galaxies — including the brightest galaxy ever seen at this distance, an important discovery by itself. But further scrutiny of this galaxy, named CR7, produced an even more exciting find: a bright pocket of the galaxy contained no sign of any metals. Follow-up with other telescopes confirmed this initial detection. Formation Waves: Sobral and his team postulate that we are observing this galaxy at just the right time to have caught a cluster of Population III stars — the bright, metal-free region of the galaxy — at the end of a wave of early star formation. The observations of CR7 also suggest the presence of regular stars in clumps around the metal-free pocket. These older, surrounding clusters may have formed stars first, helping to ionize a local bubble in the galaxy and allowing us to now observe the light from CR7. It was previously thought that Population III stars might only be found in small, dim galaxies, making them impossible for us to detect. But CR7 provides an interesting alternative: this galaxy is bright, and the candidate Population III stars are surrounded by clusters of normal stars. This suggests that these first-generation stars might in fact be easier to detect than was originally thought. Additional follow-up observations with other telescopes will help to confirm the
Asteroseismology of OB stars with CoRoT
Degroote, P.; Aerts, C.; Samadi, R.; Miglio, A.; Briquet, M.; Auvergne, M.; Baglin, A.; Baudin, F.; Catala, C.; Michel, E.
The CoRoT satellite is revolutionizing the photometric study of massive O-type and B-type stars. During its long runs, CoRoT observed the entire main sequence B star domain, from typical hot β Cep stars, via cooler hybrid p- and g-mode pulsators to the SPB stars near the edge of the instability strip. CoRoT lowers the sensitivity barrier from the typical mmag-precision reached from the ground, to the μmag-level reached from space. Within the wealth of detected and identified pulsation modes, relations have been found in the form of multiplets, combination of frequencies, and frequency- and period spacings. This wealth of observational evidence is finally providing strong constraints to test current models of the internal structure and pulsations of hot stars. Aside from the expected opacity driven modes with infinite lifetime, other unexpected types of variability are detected in massive stars, such as modes of stochastic nature. The simultaneous observation of all these light curve characteristics implies a challenge for both observational asteroseismology and stellar modelling. The CoRoT space mission was developed and is operated by the French space agency CNES, with participation of ESA's RSSD and Science Programmes, Austria, Belgium, Brazil, Germany, and Spain.
Evolution of massive stars in very young clusters and associations
Stothers, R. B.
Statistics concerning the stellar content of young galactic clusters and associations which show well defined main sequence turnups have been analyzed in order to derive information about stellar evolution in high-mass galaxies. The analytical approach is semiempirical and uses natural spectroscopic groups of stars on the H-R diagram together with the stars' apparent magnitudes. The new approach does not depend on absolute luminosities and requires only the most basic elements of stellar evolution theory. The following conclusions are offered on the basis of the statistical analysis: (1) O-tupe main-sequence stars evolve to a spectral type of B1 during core hydrogen burning; (2) most O-type blue stragglers are newly formed massive stars burning core hydrogen; (3) supergiants lying redward of the main-sequence turnup are burning core helium; and most Wolf-Rayet stars are burning core helium and originally had masses greater than 30-40 solar mass. The statistics of the natural spectroscopic stars in young galactic clusters and associations are given in a table.
Imaging Variable Stars with HST
Karovska, Margarita
The Hubble Space Telescope (HST) observations of astronomical sources, ranging from objects in our solar system to objects in the early Universe, have revolutionized our knowledge of the Universe its origins and contents.I will highlight results from HST observations of variable stars obtained during the past twenty or so years. Multiwavelength observations of numerous variable stars and stellar systems were obtained using the superb HST imaging capabilities and its unprecedented angular resolution, especially in the UV and optical. The HST provided the first detailed images probing the structure of variable stars including their atmospheres and circumstellar environments. AAVSO observations and light curves have been critical for scheduling of many of these observations and provided important information and context for understanding of the imaging results of many variable sources. I will describe the scientific results from the imaging observations of variable stars including AGBs, Miras, Cepheids, semi-regular variables (including supergiants and giants), YSOs and interacting stellar systems with a variable stellar components. These results have led to an unprecedented understanding of the spatial and temporal characteristics of these objects and their place in the stellar evolutionary chains, and in the larger context of the dynamic evolving Universe.
Karovska, M.
(Abstract only) The Hubble Space Telescope (HST) observations of astronomical sources, ranging from objects in our solar system to objects in the early Universe, have revolutionized our knowledge of the Universe its origins and contents. I highlight results from HST observations of variable stars obtained during the past twenty or so years. Multiwavelength observations of numerous variable stars and stellar systems were obtained using the superb HST imaging capabilities and its unprecedented angular resolution, especially in the UV and optical. The HST provided the first detailed images probing the structure of variable stars including their atmospheres and circumstellar environments. AAVSO observations and light curves have been critical for scheduling of many of these observations and provided important information and context for understanding of the imaging results of many variable sources. I describe the scientific results from the imaging observations of variable stars including AGBs, Miras, Cepheids, semiregular variables (including supergiants and giants), YSOs and interacting stellar systems with a variable stellar components. These results have led to an unprecedented understanding of the spatial and temporal characteristics of these objects and their place in the stellar evolutionary chains, and in the larger context of the dynamic evolving Universe.
White Dwarf Stars
Peering deep inside a cluster of several hundred thousand stars, NASA Hubble Space Telescope has uncovered the oldest burned-out stars in our Milky Way Galaxy, giving astronomers a fresh reading on the age of the universe.
Assembly Line of Stars
This image from NASA Herschel, in the constellation of Vulpecula, shows an entire assembly line of newborn stars. The diffuse glow reveals the widespread cold reservoir of raw material that our Milky Way galaxy has in stock for building stars.
Star formation: Cosmic feast
Scaringi, Simone
Low-mass stars form through a process known as disk accretion, eating up material that orbits in a disk around them. It turns out that the same mechanism also describes the formation of more massive stars.
Massive Star Makes Waves
The giant star Zeta Ophiuchi, a young, large and hot star located around 370 light-years away, is having a hocking effect on the surrounding dust clouds in this infrared image from NASA Spitzer Space Telescope.
Sloshing Star Goes Supernova
NuSTAR has provided the first observational evidence in support of a theory that says exploding stars slosh around before detonating. That theory, referred to as mild asymmetries, is shown here in a simulation by Christian Ott.
AgSTAR Accomplishments
Showcases AgSTAR's accomplishments reducing greenhouse gas emissions in the agriculture sector. Through outreach, education, training, and other tools, AgSTAR continues to help evaluate, construct, and maintain anaerobic digesters on livestock farms.
Star Formation in Galaxies
Topics addressed include: star formation; galactic infrared emission; molecular clouds; OB star luminosity; dust grains; IRAS observations; galactic disks; stellar formation in Magellanic clouds; irregular galaxies; spiral galaxies; starbursts; morphology of galactic centers; and far-infrared observations.
Intrinsically variable stars
Bohm-Vitense, Erika; Querci, Monique
The characteristics of intrinsically variable stars are examined, reviewing the results of observations obtained with the IUE satellite since its launch in 1978. Selected data on both medium-spectral-class pulsating stars (Delta Cep stars, W Vir stars, and related groups) and late-type variables (M, S, and C giants and supergiants) are presented in spectra, graphs, and tables and described in detail. Topics addressed include the calibration of the the period-luminosity relation, Cepheid distance determination, checking stellar evolution theory by the giant companions of Cepheids, Cepheid masses, the importance of the hydrogen convection zone in Cepheids, temperature and abundance estimates for Population II pulsating stars, mass loss in Population II Cepheids, SWP and LWP images of cold giants and supergiants, temporal variations in the UV lines of cold stars, C-rich cold stars, and cold stars with highly ionized emission lines.
Another Death Star?
Although Mimas holds the unofficial designation of Death Star moon, Tethys is seen here also vaguely resembling the space station from Star Wars. Apparently, Tethys doesnt want Mimas to have all the fun!
X-Ray Emission from Massive Stars in Cyg OB2
Rauw, G.; Nazé, Y.; Wright, N. J.; Drake, J. J.; Guarcello, M. G.; Prinja, R. K.; Peck, L. W.; Albacete Colombo, J. F.; Herrero, A.; Kobulnicky, H. A.; Sciortino, S.; Vink, J. S.
We report on the analysis of the Chandra-ACIS data of O, B, and WR stars in the young association Cyg OB2. X-ray spectra of 49 O-stars, 54 B-stars, and 3 WR-stars are analyzed and for the brighter sources, the epoch dependence of the X-ray fluxes is investigated. The O-stars in Cyg OB2 follow a well-defined scaling relation between their X-ray and bolometric luminosities: {log}\\\\frac{{L}{{X}}}{{L}{bol}}=-7.2+/- 0.2. This relation is in excellent agreement with the one previously derived for the Carina OB1 association. Except for the brightest O-star binaries, there is no general X-ray overluminosity due to colliding winds in O-star binaries. Roughly half of the known B-stars in the surveyed field are detected, but they fail to display a clear relationship between LX and Lbol. Out of the three WR stars in Cyg OB2, probably only WR 144 is itself responsible for the observed level of X-ray emission, at a very low {log}\\\\frac{{L}{{X}}}{{L}{bol}}=-8.8+/- 0.2. The X-ray emission of the other two WR-stars (WR 145 and 146) is most probably due to their O-type companion along with a moderate contribution from a wind-wind interaction zone.
Observing metal-poor stars with X-Shooter
Caffau, E.; Bonifacio, P.; Sbordone, L.; Monaco, L.; François; , P.
The extremely metal-poor stars (EMP) hold in their atmospheres the fossil record of the chemical composition of the early phases of the Galactic evolution. The chemical analysis of such objects provides important constraints on these early phases. EMP stars are very rare objects; to dig them out large amounts of data have to be considered. With an automatic procedure, we analysed objects with colours of Turn-Off stars from the Sloan Digital Sky Survey to select a sample of good candidate EMP stars. During the French-Italian GTO of the spectrograph X-Shooter, we observed a sample of these candidates. We could confirm the low metallicity of our sample of stars, and we succeeded in finding a record metal-poor star.
Wolf-Rayet stars in the Small Magellanic Cloud as testbed for massive star evolution
Schootemeijer, A.; Langer, N.
Context. The majority of the Wolf-Rayet (WR) stars represent the stripped cores of evolved massive stars who lost most of their hydrogen envelope. Wind stripping in single stars is expected to be inefficient in producing WR stars in metal-poor environments such as the Small Magellanic Cloud (SMC). While binary interaction can also produce WR stars at low metallicity, it is puzzling that the fraction of WR binaries appears to be about 40%, independent of the metallicity. Aim. We aim to use the recently determined physical properties of the twelve known SMC WR stars to explore their possible formation channels through comparisons with stellar models. Methods: We used the MESA stellar evolution code to construct two grids of stellar models with SMC metallicity. One of these consists of models of rapidly rotating single stars, which evolve in part or completely chemically homogeneously. In a second grid, we analyzed core helium burning stellar models assuming constant hydrogen and helium gradients in their envelopes. Results: We find that chemically homogeneous evolution is not able to account for the majority of the WR stars in the SMC. However, in particular the apparently single WR star SMC AB12, and the double WR system SMC AB5 (HD 5980) appear consistent with this channel. We further find a dichotomy in the envelope hydrogen gradients required to explain the observed temperatures of the SMC WR stars. Shallow gradients are found for the WR stars with O star companions, while much steeper hydrogen gradients are required to understand the group of hot apparently single WR stars. Conclusions: The derived shallow hydrogen gradients in the WR component of the WR+O star binaries are consistent with predictions from binary models where mass transfer occurs early, in agreement with their binary properties. Since the hydrogen profiles in evolutionary models of massive stars become steeper with time after the main sequence, we conclude that most of the hot (Teff > 60 k
Dibaryons in neutron stars
Olinto, Angela V.; Haensel, Pawel; Frieman, Joshua A.
The effects are studied of H-dibaryons on the structure of neutron stars. It was found that H particles could be present in neutron stars for a wide range of dibaryon masses. The appearance of dibaryons softens the equations of state, lowers the maximum neutron star mass, and affects the transport properties of dense matter. The parameter space is constrained for dibaryons by requiring that a 1.44 solar mass neutron star be gravitationally stable.
Chromospheres of Coronal Stars
Linsky, Jeffrey L.; Wood, Brian E.
We summarize the main results obtained from the analysis of ultraviolet emission line profiles of coronal late-type stars observed with the Goddard High Resolution Spectrograph (GHRS) on the Hubble Space Telescope. The excellent GHRS spectra provide new information on magnetohydrodynamic phenomena in the chromospheres and transition regions of these stars. One exciting new result is the discovery of broad components in the transition region lines of active stars that we believe provide evidence for microflare heating in these stars.
Stars Spring up Out of the Darkness
[figure removed for brevity, see original site] Click on the image for movie of Stars Spring up Out of the Darkness
This artist's animation illustrates the universe's early years, from its explosive formation to its dark ages to its first stars and mini-galaxies.
Scientists using NASA's Spitzer Space Telescope found patches of infrared light splattered across the sky that might be the collective glow of clumps of the universe's first objects. Astronomers do not know if these first objects were stars or 'quasars,' which are black holes voraciously consuming surrounding gas.
The movie begins with a flash of color that represents the birth of the universe, an explosion called the Big Bang that occurred about 13.7 billion years ago. A period of darkness ensues, where gas begins to clump together.
The universe's first stars are then shown springing up out of the gas clumps, flooding the universe with light, an event that probably happened about a few hundred million years after the Big Bang. Though these first stars formed out of gas alone, their deaths seeded the universe with the dusty heavy chemical elements that helped create future generations of stars.
The first stars, called Population III stars (our star is a Population I star), were much bigger and brighter than any in our nearby universe, with masses about 1,000 times that of our sun. They grouped together into mini-galaxies, which then merged to form galaxies like our own mature Milky Way galaxy.
The first quasars, not shown here, ultimately became the centers of powerful galaxies that are more common in the distant universe.
America's Star Libraries
Lyons, Ray; Lance, Keith Curry
"Library Journal"'s new national rating of public libraries, the "LJ" Index of Public Library Service, identifies 256 "star" libraries. It rates 7,115 public libraries. The top libraries in each group get five, four, or three Michelin guide-like stars. All included libraries, stars or not, can use their scores to learn from their peers and improve…
Seeing Stars in Serpens
Infant stars are glowing gloriously in this image of the Serpens star-forming region, captured by NASA Spitzer Space Telescope. The reddish-pink dots are baby stars deeply embedded in the cosmic cloud of gas and dust that collapsed to create it.
Magnetized anisotropic stars
Stelea, Cristian; Dariescu, Marina-Aura; Dariescu, Ciprian
We extend a known solution-generating technique for isotropic fluids in order to construct more general models of anisotropic stars with poloidal magnetic fields. In particular, we discuss the magnetized versions of some well-known exact solutions describing anisotropic stars and dark energy stars, and we describe some of their properties.
Managing the star performer.
Hills, Laura
Our culture seems to be endlessly fascinated with its stars in entertainment, athletics, politics, and business, and holds fast to the idea that extraordinary talent accounts for an individual's extraordinary performance. At first glance, managing a star performer in your medical practice may seem like it would be an easy task. However, there's much more to managing a star performer than many practice managers realize. The concern is how to keep the star performer happy and functioning at a high level without detriment to the rest of the medical practice team. This article offers tips for practice managers who manage star performers. It explores ways to keep the star performer motivated, while at the same time helping the star performer to meld into the existing medical practice team. This article suggests strategies for redefining the star performer's role, for holding the star performer accountable for his or her behavior, and for coaching the star performer. Finally, this article offers practical tips for keeping the star performer during trying times, for identifying and cultivating new star performers, and for managing medical practice prima donnas.
The IACOB project . III. New observational clues to understand macroturbulent broadening in massive O- and B-type stars
Simón-Díaz, S.; Godart, M.; Castro, N.; Herrero, A.; Aerts, C.; Puls, J.; Telting, J.; Grassitelli, L.
late-B dwarfs and giants, which present a mixture of cases in terms of line-profile shape and variability, the whole O-type and B supergiant domain (or, roughly speaking, stars with MZAMS ≳ 15 M⊙) is fully dominated by stars with a remarkable non-rotational broadening component and very similar profiles (including type of variability). We provide some examples illustrating how this observational dataset can be used to evaluate scenarios aimed at explaining the existence of sources of non-rotational broadening in massive stars. Full Table 1 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/597/A22
VizieR Online Data Catalog: VLT-FLAMES Tarantula Survey. 30 Dor luminous stars (Doran+, 2013)
Doran, E. I.; Crowther, P. A.; de Koter, A.; Evans, C. J.; McEvoy, C.; Walborn, N. R.; Bastian, N.; Bestenlehner, J. M.; Grafener, G.; Herrero, A.; Kohler, K.; Maiz Apellaniz, J.; Najarro, F.; Puls, J.; Sana, H.; Schneider, F. R. N.; Taylor, W. D.; van Loon, J. T.; Vink, J. S.
A census was compiled of all the hot luminous stars within the central 10 arcminutes of 30 Doradus. Candidate hot luminous stars were selected from a series of photometric catalogues, using a set of criteria explained in the paper. All stars meeting this photometric criteria are listed in Tabled1.dat. In addition, Table D1 includes all known Wolf-Rayet and Of/WN stars in the region, which may not have been selected due to photometric effects. Spectral Types were then matched to as many of the candidate stars in Tabled1.dat as possible. Stellar parameters were determined for all stars with the following spectral types: W-R, Of/WN, O-type, B-supergiant, B-giant B1I or earlier, B-dwarf, B0.5V or earlier. These parameters are listed in Tabled2.dat. Parameters of all O-type and B-type stars were derived through various calibrations. Parameters of W-R and Of/WN stars were based on previous work or various template models explained in the paper. (2 data files).
Induced Star Formation
Kennicutt, Robert C., Jr.
Overview: Induced Star Formation and Interactions Introduction Historical Background: First Hints Systematic Studies: Starbursts Interactions and Nuclear activity IRAS and Ultralumious starburst Galaxies The 1990's: HST, Supercomputers, and the Distant Universe Key Questions and Issues Organization of Lectures Star Formation Properties of Normal Galaxies Observational Techniques Results: Star Formation in Normal Galaxies Interpretation: Star Formation Histories Global Star Formation in interacting Galaxies A Gallery of Interactions and Mergers Star Formation Statistics: Guilt By Association Tests SFRs in Interacting vs Noninteracting Galaxies Kinematic Properties and Regulation of SFRs Induced Nuclear Activity and Star Formation Background: Nuclear Spectra and Classification Nuclear Star Formation and Starbursts Nuclear Star Formation and Interactions Induced AGN Activity: Statistics of Seyfert Galaxies Environments of Quasars Kinematic Clues to the Triggering of AGNs Infrared Luminous Galaxies and Starbursts Background: IR Luminous Galaxies and IRAS Infrared Luminosity Function and Spectra Infrared Structure and Morphology Interstellar Gas X-Ray Emission and Superwinds Optical, UV, and Near-Infrared Spectra Radio Continuum Emission Evidence for Interactions and Mergers The Power Source: Starbursts or Dusty AGNs? Spectral Diagnostics of Starbursts Evolutionary Synthesis Models Applications: Integrated Colors of Interacting Galaxies Applications: Hα Emission, Colors, and SFRs Applications: Spectral Modelling of Evolved Starbursts Infrared Starbursts and the IMF in starbursts Triggering and Regulation of Star Formation: The Problem Introduction: Star Formation as a Nonlinear Process The schmidt Law in Normal Galaxies Star Formation Regimes in Interacting Galaxies Summary Triggering and Regulation of Starbusts: Theoretical Ideas Gravitational Star Formation Thresholds Cloud Collision Models Radial Transport of Gas: Clues from Barred Galaxies Simulations of Starbursts
The most luminous stars.
Humphreys, R M; Davidson, K
Stars with individual luminosities more than a million times that of the sun are now being studied in a variety of contexts. Observational and theoretical ideas about the most luminous stars have changed greatly in the past few years. They can be observed spectroscopically even in nearby galaxies. They are not very stable; some have had violent outbursts in which large amounts of mass were lost. Because of their instabilities, these stars do not evolve to become red superglants as less luminous stars do. Theoretical scenarios for the evolution of these most massive stars depend on the effects of turbulence and mixing combined with high radition densities.
The TAROT Suspected Variable Star Catalog
Damerdji, Y.; Klotz, A.; Boër, M.
TAROT (Télescope à Action Rapide pour les Objets Transitoires) is a robotic observatory designed to observe very early optical transients of gamma-ray bursts (GRBs). As GRBs do not often occur, we use TAROT for various other celestial targets spread over the sky. For every field observed by TAROT, we computed the magnitudes of every star. From this work, we found 1175 new variable stars brighter than 17 mag. We selected the best variable star candidates and compiled them in the TSVSC1 (TAROT Suspected Variable Star Catalog, ver. 1), which also contains Fourier-series coefficients that fit the light curves. Based on observations collected with the TAROT instrument at the Calern Observatory, France. Complementary observations were carried out with the T80 telescope at the Observatoire de Haute-Provence, France. Additional material described in § 5 is available in electronic format at the CDS at http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/AJ/.
Evolved massive stars in W33 and in GMC 23.3-0.3
Messineo, Maria; Clark, J. Simon; Figer, Donald F.; Menten, Karl M.; Kudritzki, Rolf-Peter; Najarro, Francisco; Rich, Michael; Ivanov, Valentin D.; Valenti, Elena; Trombley, Christine; Chen, Rosie; Davies, Ben; MacKenty, John W.
We have conducted an infrared spectroscopic survey for massive evolved stars and/or clusters in the Galactic giant molecular clouds G23.3-0.3 and W33. A large number of extraordinary sub-clumps/clusters of massive stars were detected. The spatial and temporal distribution of these massive stars yields information on the star formation history of the clouds.In G23.3-0.3, we discovered a dozen massive O-type stars, one candidate luminous blue variable, and several red supergiants. The O-type stars have masses from 25 to 50 Msun and ages of 5-8 Myr, while the RSGs belong to a burst that occurred 20-30 Myr ago. Therefore, GMC G23.3-0.3 has had one of the longest known histories of star formation (20-30 Myr). GMC G23.3-0.3 is rich in HII regions and supernova remnants; we detected massive stars in the cores of SNR W41 and of SNR G22.7-0.2.In W33, we detected a few evolved O-type stars and one Wolf-Rayet star, but none of the late-type objects has the luminosity of a red supergiant. W33 is characterized by discrete sources and has had at least 3-5 Myr of star formation history, which is now propagating from west to east. While our detections of massive evolved stars in W33 are made on the west side of the cloud, several dense molecular cores that may harbor proto clusters have recently been detected on the east side of the cloud by Immer et al. (2014).Messineo, Maria; Menten, Karl M.; Figer, Donald F.; Davies, Ben; Clark, J. Simon; Ivanov, Valentin D.Kudritzki, Rolf-Peter; Rich, R. Michael; MacKenty, John W.; Trombley, Christine 2014A&A...569A..20MMessineo, Maria; Clark, J. Simon; Figer, Donald F.; Kudritzki, Rolf-Peter; Francisco, Najarro; Rich, R. Michael; Menten, Karl M.; Ivanov, Valentin D.; Valenti, Elena; Trombley, Christine; Chen, C.H. Rosie; Davies, Ben; submitted to ApJ.
Ponderable soliton stars
The theory of Lee and Pang (1987), who obtained solutions for soliton stars composed of zero-temperature fermions and bosons, is applied here to quark soliton stars. Model soliton stars based on a simple physical model of the proton are computed, and the properties of the solitons are discussed, including the important problem of the existence of a limiting mass and thus the possible formation of black holes of primordial origin. It is shown that there is a definite mass limit for ponderable soliton stars, so that during cooling a soliton star might reach a stage beyond which no equilibrium configuration exists and the soliton star probably will collapse to become a black hole. The radiation of ponderable soliton stars may alter the short-wavelength character of the cosmic background radiation, and may be observed as highly redshifted objects at z of about 100,000.
Spectrophotometry of Symbiotic Stars
Boyd, David
Symbiotic stars are fascinating objects - complex binary systems comprising a cool red giant star and a small hot object, often a white dwarf, both embedded in a nebula formed by a wind from the giant star. UV radiation from the hot star ionises the nebula producing a range of emission lines. These objects have composite spectra with contributions from both stars plus the nebula and these spectra can change on many timescales. Being moderately bright, they lend themselves well to amateur spectroscopy. This paper describes the symbiotic star phenomenon, shows how spectrophotometry can be used to extract astrophysically useful information about the nature of these systems, and gives results for three symbiotic stars based on the author's observations.
Stars Too Old to be Trusted?
Analysing a set of stars in a globular cluster with ESO's Very Large Telescope, astronomers may have found the solution to a critical cosmological and stellar riddle. Until now, an embarrassing question was why the abundance of lithium produced in the Big Bang is a factor 2 to 3 times higher than the value measured in the atmospheres of old stars. The answer, the researchers say, lies in the fact that the abundances of elements measured in a star's atmosphere decrease with time. ESO PR Photo 30/06 ESO PR Photo 30/06 Globular cluster NGC 6397, with some of the FLAMES-UVES target stars highlighted "Such trends are predicted by models that take into account the diffusion of elements in a star", said Andreas Korn, lead-author of the paper reporting the results in this week's issue of the journal Nature [1,2]. "But an observational confirmation was lacking. That is, until now." Lithium is one of the very few elements to have been produced in the Big Bang. Once astronomers know the amount of ordinary matter present in the Universe [3], it is rather straightforward to derive how much lithium was created in the early Universe. Lithium can also be measured in the oldest, metal-poor stars, which formed from matter similar to the primordial material. But the cosmologically predicted value is too high to reconcile with the measurements made in the stars. Something is wrong, but what? Diffusive processes altering the relative abundances of elements in stars are well known to play a role in certain classes of stars. Under the force of gravity, heavy elements will tend to sink out of visibility into the star over the course of billions of years. "The effects of diffusion are expected to be more pronounced in old, very metal-poor stars", said Korn. "Given their greater age, diffusion has had more time to produce sizeable effects than in younger stars like the Sun." The astronomers thus set up an observational campaign to test these model predictions, studying a variety of stars in
Hayashi and the thermal physics of star-forming clouds
Larson, Richard B.
This brief historical review highlights the early work of Hayashi and his associates on the thermal physics of star-forming clouds, as summarized in the temperature-density diagrams first presented by this group. Some of the more recent developments in this subject, including its application to understanding stellar masses and to understanding the formation of the first stars, are also briefly reviewed.
The High Angular Resolution Multiplicity of Massive Stars
binaries: visual – stars: early-type – stars: individual ( iota Ori, delta Ori, delta Sco) – techniques: interferometric Online-only material...STATEMENT Approved for public release; distribution unlimited 13. SUPPLEMENTARY NOTES 14. ABSTRACT 15. SUBJECT TERMS 16. SECURITY
The Gaia-ESO Survey and CSI 2264: Substructures, disks, and sequential star formation in the young open cluster NGC 2264
Venuti, L.; Prisinzano, L.; Sacco, G. G.; Flaccomio, E.; Bonito, R.; Damiani, F.; Micela, G.; Guarcello, M. G.; Randich, S.; Stauffer, J. R.; Cody, A. M.; Jeffries, R. D.; Alencar, S. H. P.; Alfaro, E. J.; Lanzafame, A. C.; Pancino, E.; Bayo, A.; Carraro, G.; Costado, M. T.; Frasca, A.; Jofré, P.; Morbidelli, L.; Sousa, S. G.; Zaggia, S.
Context. Reconstructing the structure and history of young clusters is pivotal to understanding the mechanisms and timescales of early stellar evolution and planet formation. Recent studies suggest that star clusters often exhibit a hierarchical structure, possibly resulting from several star formation episodes occurring sequentially rather than a monolithic cloud collapse. Aims: We aim to explore the structure of the open cluster and star-forming region NGC 2264 ( 3 Myr), which is one of the youngest, richest and most accessible star clusters in the local spiral arm of our Galaxy; we link the spatial distribution of cluster members to other stellar properties such as age and evolutionary stage to probe the star formation history within the region. Methods: We combined spectroscopic data obtained as part of the Gaia-ESO Survey (GES) with multi-wavelength photometric data from the Coordinated Synoptic Investigation of NGC 2264 (CSI 2264) campaign. We examined a sample of 655 cluster members, with masses between 0.2 and 1.8 M⊙ and including both disk-bearing and disk-free young stars. We used Teff estimates from GES and g,r,i photometry from CSI 2264 to derive individual extinction and stellar parameters. Results: We find a significant age spread of 4-5 Myr among cluster members. Disk-bearing objects are statistically associated with younger isochronal ages than disk-free sources. The cluster has a hierarchical structure, with two main blocks along its latitudinal extension. The northern half develops around the O-type binary star S Mon; the southern half, close to the tip of the Cone Nebula, contains the most embedded regions of NGC 2264, populated mainly by objects with disks and ongoing accretion. The median ages of objects at different locations within the cluster, and the spatial distribution of disked and non-disked sources, suggest that star formation began in the north of the cluster, over 5 Myr ago, and was ignited in its southern region a few Myr later
On the origin of high-velocity runaway stars
We explore the hypothesis that some high-velocity runaway stars attain their peculiar velocities in the course of exchange encounters between hard massive binaries and a very massive star (either an ordinary 50-100Msolar star or a more massive one, formed through runaway mergers of ordinary stars in the core of a young massive star cluster). In this process, one of the binary components becomes gravitationally bound to the very massive star, while the second one is ejected, sometimes with a high speed. We performed three-body scattering experiments and found that early B-type stars (the progenitors of the majority of neutron stars) can be ejected with velocities of >~200-400kms-1 (typical of pulsars), while 3-4Msolar stars can attain velocities of >~300-400kms-1 (typical of the bound population of halo late B-type stars). We also found that the ejected stars can occasionally attain velocities exceeding the Milky Ways's escape velocity.
Debris Disks Among the Shell Stars: Insights from Spitzer
Roberge, Aki; Weinberger, Alycia; Teske, Johanna
Shell stars are a class of early-type stars that show narrow absorption lines in their spectra that appear to arise from circumstellar class. This observationally defined class contains a variety of objects, including evolved stars and classical Be stars. However, some of the main sequence shell stars harbor debris disks and younger protoplanetary disks, though this aspect of the class has been largely overlooked. We surveyed a set of main sequence stars for cool dust using Spitzer MIPS and found four additional systems with IR excesses at both 24 and 70 microns. This indicates that the stars have both circumstellar gas and dust, and are likely to be edge-on debris disks. Our estimate of the disk fraction among nearby main sequence shell stars is 48% +/- 14%. We discuss here the nature of the shell stars and present preliminary results from ground-based optical spectra of the survey target stars. We will also outline our planned studies aimed at further characterization of the shell star class.
Spectropolarimetry of Post-AGB Stars
Trammell, S. R.; Goodrich, R. W.; Dinerstein, H. L.
We have used the technique of optical spectropolarimetry to investigate post-AGB stars, objects that represent the first stages of the transition from the AGB to a planetary nebula. Several of the observed objects display unpolarized emission lines superimposed on a highly polarized continuum. The continuum polarization provides evidence for the presence of an aspherical dust envelope early in the transition process. The observed objects were chosen from several samples: high latitude supergiants with IR excesses that are thought to be post-AGB stars (e.g. Bond et. al. 1984, PASP, 96, 176), their lower latitude counterparts (e.g. Hrivnak et. al. 1989, ApJ, 346, 265), post-AGB stars shown by Johnson & Jones (1991, AJ, 101, 1735) to have high broad band polarizations, and three highly polarized extreme carbon stars investigated by Cohen & Schmidt (1982, ApJ, 259, 693). GL 1403, an extreme carbon star, shows an abrupt position angle rotation at 6000 Angstroms, implying that at blue wavelengths we see a scattered stellar continuum, while the star itself is hidden from direct view. Longward of the position angle rotation, we begin to see the star directly. Menzies & Whitelock (1988, MNRAS, 233, 697) proposed that IRAS 20056+1834, an unreddened GO supergiant with very strong Na I emission lines and a large infrared excess, is a mass-losing star obscured from direct view, in which the photospheric light is seen in reflection. Our data support this interpretation; the Na I emission is unpolarized, indicating that it is produced in the shell, while the continuum is scattered and polarized (5-7%) by the aspherical shell of material. IRAS 20000+3239 also shows unpolarized Na I D emission and is probably similar to IRAS 20056+1834. IRC +10420 exhibits unpolarized Hα emission and GL 2699, an extreme carbon star, displays both polarized and unpolarized Hα as well as unpolarized low excitation forbidden [S II] and [O I] emission lines.
Kepler's first view of O-star variability: K2 data of five O stars in Campaign 0 as a proof of concept for O-star asteroseismology
Buysschaert, B.; Aerts, C.; Bloemen, S.; Debosscher, J.; Neiner, C.; Briquet, M.; Vos, J.; Pápics, P. I.; Manick, R.; Schmid, V. S.; Van Winckel, H.; Tkachenko, A.
We present high-precision photometric light curves of five O-type stars observed with the refurbished Kepler satellite during its Campaign 0. For one of the stars, we also assembled high-resolution ground-based spectroscopy with the HERMES spectrograph attached to the 1.2 m Mercator telescope. The stars EPIC 202060097 (O9.5V) and EPIC 202060098 (O7V) exhibit monoperiodic variability due to rotational modulation with an amplitude of 5.6 and 9.3 mmag and a rotation period of 2.63 and 5.03 d, respectively. EPIC 202060091 (O9V) and EPIC 202060093 (O9V:pe) reveal variability at low frequency but the cause is unclear. EPIC 202060092 (O9V:p) is discovered to be a spectroscopic binary with at least one multiperiodic β Cep-type pulsator whose detected mode frequencies occur in the range [0.11, 6.99] d-1 and have amplitudes between 0.8 and 2.0 mmag. Its pulsation spectrum is shown to be fully compatible with the ones predicted by core-hydrogen burning O-star models. Despite the short duration of some 33 d and the limited data quality with a precision near 100 μmag of these first K2 data, the diversity of possible causes for O-star variability already revealed from campaigns of similar duration by the MOST and CoRoT satellites is confirmed with Kepler. We provide an overview of O-star space photometry and give arguments why future K2 monitoring during Campaigns 11 and 13 at short cadence, accompanied by time-resolved high-precision high-resolution spectroscopy, opens up the possibility of in-depth O-star seismology.
WR and LBV stars
Kochiashvili, Nino; Beradze, Sophie; Kochiashvili, Ia; Natsvlishvili, Rezo; Vardosanidze, Manana
Evolutionary scenarios of massive stars were revised in recent decades, after finding "unusual", blue progenitor of SN 1987A and after detecting the more massive stars than the accepted 120 M ⊙ maximum limit of stellar masses. A very important relation exists between WR and LBV stars. They represent the earlier, pre-SN evolutionary states of massive stars. WR and LBV stars and "classic" evolutionary scheme of the relation between the different type massive stars are discussed in this article. There also exist the newest evolutionary scenarios for low metallicity massive stars, which give us a different picture of their post main-sequence evolution. There is a rather good tradition of observations and investigations of massive stars at Abastumani Astrophysical Observatory. The authors discuss the new findings on the fate of P Cygni, the LBV star. These results on the reddening of the star and about its next possible outburst in the near future were obtained on the basis of UBV long-term electrophotometric observations of P Cygni by Eugene Kharadze and Nino Magalashvili. The observations were held in 1951-1983 at Abastumani Observatory using 33-cm and 48-cm reflectors.
Star Clusters within FIRE
Perez, Adrianna; Moreno, Jorge; Naiman, Jill; Ramirez-Ruiz, Enrico; Hopkins, Philip F.
In this work, we analyze the environments surrounding star clusters of simulated merging galaxies. Our framework employs Feedback In Realistic Environments (FIRE) model (Hopkins et al., 2014). The FIRE project is a high resolution cosmological simulation that resolves star forming regions and incorporates stellar feedback in a physically realistic way. The project focuses on analyzing the properties of the star clusters formed in merging galaxies. The locations of these star clusters are identified with astrodendro.py, a publicly available dendrogram algorithm. Once star cluster properties are extracted, they will be used to create a sub-grid (smaller than the resolution scale of FIRE) of gas confinement in these clusters. Then, we can examine how the star clusters interact with these available gas reservoirs (either by accreting this mass or blowing it out via feedback), which will determine many properties of the cluster (star formation history, compact object accretion, etc). These simulations will further our understanding of star formation within stellar clusters during galaxy evolution. In the future, we aim to enhance sub-grid prescriptions for feedback specific to processes within star clusters; such as, interaction with stellar winds and gas accretion onto black holes and neutron stars.
Miras among C stars
Battinelli, P.; Demers, S.
Context. Carbon stars are among the brightest intermediate-age stars. They are seen in nearly all galaxies of the Local Group. In the Milky Way they are members of the thin disk but over a hundred have been identified in the Galactic halo. Since the halo consists essentially of an old stellar population, these carbon stars warrant special attention. We believe that such stars are trespassers and belong to streams left over by disrupted dwarf spheroidal galaxies. Aims: By performing photometric monitoring we intend to identify Miras among the halo carbon stars. Methods: We obtained, over several semesters, K and J images centered on the carbon stars in order to determine their variation and periodicity. Results: We establish the variability for a number of stars and identify the Miras among them. We collect data from the literature on the Miras among various carbon star populations and show that the fraction of Miras among carbon stars is fairly constant. We demonstrate that such fractions for the halo and Sagittarius are biased because of the way targets are selected. We finally investigate the near-infrared color distribution of Miras and carbon stars. Based on observations made with the REM Telescope, INAF Chile.The observed K and J magnitudes are available only at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/568/A100
MOST detects corotating bright spots on the mid-O-type giant ξ Persei
Ramiaramanantsoa, Tahina; Moffat, Anthony F. J.; Chené, André-Nicolas; Richardson, Noel D.; Henrichs, Huib F.; Desforges, Sébastien; Antoci, Victoria; Rowe, Jason F.; Matthews, Jaymie M.; Kuschnig, Rainer; Weiss, Werner W.; Sasselov, Dimitar; Rucinski, Slavek M.; Guenther, David B.
We have used the MOST (Microvariability and Oscillations of STars) microsatellite to obtain four weeks of contiguous high-precision broad-band visual photometry of the O7.5III(n)((f)) star ξ Persei in 2011 November. This star is well known from previous work to show prominent DACs (discrete absorption components) on time-scales of about 2 d from UV spectroscopy and non-radial pulsation with one (l = 3) p-mode oscillation with a period of 3.5 h from optical spectroscopy. Our MOST-orbit (101.4 min) binned photometry fails to reveal any periodic light variations above the 0.1 mmag 3σ noise level for periods of a few hours, while several prominent Fourier peaks emerge at the 1 mmag level in the two-day period range. These longer period variations are unlikely due to pulsations, including gravity modes. From our simulations based upon a simple spot model, we deduce that we are seeing the photometric modulation of several corotating bright spots on the stellar surface. In our model, the starting times (random) and lifetimes (up to several rotations) vary from one spot to another yet all spots rotate at the same period of 4.18 d, the best-estimated rotation period of the star. This is the first convincing reported case of corotating bright spots on an O star, with important implications for drivers of the DACs (resulting from corotating interaction regions) with possible bright-spot generation via a breakout at the surface of a global magnetic field generated by a subsurface convection zone.
Stars Spring up Out of the Darkness Artist Concept
This artist animation illustrates the universe early years, from its explosive formation to its dark ages to its first stars and mini-galaxies. Scientists using NASA Spitzer Space Telescope found patches of infrared light splattered across the sky.
Tomographic separation of composite spectra. The components of Plaskett's Star
Bagnuolo, William G., Jr.; Gies, Douglas R.; Wiggs, Michael S.
The UV photospheric lines of Plaskett's Star (HD 47129), a 14.4 day period, double lined O-type spectroscopic binary were analyzed. Archival data from IUE (17 spectra well distributed in orbital phase) were analyzed with several techniques. A cross correlation analysis, which showed that the secondary produces significant lines in the UV, indicates that the mass ratio is q = 1.18 + or - 0.12 (secondary slightly more massive). A tomography algorithm was used to produce the separate spectra of the two stars in six spectral regions. The interpolated spectral classifications of the primary and secondary, 07.3 I and 06.2 I, respectively, were estimated through a comparison of UV line ratios with those in spectral standard stars. The intensity ratio of the stars in the UV is 0.53 + or - 0.05 (primary brighter). The secondary lines appear rotationally broadened, and the projected rotational velocity V sin i for this star is estimated to be 310 + or - 20 km/s. The possible evolutionary history of this system is discussed through a comparison of the positions of the components and evolutionary tracks in the H-R diagram.
Young stars of low mass in the Gum nebula
Graham, J. A.; Heyer, Mark H.
Observations are presented for four recently formed stars in the vicinity of the Gum nebula which are heavily obscured by surrounding dust and are associated with small reflection nebulae. HH46 is the only currently active star of the sample, and it is found to have a spectral type in the range of late G-early K, with superimposed emission lines of H-alpha, Ca II, Fe I, Fe II, and weak He I at near zero velocities. It is suggested that the observed scenario of low-mass stars in an older massive star environment may be analogous to the circumstances surrounding the birth of the sun.
On the origin of the hypervelocity runaway star HD 271791
Gvaramadze, V. V.
We discuss the origin of the early-B-type runaway star HD 271791 and show that its extremely high velocity (≃530 - 920km s-1) cannot be explained within the framework of the binary-supernova ejection scenario. Instead, we suggest that HD 271791 attained its peculiar velocity in the course of a strong dynamical encounter between two hard, massive binaries or through an exchange encounter between a hard, massive binary and a very massive star, formed through runaway mergers of ordinary massive stars in the dense core of a young massive star cluster.
The energetic ion signature of an O-type neutral line in the geomagnetic tail
Martin, R. F., Jr.; Johnson, D. F.; Speiser, T. W.
An energetic ion signature is presented which has the potential for remote sensing of an O-type neutral line embedded in a current sheet. A source plasma with a tailward flowing Kappa distribution yields a strongly non-Kappa distribution after interacting with the neutral line: sharp jumps, or ridges, occur in the velocity space distribution function f(nu-perpendicular, nu-parallel) associated with both increases and decreases in f. The jumps occur when orbits are reversed in the x-direction: a reversal causing initially earthward particles (low probability in the source distribution) to be observed results in a decrease in f, while a reversal causing initially tailward particles to be observed produces an increase in f. The reversals, and hence the jumps, occur at approximately constant values of perpendicular velocity in both the positive nu parallel and negative nu parallel half planes. The results were obtained using single particle simulations in a fixed magnetic field model.
Beryllium and Boron abundances in population II stars
The scientific focus of this program was to undertake UV spectroscopic abundance analyses of extremely metal poor stars with attention to determining abundances of light elements such as beryllium and boron. The abundances are likely to reflect primordial abundances within the early galaxy and help to constrain models for early galactic nucleosynthesis. The general metal abundances of these stars are also important for understanding stellar evolution.
Age-Defying Star
An age-defying star called IRAS 19312+1950 exhibits features characteristic of a very young star and a very old star. The object stands out as extremely bright inside a large, chemically rich cloud of material, as shown in this image from NASA's Spitzer Space Telescope. IRAS 19312+1950 is the bright red star in the center of this image. A NASA-led team of scientists thinks the star -- which is about 10 times as massive as our sun and emits about 20,000 times as much energy -- is a newly forming protostar. That was a big surprise, because the region had not been known as a stellar nursery before. But the presence of a nearby interstellar bubble, which indicates the presence of a recently formed massive star, also supports this idea. http://photojournal.jpl.nasa.gov/catalog/PIA20914
NICER Eyes on Bursting Stars
What happens to a neutron stars accretion disk when its surface briefly explodes? A new instrument recently deployed at the International Space Station (ISS) is now watching bursts from neutron stars and reporting back.Deploying a New X-Ray MissionLaunch of NICER aboard a Falcon 9 rocket in June 2017. [NASA/Tony Gray]In early June of 2017, a SpaceX Dragon capsule on a Falcon 9 rocket launched on a resupply mission to the ISS. The pressurized interior of the Dragon contained the usual manifest of crew supplies, spacewalk equipment, and vehicle hardware. But the unpressurized trunk of the capsule held something a little different: the Neutron star Interior Composition Explorer (NICER).In the two weeks following launch, NICER was extracted from the SpaceX Dragon capsule and installed on the ISS. And by the end of the month, the instrument was already collecting its first data set: observations of a bright X-ray burst from Aql X-1, a neutron star accreting matter from a low-mass binary companion.Impact of BurstsNICERs goal is to provide a new view of neutron-star physics at X-ray energies of 0.212 keV a window that allows us to explore bursts of energy that neutron stars sometimes emit from their surfaces.Artists impression of an X-ray binary, in which a compact object accretes material from a companion star. [ESA/NASA/Felix Mirabel]In X-ray burster systems, hydrogen- and helium-rich material from a low-mass companion star piles up in an accretion disk around the neutron star. This material slowly funnels onto the neutron stars surface, forming a layer that gravitationally compresses and eventually becomes so dense and hot that runaway nuclear fusion ignites.Within seconds, the layer of material is burned up, producing a burst of emission from the neutron star that outshines even the inner regions of the hot accretion disk. Then more material funnels onto the neutron star and the process begins again.Though we have a good picture of the physics that causes these bursts
Nagyszombat and the stars
Zsoldos, E.
Péter Pázmány, founder of the University of Nagyszombat, considered stars in terms inherited from medieval times. The theses, connected to the university graduation, soon left this definition, and imagined stars as made from sublunar elements. The 1753 decree of the Empress Maria Theresia ordered university professors to publish textbooks. These textbooks, together with the theses showed a definite improvement, defining stars according to contemporary knowledge.
RR Lyrae type stars
Samus, N. N.
Basic observational data on RR Lyrae type stars are reviewed. It is noted that these stars are used widely to investigate the structure and kinematics of the spherical and intermediate components of the Galaxy, with correct data on the absolute magnitude of these variables being decisive. Attention is given to the relationship between the orbit eccentricity and inclination of osculating RR Lyrae type stars in the Galaxy and their metallicity index.
Star clusters in evolving galaxies
Renaud, Florent
Their ubiquity and extreme densities make star clusters probes of prime importance of galaxy evolution. Old globular clusters keep imprints of the physical conditions of their assembly in the early Universe, and younger stellar objects, observationally resolved, tell us about the mechanisms at stake in their formation. Yet, we still do not understand the diversity involved: why is star cluster formation limited to 105M⊙ objects in the Milky Way, while some dwarf galaxies like NGC 1705 are able to produce clusters 10 times more massive? Why do dwarfs generally host a higher specific frequency of clusters than larger galaxies? How to connect the present-day, often resolved, stellar systems to the formation of globular clusters at high redshift? And how do these links depend on the galactic and cosmological environments of these clusters? In this review, I present recent advances on star cluster formation and evolution, in galactic and cosmological context. The emphasis is put on the theory, formation scenarios and the effects of the environment on the evolution of the global properties of clusters. A few open questions are identified.
Introduction to neutron stars
Lattimer, James M.
Neutron stars contain the densest form of matter in the present universe. General relativity and causality set important constraints to their compactness. In addition, analytic GR solutions are useful in understanding the relationships that exist among the maximum mass, radii, moments of inertia, and tidal Love numbers of neutron stars, all of which are accessible to observation. Some of these relations are independent of the underlying dense matter equation of state, while others are very sensitive to the equation of state. Recent observations of neutron stars from pulsar timing, quiescent X-ray emission from binaries, and Type I X-ray bursts can set important constraints on the structure of neutron stars and the underlying equation of state. In addition, measurements of thermal radiation from neutron stars has uncovered the possible existence of neutron and proton superfluidity/superconductivity in the core of a neutron star, as well as offering powerful evidence that typical neutron stars have significant crusts. These observations impose constraints on the existence of strange quark matter stars, and limit the possibility that abundant deconfined quark matter or hyperons exist in the cores of neutron stars.
Strangeon and Strangeon Star
Xiaoyu, Lai; Renxin, Xu
The nature of pulsar-like compact stars is essentially a central question of the fundamental strong interaction (explained in quantum chromo-dynamics) at low energy scale, the solution of which still remains a challenge though tremendous efforts have been tried. This kind of compact objects could actually be strange quark stars if strange quark matter in bulk may constitute the true ground state of the strong-interaction matter rather than 56Fe (the so-called Witten's conjecture). From astrophysical points of view, however, it is proposed that strange cluster matter could be absolutely stable and thus those compact stars could be strange cluster stars in fact. This proposal could be regarded as a general Witten's conjecture: strange matter in bulk could be absolutely stable, in which quarks are either free (for strange quark matter) or localized (for strange cluster matter). Strange cluster with three-light-flavor symmetry is renamed strangeon, being coined by combining "strange nucleon� for the sake of simplicity. A strangeon star can then be thought as a 3-flavored gigantic nucleus, and strangeons are its constituent as an analogy of nucleons which are the constituent of a normal (micro) nucleus. The observational consequences of strangeon stars show that different manifestations of pulsarlike compact stars could be understood in the regime of strangeon stars, and we are expecting more evidence for strangeon star by advanced facilities (e.g., FAST, SKA, and eXTP).
Neutron stars contain the densest form of matter in the present universe. General relativity and causality set important constraints to their compactness. In addition, analytic GR solutions are useful in understanding the relationships that exist among the maximum mass, radii, moments of inertia, and tidal Love numbers of neutron stars, all of which are accessible to observation. Some of these relations are independent of the underlying dense matter equation of state, while others are very sensitive to the equation of state. Recent observations of neutron stars from pulsar timing, quiescent X-ray emission from binaries, and Type I X-ray bursts canmore » set important constraints on the structure of neutron stars and the underlying equation of state. In addition, measurements of thermal radiation from neutron stars has uncovered the possible existence of neutron and proton superfluidity/superconductivity in the core of a neutron star, as well as offering powerful evidence that typical neutron stars have significant crusts. These observations impose constraints on the existence of strange quark matter stars, and limit the possibility that abundant deconfined quark matter or hyperons exist in the cores of neutron stars.« less
Magnetic neutron star cooling and microphysics
Potekhin, A. Y.; Chabrier, G.
Aims: We study the relative importance of several recent updates of microphysics input to the neutron star cooling theory and the effects brought about by superstrong magnetic fields of magnetars, including the effects of the Landau quantization in their crusts. Methods: We use a finite-difference code for simulation of neutron-star thermal evolution on timescales from hours to megayears with an updated microphysics input. The consideration of short timescales (≲1 yr) is made possible by a treatment of the heat-blanketing envelope without the quasistationary approximation inherent to its treatment in traditional neutron-star cooling codes. For the strongly magnetized neutron stars, we take into account the effects of Landau quantization on thermodynamic functions and thermal conductivities. We simulate cooling of ordinary neutron stars and magnetars with non-accreted and accreted crusts and compare the results with observations. Results: Suppression of radiative and conductive opacities in strongly quantizing magnetic fields and formation of a condensed radiating surface substantially enhance the photon luminosity at early ages, making the life of magnetars brighter but shorter. These effects together with the effect of strong proton superfluidity, which slows down the cooling of kiloyear-aged neutron stars, can explain thermal luminosities of about a half of magnetars without invoking heating mechanisms. Observed thermal luminosities of other magnetars are still higher than theoretical predictions, which implies heating, but the effects of quantizing magnetic fields and baryon superfluidity help to reduce the discrepancy.
Disk Evaporation in Star Forming Regions
Hollenbach, David; DeVincenzi, Donald L. (Technical Monitor)
Young stars produce sufficient ultraviolet photon luminosity and mechanical luminosity in their winds to significantly affect the structure and evolution of the accretion disks surrounding them. The Lyman continuum photons create a nearly static, ionized, isothermal 10(exp 4) K atmosphere forms above the neutral disk at small distances from the star. Further out, they create a photoevaporative flow which relatively rapidly destroys the disk. The resulting slow (10-50 km/s) ionized outflow, which persists for approx. greater than 10(exp 5) years for disk masses M(sub d) approx. 0.3M(sub *), may explain the observational characteristics of many ultracompact HII regions. We compare model results to the observed radio free-free spectra and luminosities of ultracompact HII regions and to the interesting source MWC349, which is observed to produce hydrogen masers. We apply the results to Ae and Be stars in order to determine the lifetimes of disks around such stars. We also apply the results to the early solar nebula to explain the the dispersal of the solar nebula and the differences in hydrogen content in the giant planets. Finally, we model the small bright objects ("proplyds") observed in the Orion Nebula as disks around young, low mass stars which are externally illuminated by the UV photons from the nearby massive star Theta(sup 1) C.
Asteroid 'Bites the Dust' Around Dead Star
NASA's Spitzer Space Telescope set its infrared eyes upon the dusty remains of shredded asteroids around several dead stars. This artist's concept illustrates one such dead star, or 'white dwarf,' surrounded by the bits and pieces of a disintegrating asteroid. These observations help astronomers better understand what rocky planets are made of around other stars.
Asteroids are leftover scraps of planetary material. They form early on in a star's history when planets are forming out of collisions between rocky bodies. When a star like our sun dies, shrinking down to a skeleton of its former self called a white dwarf, its asteroids get jostled about. If one of these asteroids gets too close to the white dwarf, the white dwarf's gravity will chew the asteroid up, leaving a cloud of dust.
Spitzer's infrared detectors can see these dusty clouds and their various constituents. So far, the telescope has identified silicate minerals in the clouds polluting eight white dwarfs. Because silicates are common in our Earth's crust, the results suggest that planets similar to ours might be common around other stars.
Complex organic molecules and star formation
Bacmann, A.; Faure, A.
Star forming regions are characterised by the presence of a wealth of chemical species. For the past two to three decades, ever more complex organic species have been detected in the hot cores of protostars. The evolution of these molecules in the course of the star forming process is still uncertain, but it is likely that they are partially incorporated into protoplanetary disks and then into planetesimals and the small bodies of planetary systems. The complex organic molecules seen in star forming regions are particularly interesting since they probably make up building blocks for prebiotic chemistry. Recently we showed that these species were also present in the cold gas in prestellar cores, which represent the very first stages of star formation. These detections question the models which were until now accepted to account for the presence of complex organic molecules in star forming regions. In this article, we shortly review our current understanding of complex organic molecule formation in the early stages of star formation, in hot and cold cores alike and present new results on the formation of their likely precursor radicals.
Revisiting hypervelocity stars after Gaia DR2
Boubert, D.; Guillochon, J.; Hawkins, K.; Ginsburg, I.; Evans, N. W.; Strader, J.
Hypervelocity stars are intriguing rare objects traveling at speeds large enough to be unbound from the Milky Way. Several mechanisms have been proposed for producing them, including the interaction of the Galaxy's super-massive black hole (SMBH) with a binary; rapid mass-loss from a companion to a star in a short-period binary; the tidal disruption of an infalling galaxy and finally ejection from the Large Magellanic Cloud. While previously discovered high-velocity early-type stars are thought to be the result of an interaction with the SMBH, the origin of high-velocity late type stars is ambiguous. The second data release of Gaia (DR2) enables a unique opportunity to resolve this ambiguity and determine whether any late-type candidates are truly unbound from the Milky Way. In this paper, we utilize the new proper motion and velocity information available from DR2 to re-evaluate a collection of historical data compiled on the newly-created Open Fast Stars Catalog. We find that almost all previously-known high-velocity late-type stars are most likely bound to the Milky Way. Only one late-type object (LAMOST J115209.12+120258.0) is unbound from the Galaxy. Performing integrations of orbital histories, we find that this object cannot have been ejected from the Galactic centre and thus may be either debris from the disruption of a satellite galaxy or a disc runaway.
Failure of continuum methods for determining the effective temperature of hot stars
Hummer, D. G.; Abbott, David C.; Voels, Stephen A.; Bohannan, Bruce
It is demonstrated here that, for hot stars, methods based on the integrated continuum flux are completely unreliable discriminators of the effective temperature. Absorption line profiles provide much more accurate values of these parameters. It is not necessary to invoke nonradiative energy and momentum effects to explain the spectroscopic appearance of O-type stars of very different spectral type; rather, the observed spectra can be well modeled and fully interpreted by normal interaction of gas and radiation in stellar atmospheres of differing effective temperature and gravity.
Combinations of 148 navigation stars and the star tracker
Duncan, R.
The angular separation of all star combinations for 148 nav star on the onboard software for space transportation system-3 flight and following missions is presented as well as the separation of each pair that satisfies the viewing constraints of using both star trackers simultaneously. Tables show (1) shuttle star catalog 1980 star position in M 1950 coordinates; (2) two star combination of 148 nav stars; and (3) summary of two star-combinations of the star tracker 5 deg filter. These 148 stars present 10,875 combinations. For the star tracker filters of plus or minus 5 deg, there are 875 combinations. Formalhaut (nav star 26) has the best number of combinations, which is 33.
ATLASGAL: Chemical evolution of star forming clumps
Figura, Charles C.; Urquhart, James S.; Wyrowski, Friedrich
Although massive stars are few in number, they impact their host molecular clouds, clusters, and galaxies in profound ways, playing a vital role in regulating star formation in their host galaxy. Understanding the formation of these massive stars is critical to understanding this evolution, but their rapid early development causes them to reach the main sequence while still shrouded in their natal molecular cloud. Many studies have investigated these regions in a targeted manner, but a full understanding necessitates a broader view at all stages of formation across many star forming regions.We have used mid-infrared continuum surveys to guide selection of a statistically large sample of massive dust clumps from the 10,000 such clumps identified in the ATLASGAL Compact Source Catalogue (CSC), ensuring that all stages of the evolutionary process are included. A final sample of 600 fourth-quadrant sources within 1 degree of the Galactic plane were observed with the Mopra telescope with an 8 GHz bandwidth between 85.2 and 93.4 GHz.We present an overview of our results. We have identified over 30 molecular lines, seven of which with detected hyperfine structure, as well as several mm-radio recombination line transitions. Source velocities indicate that these regions trace the Crux-Scutum, Norma, and Carina Sagitarius arms. We have performed an analysis of linewidth and line intensity ratios, correlating these with star formation stages as identified by IR brightness at the 70 and 24 μm bands, and present several molecular pairs whose linewidth and intensity might serve as significant tracers of the evolutionary stage of star formation. We comment on the results of PCA analysis of the measured parameters for the overall population and the star formation stage subgroups with an eye toward characterising early stellar development through molecular line observations.
Large-scale Organized Magnetic Fields in O, B and A Stars
Mathys, G.
The status of our current knowledge of magnetic fields in stars of spectral types ranging from early F to O is reviewed. Fields with large-scale organised structure have now been detected and measured throughout this range. These fields are consistent with the oblique rotator model. In early F to late B stars, their occurrence is restricted to the subgroup of the Ap stars, which have the best studied fields among the early-type stars. Presence of fields with more complex topologies in other A and late B stars has been suggested, but is not firmly established. Magnetic fields have not been studied in a sufficient number of OB stars yet so as to establish whether they occur in all or only in some subset of these stars.
Rise of the First Super-Massive Stars
Regan, John A.; Downes, Turlough P.
We use high resolution adaptive mesh refinement simulations to model the formation of massive metal-free stars in the early Universe. By applying Lyman-Werner (LW) backgrounds of 100 J21 and 1000 J21 respectively we construct environments conducive to the formation of massive stars. We find that only in the case of the higher LW backgrounds are super-critical accretion rates realised that are necessary for super-massive star (SMS) formation. Mild fragmentation is observed for both backgrounds. Violent dynamical interactions between the stars that form in the more massive halo formed (1000 J21 background) results in the eventual expulsion of the two most massive stars from the halo. In the smaller mass halo (100 J21 background) mergers of stars occur before any multibody interactions and a single massive Pop III star is left at the centre of the halo at the end of our simulation. Feedback from the very massive Pop III stars is not effective in generating a large HII region with ionising photons absorbed within a few thousand AU of the star. In all cases a massive black hole seed is the expected final fate of the most massive objects. The seed of the massive Pop III star which remained at the centre of the less massive halo experiences steady accretion rates of almost 10-2M_{⊙}/yr and if these rates continue could potentially experience super-Eddington accretion rates in the immediate aftermath of collapsing into a black hole.
High-velocity runaway stars from three-body encounters
Gvaramadze, V. V.; Gualandris, A.; Portegies Zwart, S.
We performed numerical simulations of dynamical encounters between hard, massive binaries and a very massive star (VMS; formed through runaway mergers of ordinary stars in the dense core of a young massive star cluster) to explore the hypothesis that this dynamical process could be responsible for the origin of high-velocity (≥ 200 - 400 km s-1) early or late B-type stars. We estimated the typical velocities produced in encounters between very tight massive binaries and VMSs (of mass of ≥ 200 M⊙) and found that about 3 - 4% of all encounters produce velocities ≥ 400 km s-1, while in about 2% of encounters the escapers attain velocities exceeding the Milky Ways's escape velocity. We therefore argue that the origin of high-velocity (≥ 200 - 400 km s-1) runaway stars and at least some so-called hypervelocity stars could be associated with dynamical encounters between the tightest massive binaries and VMSs formed in the cores of star clusters. We also simulated dynamical encounters between tight massive binaries and single ordinary 50 - 100 M⊙ stars. We found that from 1 to ≃ 4% of these encounters can produce runaway stars with velocities of ≥ 300 - 400 km s-1 (typical of the bound population of high-velocity halo B-type stars) and occasionally (in less than 1% of encounters) produce hypervelocity (≥ 700 km s-1) late B-type escapers.
Identifying Young, Nearby Stars
Webb, Rich; Song, Inseok; Zuckerman, Ben; Bessell, Mike
Young stars have certain characteristics, e.g., high atmospheric abundance of lithium and chromospheric activity, fast rotation, distinctive space motion and strong X-ray flux compared to that of older main sequence stars. We have selected a list of candidate young (<100Myr) and nearby (<60pc) stars based on their space motion and/or strong X-ray flux. To determine space motion of a star, one needs to know its coordinates (RA, DEC), proper motion, distance, and radial velocity. The Hipparcos and Tycho catalogues provide all this information except radial velocities. We anticipate eventually searching approx. 1000 nearby stars for signs of extreme youth. Future studies of the young stars so identified will help clarify the formation of planetary systems for times between 10 and 100 million years. Certainly, the final output of this study will be a very useful resource, especially for adaptive optics and space based searches for Jupiter-mass planets and dusty proto-planetary disks. We have begun spectroscopic observations in January, 2001 with the 2.3 m telescope at Siding Spring Observatory (SSO) in New South Wales, Australia. These spectra will be used to determine radial velocities and other youth indicators such as Li 6708A absorption strength and Hydrogen Balmer line intensity. Additional observations of southern hemisphere stars from SSO are scheduled in April and northern hemisphere observations will take place in May and July at the Lick Observatory of the University of California. AT SSO, to date, we have observed about 100 stars with a high resolution spectrometer (echelle) and about 50 stars with a medium spectral resolution spectrometer (the "DBS"). About 20% of these stars turn out to be young stars. Among these, two especially noteworthy stars appear to be the closest T-Tauri stars ever identified. Interestingly, these stars share the same space motions as that of a very famous star with a dusty circumstellar disk--beta Pictoris. This new finding better
Merging strangeon stars
Lai, Xiao-Yu; Yu, Yun-Wei; Zhou, En-Ping; Li, Yun-Yang; Xu, Ren-Xin
The state of supranuclear matter in compact stars remains puzzling, and it is argued that pulsars could be strangeon stars. What would happen if binary strangeon stars merge? This kind of merger could result in the formation of a hyper-massive strangeon star, accompanied by bursts of gravitational waves and electromagnetic radiation (and even a strangeon kilonova explained in the paper). The tidal polarizability of binary strangeon stars is different from that of binary neutron stars, because a strangeon star is self-bound on the surface by the fundamental strong force while a neutron star by the gravity, and their equations of state are different. Our calculation shows that the tidal polarizability of merging binary strangeon stars is favored by GW170817. Three kinds of kilonovae (i.e., of neutron, quark and strangeon) are discussed, and the light curve of the kilonova AT 2017 gfo following GW170817 could be explained by considering the decaying strangeon nuggets and remnant star spin-down. Additionally, the energy ejected to the fireball around the nascent remnant strangeon star, being manifested as a gamma-ray burst, is calculated. It is found that, after a prompt burst, an X-ray plateau could follow in a timescale of 102 ‑ 103 s. Certainly, the results could be tested also by further observational synergies between gravitational wave detectors (e.g., Advanced LIGO) and X-ray telescopes (e.g., the Chinese HXMT satellite and eXTP mission), and especially if the detected gravitational wave form is checked by peculiar equations of state provided by the numerical relativistical simulation.
Deep Stromvil Photometry for Star Formation in the Head of the Pelican Nebula
Boyle, Richard P.; J., S.; Stott, J.; J., S.; Janusz, R.; J., S.; Straizys, V.
The North America and Pelican Nebulae, and specifically the dark cloud L935 contain regions of active star formation (Herbig, G. H. 1958, ApJ, 128,259). Previously we reported on Vatican telescope observations by Stromvil intermediate-band filters in a 12-arcmin field in the "Gulf of Mexico" region of L935. There we classify A, F, and G-type stars. However, the many faint K and M-type dwarf stars remain somewhat ambiguous in calibration and classification. But attaining reasonable progress, we turn to another part of L935 located near the Pelican head. This area includes the "bright rim" which is formed by dust and gas condensed by the light pressure of an unseen O-type star hidden behind the dense dark cloud. Straizys and Laugalys (2008 Baltic Astronomy, 17, 143 ) have identified this star to be one of the 2MASS objects with Av=23 mag. A few concentrations of faint stars, V 13 to 14 mag. are immersed in this dark region. Among these stars are a few known emission-line objects (T-Tauri or post T-Tauri stars). A half degree nearby are some photometric Vilnius standards we use to calibrate our new field. We call on 2MASS data for correlative information. Also the Stromvil photometry offers candidate stars for spectral observations. The aim of this study in the Vilnius and Stromvil photometric systems is to classify stars down to V = 18 mag., to confirm the existence of the young star clusters, and to determine the distance of the cloud covering the suspected hidden ionizing star.
Stars and Flowers, Flowers and Stars
Minti, Hari
The author, a graduated from the Bucharest University (1964), actually living and working in Israel, concerns his book to variable stars and flowers, two domains of his interest. The analogies includes double stars, eclipsing double stars, eclipses, Big Bang. The book contains 34 chapters, each of which concerns various relations between astronomy and other sciences and pseudosciences such as Psychology, Religion, Geology, Computers and Astrology (to which the author is not an adherent). A special part of the book is dedicated to archeoastronomy and ethnoastronomy, as well as to history of astronomy. Between the main points of interest of these parts: ancient sanctuaries in Sarmizegetusa (Dacia), Stone Henge(UK) and other. The last chapter of the book is dedicated to flowers. The book is richly illustrated. It is designed for a wide circle of readers.
How the First Stars Regulated Star Formation. II. Enrichment by Nearby Supernovae
Chen, Ke-Jung; Whalen, Daniel J.; Wollenberg, Katharina M. J.
Metals from Population III (Pop III) supernovae led to the formation of less massive Pop II stars in the early universe, altering the course of evolution of primeval galaxies and cosmological reionization. There are a variety of scenarios in which heavy elements from the first supernovae were taken up into second-generation stars, but cosmological simulations only model them on the largest scales. We present small-scale, high-resolution simulations of the chemical enrichment of a primordial halo by a nearby supernova after partial evaporation by the progenitor star. We find that ejecta from the explosion crash into and mix violently with ablativemore » flows driven off the halo by the star, creating dense, enriched clumps capable of collapsing into Pop II stars. Metals may mix less efficiently with the partially exposed core of the halo, so it might form either Pop III or Pop II stars. Both Pop II and III stars may thus form after the collision if the ejecta do not strip all the gas from the halo. The partial evaporation of the halo prior to the explosion is crucial to its later enrichment by the supernova.« less
Chen, Ke-Jung; Whalen, Daniel J.; Wollenberg, Katharina M. J.; Glover, Simon C. O.; Klessen, Ralf S.
Metals from Population III (Pop III) supernovae led to the formation of less massive Pop II stars in the early universe, altering the course of evolution of primeval galaxies and cosmological reionization. There are a variety of scenarios in which heavy elements from the first supernovae were taken up into second-generation stars, but cosmological simulations only model them on the largest scales. We present small-scale, high-resolution simulations of the chemical enrichment of a primordial halo by a nearby supernova after partial evaporation by the progenitor star. We find that ejecta from the explosion crash into and mix violently with ablative flows driven off the halo by the star, creating dense, enriched clumps capable of collapsing into Pop II stars. Metals may mix less efficiently with the partially exposed core of the halo, so it might form either Pop III or Pop II stars. Both Pop II and III stars may thus form after the collision if the ejecta do not strip all the gas from the halo. The partial evaporation of the halo prior to the explosion is crucial to its later enrichment by the supernova.
Stars Brewing in Cygnus X
A bubbling cauldron of star birth is highlighted in this image from NASA Spitzer Space Telescope. Massive stars have blown bubbles, or cavities, in the dust and gas -- a violent process that triggers both the death and birth of stars.
Spectroscopic studies of Wolf-Rayet stars. III - The WC subclass
Torres, A. V.; Conti, P. S.; Massey, P.
Wolf-Rayet (W-R) stars, which are the descendants of massive O-type stars, can be subdivided into three groups depending on their spectral appearance. These groups include the nitrogen class (WN), the carbon class (WC), and the oxygen class (WO). The present paper is concerned with the WC stars. The assignment of WC subtypes has been based on visual inspections of photographic plates. One of the aims of this study is related to the quantification of the visual estimates. The measured ratios of equivalent widths and the FWHM of the 4650 A line for Galactic and LMC stars are presented, and the reclassification of some stars is proposed on this basis. In particular, it is shown that the majority of the LMC WC stars should logically be classified WC4 instead of WC5. Comments on individual stars are provided, and terminal velocities are discussed. It is attempted to give a complete overview of the most important spectroscopic features of the WC stars in the optical region.
Deciphering the X-ray Emission of the Nearest Herbig Ae Star
Skinner, Stephen L.
In this research program, we obtained and analyzed an X-ray observation of the young nearby intermediate mass pre-main sequence star HD 104237 using the XMM-Newton space-based observatory. The observation was obtained on 17 Feb. 2002. This observation yielded high-quality X-ray images, spectra, and timing data which provided valuable information on the physical processes responsible for the X-ray emission. This star is a member of the group of so-called Herbig Ae/Be stars, which are young intermediate mass (approx. 2 - 4 solar masses) pre-main sequence (PMS) stars a few million years old that have not yet begun core hydrogen burning. The objective of the XMM-Newton observation was to obtain higher quality data than previously available in order to constrain possible X-ray emission mechanisms. The origin of the X-ray emission from Herbig Ae/Be stars is not yet known. These intermediate mass PMS stars lie on radiative tracks and are not expected to emit X-rays via solar-like magnetic processes, nor are their winds powerful enough to produce X-rays by radiative wind shocks as in more massive O-type stars. The emission could originate in unseen low-mass companions, or it may be intrinsic to the Herbig stars themselves if they still have primordial magnetic fields or can sustain magnetic activity via a nonsolar dynamo.
Young and Waltzing Binary Stars
other) - the detailed analysis showed that the distance between the two components is only 12 solar radii, or a little more than 8 million kilometres. If you would image yourself standing on the surface of the smaller star, the disk of the companion star would extend some 15° in the sky. This is 30 times larger than our view of the Sun! ADONIS observations The short orbital period and the even shorter duration of the eclipses, only 6 hours, posed a real challenge for the observers. They decided to obtain further high-angular resolution observations with the ADaptive Optics Near Infrared System (ADONIS) on the 3.6-m telescope at the ESO La Silla Observatory. Most fortunately, early ADONIS images demonstrated that this binary stellar system has a third companion, sufficiently far away from the two others to be seen as a separate star by ADONIS. This unexpected bonus made it possible to monitor the light changes of the binary system in great detail, by using the third companion as a convenient "reference" star. In December 2000 and January 2001, detailed ADONIS images of the RXJ 0529.4+0041 system were obtained in three near-infrared filters (the J-, H- and K-bands). ADONIS is equipped with the SHARP II camera and eliminates the adverse image-smearing effects of the atmospheric turbulence in real-time by means of a computer-controlled flexible mirror. As expected, the new, extremely sharp images of RXJ 0529.4+0041 greatly improved the achievable photometric precision. In particular, as the image of the third component was perfectly separated from the others, it did not "contaminate" the derived light curve of the eclipsing binary. The movie Primary eclipse Secondary eclipse ESO PR Photo 29a/01 ESO PR Photo 29a/01 [Preview - JPEG: 375 x 400 pix - 87k] [Normal - JPEG: 750 x 800 pix - 240k] ESO PR Photo 29d/01 ESO PR Photo 29d/01 [Preview - JPEG: 375 x 400 pix - 112k] [Normal - JPEG: 750 x 800 pix - 272k] ESO PR Photo 29b/01 ESO PR Photo 29b/01 [Preview - JPEG: 375 x 400 pix
Dusty Dead Star
A composite image from NASA Chandra and Spitzer space telescopes shows the dusty remains of a collapsed star, a supernova remnant called G54.1+0.3. The white source at the center is a dead star called a pulsar.
Science Through ARts (STAR)
Kolecki, Joseph; Petersen, Ruth; Williams, Lawrence
Science Through ARts (STAR) is an educational initiative designed to teach students through a multidisciplinary approach to learning. This presentation describes the STAR pilot project, which will use Mars exploration as the topic to be integrated. Schools from the United Kingdom, Japan, the United States, and possibly eastern Europe are expected to participate in the pilot project.
Star System Bonanza Illustration
This illustration shows the unusual orbit of planet Kepler-413b around a close pair of orange and red dwarf stars. The planet 66-day orbit is tilted 2.5 degrees with respect to the plane of the binary stars orbit.
Observing Double Stars
Genet, Russell M.; Fulton, B. J.; Bianco, Federica B.; Martinez, John; Baxter, John; Brewer, Mark; Carro, Joseph; Collins, Sarah; Estrada, Chris; Johnson, Jolyon; Salam, Akash; Wallen, Vera; Warren, Naomi; Smith, Thomas C.; Armstrong, James D.; McGaughey, Steve; Pye, John; Mohanan, Kakkala; Church, Rebecca
Double stars have been systematically observed since William Herschel initiated his program in 1779. In 1803 he reported that, to his surprise, many of the systems he had been observing for a quarter century were gravitationally bound binary stars. In 1830 the first binary orbital solution was obtained, leading eventually to the determination of stellar masses. Double star observations have been a prolific field, with observations and discoveries - often made by students and amateurs - routinely published in a number of specialized journals such as the Journal of Double Star Observations. All published double star observations from Herschel's to the present have been incorporated in the Washington Double Star Catalog. In addition to reviewing the history of visual double stars, we discuss four observational technologies and illustrate these with our own observational results from both California and Hawaii on telescopes ranging from small SCTs to the 2-meter Faulkes Telescope North on Haleakala. Two of these technologies are visual observations aimed primarily at published "hands-on" student science education, and CCD observations of both bright and very faint doubles. The other two are recent technologies that have launched a double star renaissance. These are lucky imaging and speckle interferometry, both of which can use electron-multiplying CCD cameras to allow short (30 ms or less) exposures that are read out at high speed with very low noise. Analysis of thousands of high speed exposures allows normal seeing limitations to be overcome so very close doubles can be accurately measured.
Densmore, Marycay; Kolecki, Joseph C.; Miller, Allan; Petersen, Ruth; Terrell, Mike
Science Through ARts (STAR) is a free, international, cross-curricular program thematically aligned with "The Vision for Space Exploration," a framework of goals and objectives published by NASA in February 2004. Through the STAR program, students in grades 5 through 12 are encouraged to apply their knowledge in creative ways as they approach a…
By Draconis Stars
Bopp, Bernard W.
An optical spectroscopic survey of dK-M stars has resulted in the discovery of several new H-alpha emission objects. Available optical data suggest these stars have a level of chromospheric activity midway between active BY Dra stars and quiet dM's. These "marginal" BY Dra stars are single objects that have rotation velocities slightly higher than that of quiet field stars but below that of active flare/BY Dra objects. The marginal BY Dra stars provide us with a class of objects rotating very near a "trigger velocity" (believed to be 5 km/s) which appears to divide active flare/BY Dra stars from quiet dM's. UV data on Mg II emission fluxes and strength of transition region features such as C IV will serve to fix activity levels in the marginal objects and determine chromosphere and transition-region heating rates. Simultaneous optical magnetic field measures will be used to explore the connection between fieldstrength/filling-factor and atmospheric heating. Comparison of these data with published information on active and quiet dM stars will yield information on the character of the stellar dynamo as it makes a transition from "low" to "high" activity.
How do stars form
Tscharnuter, W. M.
Modes and model concept of star formation are reviewed, beginning with the theory of Kant (1755), via Newton's exact mathematical formulation of the laws of motion, his recognition of the universal validity of general gravitation, to modern concepts and hypotheses. Axisymmetric and spherically symmetric collapse models are discussed, and the origin of double and multiple star systems is examined.
Nebraska STARS: Achieving Results
Roschewski, Pat; Isernhagen, Jody; Dappen, Leon
In 2000, the state of Nebraska passed legislation requiring the assessment of student performance on content standards, but its requirements were very different from those of any other state. Nebraska created what has come to be known as STARS (School-based Teacher-led Assessment and Reporting System). Under STARS, each of Nebraska's nearly 500…
OPTICAL SPECTROSCOPY OF X-RAY-SELECTED YOUNG STARS IN THE CARINA NEBULA
Vaidya, Kaushar; Chen, Wen-Ping; Lee, Hsu-Tai
We present low-resolution optical spectra for 29 X-ray sources identified as either massive star candidates or low-mass pre-main-sequence (PMS) star candidates in the clusters Trumpler 16 and Trumpler 14 of the Carina Nebula. Spectra of two more objects (one with an X-ray counterpart, and one with no X-ray counterpart), not originally our targets, but found close (∼3″) to two of our targets, are presented as well. Twenty early-type stars, including an O8 star, seven B1–B2 stars, two B3 stars, a B5 star, and nine emission-line stars, are identified. Eleven T Tauri stars, including eight classical T Tauri stars (CTTSs) and threemore » weak-lined T Tauri stars, are identified. The early-type stars in our sample are more reddened compared to the previously known OB stars of the region. The Chandra hardness ratios of our T Tauri stars are found to be consistent with the Chandra hardness ratios of T Tauri stars of the Orion Nebula Cluster. Most early-type stars are found to be nonvariable in X-ray emission, except the B2 star J104518.81–594217.9, the B3 star J104507.84–594134.0, and the Ae star J104424.76–594555.0, which are possible X-ray variables. J104452.20–594155.1, a CTTS, is among the brightest and the hardest X-ray sources in our sample, appears to be a variable, and shows a strong X-ray flare. The mean optical and near-infrared photometric variability in the V and K{sub s} bands, of all sources, is found to be ∼0.04 and 0.05 mag, respectively. The T Tauri stars show significantly larger mean variation, ∼0.1 mag, in the K{sub s} band. The addition of one O star and seven B1–B2 stars reported here contributes to an 11% increase of the known OB population in the observed field. The 11 T Tauri stars are the first ever confirmed low-mass PMS stars in the Carina Nebula region.« less
Observational Effects of Magnetism in O Stars: Surface Nitrogen Abundances
Martins, F.; Escolano, C.; Wade, G. A.; Donati, J. F.; Bouret, J. C.
Aims. We investigate the surface nitrogen content of the six magnetic O stars known to date as well as of the early B-type star Tau Sco.. We compare these abundances to predictions of evolutionary models to isolate the effects of magnetic field on the transport of elements in stellar interiors. Methods. We conduct a quantitative spectroscopic analysis of the ample stars with state-of-the-art atmosphere models. We rely on high signal-to-noise ratio, high resolution optical spectra obtained with ESPADONS at CFHT and NARVAL at TBL. Atmosphere models and synthetic spectra are computed with the code CMFGEN. Values of N/H together with their uncertainties are determined and compared to predictions of evolutionary models. Results. We find that the magnetic stars can be divided into two groups: one with stars displaying no N enrichment (one object); and one with stars most likely showing extra N enrichment (5 objects). For one star (Ori C) no robust conclusion can be drawn due to its young age. The star with no N enrichment is the one with the weakest magnetic field, possibly of dynamo origin. It might be a star having experienced strong magnetic braking under the condition of solid body rotation, but its rotational velocity is still relatively large. The five stars with high N content were probably slow rotators on the zero age main sequence, but they have surface N/H typical of normal O stars, indicating that the presence of a (probably fossil) magnetic field leads to extra enrichment. These stars may have a strong differential rotation inducing shear mixing. Our results shOuld be viewed as a basis on which new theoretical simulations can rely to better understand the effect of magnetism on the evolution of massive stars.
The Neutron Star Zoo
Harding, Alice K.
Neutron stars are a very diverse population, both in their observational and their physical properties. They prefer to radiate most of their energy at X-ray and gamma-ray wavelengths. But whether their emission is powered by rotation, accretion, heat, magnetic fields or nuclear reactions, they are all different species of the same animal whose magnetic field evolution and interior composition remain a mystery. This article will broadly review the properties of inhabitants of the neutron star zoo, with emphasis on their high-energy emission. XXX Neutron stars are found in a wide variety of sources, displaying an amazing array of behavior. They can be isolated or in binary systems, accreting, heating, cooling, spinning down, spinning up, pulsing, flaring and bursting. The one property that seems to determine their behavior most strongly is their magnetic field strength, structure and evolution. The hot polar caps, bursts and flares of magnetars are likely due to the rapid decay and twisting of their superstrong magnetic fields, whose very existence requires some kind of early dynamo activity. The intermediate-strength magnetic fields of RPPs determines their spin-down behavior and radiation properties. However, the overlap of the magnetar and RPP populations is not understood at present. Why don't high-field RPPs burst or flare? Why don't lower-field magnetars sometimes behave more like RPPs? INS may be old magnetars whose high fields have decayed, but they do not account for the existence of younger RPPs with magnetar-strength fields. Not only the strength of the magnetic field but also its configuration may be important in making a NS a magnetar or a RPP. Magnetic field decay is a critical link between other NS populations as well. "Decay" of the magnetic field is necessary for normal RPPs to evolve into MSPs through accretion and spin up in LMXBs. Some kind of accretion-driven field reduction is the most likely mechanism, but it is controversial since it is not
A window on first-stars models from studies of dwarf galaxies and galactic halo stars
Venkatesan, Aparna
Dwarf galaxies dominate the local universe by number and are predicted to be even more dominant at early times, with many having large star formation rates per unit mass. The cosmological role of dwarf galaxies in the metal enrichment and the reionization of the universe is an important but unresolved problem at present. Nearby low-mass galaxies are much more accessible observationally for detailed study and may be local analogs of the types of galaxies that hosted the first-light sources relevant for reionization. I will share recent results on UV studies of the escaping radiation from nearby low-mass starforming galaxies, as well as the tantalizing similarities in element abundance patterns between local dwarf galaxies and the latest data compilations on extremely metal-poor stars in galactic halos. I will highlight trends of interest in a variety of individual elements at values of [Fe/H] between -7 and -3, including alpha-elements, elements originating mostly in intermediate-mass stars, lithium, titanium, and r-process elements. These trends constrain not only models of the first stars and their supernovae, but provide a window into the physical conditions in early galaxies and when metal-free star formation may have ceased in the early universe.This work was supported by the University of San Francisco Faculty Development Fund, and NSF grant AST-1637339. We thank the Aspen Center for Physics, where some of this work was conducted, and which is supported by National Science Foundation grant PHY-1607611.
Young Star HD 141569
This image shows the dusty disk of planetary material surrounding the young star HD 141569, located 380 light-years away from Earth. It was taken using the vortex coronagraph on the W.M. Keck Observatory. The vortex suppressed light from the star in the center, revealing light from the innermost ring of planetary material around the star (blue). The disk around the star, made of olivine particles, extends from 23 to 70 astronomical units from the star. By comparison, Uranus is over 19 astronomical units from our sun, and Neptune about 30 astronomical units. One astronomical unit is the distance between Earth and our sun. http://photojournal.jpl.nasa.gov/catalog/PIA21090
'Marginal' BY Draconis stars
Spectroscopic observations of 52 dK-dM stars, obtained at 640-665 nm (with spectral resolution 70-90 pm) using CCD detectors on the coude-feed telescope at KPNO since 1982, are reported. Data for four stars found to have diluted absorption or weak emission above continuum at H-alpha are presented in tables and spectra and discussed in detail. These objects (Gliese numbers 256, 425A, 900, and 907.1) are shown to be 'marginal' BY Dra stars, single objects of age 2.5-3 Gyr with activity and rotational velocity (3-5 km/s) between those of normal dM stars and those of true BY Dra stars. An explanation based on evolution from the BY Dra stage through marginal BY Dra to inactive dM is proposed.
Rotating stars in relativity.
Paschalidis, Vasileios; Stergioulas, Nikolaos
Rotating relativistic stars have been studied extensively in recent years, both theoretically and observationally, because of the information they might yield about the equation of state of matter at extremely high densities and because they are considered to be promising sources of gravitational waves. The latest theoretical understanding of rotating stars in relativity is reviewed in this updated article. The sections on equilibrium properties and on nonaxisymmetric oscillations and instabilities in f -modes and r -modes have been updated. Several new sections have been added on equilibria in modified theories of gravity, approximate universal relationships, the one-arm spiral instability, on analytic solutions for the exterior spacetime, rotating stars in LMXBs, rotating strange stars, and on rotating stars in numerical relativity including both hydrodynamic and magnetohydrodynamic studies of these objects.
Activity Cycles in Stars
Hathaway, David H.
Starspots and stellar activity can be detected in other stars using high precision photometric and spectrometric measurements. These observations have provided some surprises (starspots at the poles - sunspots are rarely seen poleward of 40 degrees) but more importantly they reveal behaviors that constrain our models of solar-stellar magnetic dynamos. The observations reveal variations in cycle characteristics that depend upon the stellar structure, convection zone dynamics, and rotation rate. In general, the more rapidly rotating stars are more active. However, for stars like the Sun, some are found to be inactive while nearly identical stars are found to be very active indicating that periods like the Sun's Maunder Minimum (an inactive period from 1645 to 1715) are characteristic of Sun-like stars.
Producing Runaway Stars
How are the hypervelocity stars weve observed in our galaxy produced? A recent study suggests that these escapees could be accelerated by a massive black hole in the center of the Large Magellanic Cloud.A Black Hole SlingshotSince their discovery in 2005, weve observed dozens of candidate hypervelocity stars stars whose velocity in the rest frame of our galaxy exceeds the local escape velocity of the Milky Way. These stars present a huge puzzle: how did they attain these enormous velocities?One potential explanation is known as the Hills mechanism. In this process, a stellar binary is disrupted by a close encounter with a massive black hole (like those thought to reside at the center of every galaxy). One member of the binary is flung out of the system as a result of the close encounter, potentially reaching very large velocities.A star-forming region known as LHA 120-N 11, located within the LMC. Some binary star systems within the LMC might experience close encounters with a possible massive black hole at the LMCs center. [ESA/NASA/Hubble]Blame the LMC?Usually, discussions of the Hills mechanism assume that Sagittarius A*, the supermassive black hole at the center of the Milky Way, is the object guilty of accelerating the hypervelocity stars weve observed. But what if the culprit isnt Sgr A*, but a massive black hole at the center of the Large Magellanic Cloud (LMC), one of the Milky Ways satellite galaxies?Though we dont yet have evidence of a massive black hole at the center of the LMC, the dwarf galaxy is large enough to potentially host one as large as 100,000 solar masses. Assuming that it does, two scientists at the University of Cambridge, Douglas Boubert and Wyn Evans, have now modeled how this black hole might tear apart binary star systems and fling hypervelocity stars around the Milky Way.Models for AccelerationBoubert and Evans determined that the LMCs hypothetical black hole could easily eject stars at ~100 km/s, which is the escape velocity of the
Monte Carlo simulation of star/linear and star/star blends with chemically identical monomers
Theodorakis, P. E.; Avgeropoulos, A.; Freire, J. J.; Kosmas, M.; Vlahos, C.
The effects of chain size and architectural asymmetry on the miscibility of blends with chemically identical monomers, differing only in their molecular weight and architecture, are studied via Monte Carlo simulation by using the bond fluctuation model. Namely, we consider blends composed of linear/linear, star/linear and star/star chains. We found that linear/linear blends are more miscible than the corresponding star/star mixtures. In star/linear blends, the increase in the volume fraction of the star chains increases the miscibility. For both star/linear and star/star blends, the miscibility decreases with the increase in star functionality. When we increase the molecular weight of linear chains of star/linear mixtures the miscibility decreases. Our findings are compared with recent analytical and experimental results.
Massive runaway stars in the Large Magellanic Cloud
Gvaramadze, V. V.; Kroupa, P.; Pflamm-Altenburg, J.
problem of the origin of runaway stars and the early dynamical evolution of star clusters.
Formation of the First Stars and Blackholes
Yoshida, Naoki
Cosmic reionization is thought to be initiated by the first generation of stars and blackholes. We review recent progress in theoretical studies of early structure formation. Cosmic structure formation is driven by gravitational instability of primeval density fluctuations left over from Big Bang. At early epochs, there are baryonic streaming motions with significant relative velocity with respect to dark matter. The formation of primordial gas clouds is typically delayed by the streaming motions, but then physical conditions for the so-called direct collapse blackhole formation are realized in proto-galactic halos. We present a promising model in which intermediate mass blackholes are formed as early as z = 30.
Star Formation Activity Beyond the Outer Arm. I. WISE -selected Candidate Star-forming Regions
Izumi, Natsuko; Yasui, Chikako; Saito, Masao
The outer Galaxy beyond the Outer Arm provides a good opportunity to study star formation in an environment significantly different from that in the solar neighborhood. However, star-forming regions in the outer Galaxy have never been comprehensively studied or cataloged because of the difficulties in detecting them at such large distances. We studied 33 known young star-forming regions associated with 13 molecular clouds at R {sub G} ≥ 13.5 kpc in the outer Galaxy with data from the Wide-field Infrared Survey Explorer ( WISE ) mid-infrared all-sky survey. From their color distribution, we developed a simple identification criterion of star-forming regions inmore » the outer Galaxy with the WISE color. We applied the criterion to all the WISE sources in the molecular clouds in the outer Galaxy at R {sub G} ≥ 13.5 kpc detected with the Five College Radio Astronomy Observatory (FCRAO) {sup 12}CO survey of the outer Galaxy, of which the survey region is 102.°49 ≤ l  ≤ 141.°54, −3.°03 ≤ b  ≤ 5.°41, and successfully identified 711 new candidate star-forming regions in 240 molecular clouds. The large number of samples enables us to perform the statistical study of star formation properties in the outer Galaxy for the first time. This study is crucial to investigate the fundamental star formation properties, including star formation rate, star formation efficiency, and initial mass function, in a primordial environment such as the early phase of the Galaxy formation.« less
Modeling populations of rotationally mixed massive stars
Brott, I.
Stars: Rotation and Nitrogen Enrichment as the Key to Understanding Massive Star Evolution'', I.Hunter, I.Brott, D.J. Lennon, N. Langer, C. Trundle, A. de Koter, C.J. Evans and R.S.I. Ryans The Astrophysical Journal, 2008, 676, L29-L32 Ch. 4: ``The VLT-FLAMES Survey of Massive Stars: Constraints on Stellar Evolution from the Chemical Compositions of Rapidly Rotating Galactic and Magellanic Cloud B-type Stars '', I. Hunter, I. Brott, N. Langer, D.J. Lennon, P.L. Dufton, I.D. Howarth R.S.I. Ryan, C. Trundle, C. Evans, A. de Koter and S.J. Smartt Published in Astronomy & Astropysics, 2009, 496, 841- 853 Ch. 5: ``Rotating Massive Main-Sequence Stars II: Simulating a Population of LMC early B-type Stars as a Test of Rotational Mixing '', I. Brott, C. J. Evans, I. Hunter, A. de Koter, N. Langer, P. L. Dufton, M. Cantiello, C. Trundle, D. J. Lennon, S.E. de Mink, S.-C. Yoon, P. Anders submitted to Astronomy & Astrophysics Ch 6: ``The Nature of B Supergiants: Clues From a Steep Drop in Rotation Rates at 22 000 K - The possibility of Bi-stability braking'', Jorick S. Vink, I. Brott, G. Graefener, N. Langer, A. de Koter, D.J. Lennon Astronomy & Astrophysics, 2010, 512, L7
Carbon Atmosphere Discovered On Neutron Star
without pulsations would require a tiny size, consistent only with exotic stars made of strange quark matter. "Our carbon veil solves one of the big questions about the neutron star in Cas A," said Craig Heinke. "People have been willing to consider some weird explanations, so it's a relief to discover a less peculiar solution." Unlike most astronomical objects, neutron stars are small enough to understand on a human scale. For example, neutron stars typically have a diameter of about 14 miles, only slightly longer than a half-marathon. The atmosphere of a neutron star is on an even smaller scale. The researchers calculate that the carbon atmosphere is only about 4 inches thick, because it has been compressed by a surface gravity that is 100 billion times stronger than on Earth. "For people who are used to hearing about immense sizes of things in space, it might be a surprise that we can study something so small," said Ho. "It's also funny to think that such a thin veil over this star played a key role in frustrating researchers." In Earth's time frame, the estimated age of the neutron star in Cas A is only several hundred years, making it about ten times younger than other neutron stars with detected surface emission. Therefore, the Cas A neutron star gives a unique window into the early life of a cooling neutron star. The carbon itself comes from a combination of material that has fallen back after the supernova, and nuclear reactions on the hot surface of the neutron star which convert hydrogen and helium into carbon. The X-ray spectrum and lack of pulsar activity suggest that the magnetic field on the surface of this neutron star is relatively weak. Similarly low magnetic fields are implied for several other young neutron stars by study of their weak X-ray pulsations. It is not known whether these neutron stars will have low magnetic fields for their entire lives, and never become radio pulsars, or whether processes in their interior will lead to the development of
The Infrared Spectral Region of Stars
Jaschek, Carlos; Andrillat, Y.
1. Stars in the infrared: results from IRAS H. J. G. L. M. Lamers and L. B. F. M. Watera; 2. What is expected from ISO J. P. Baluteau; 3. New infrared instrumentation S. Bensammar; 4. High resolution atomic spectroscopy in the infrared and its application to astrophysics S. Johansson; 5. Spectroscopy of early -type stars C. Jaschek; 6. Spectroscopy of late type stars U. F. Jøgensen; 7. Dust formation and evolution in circumstellar media J. P. J. Lafon; 8. The infrared solar spectrum N. Grevesse; 9. Symbiotic and related objects M. Hack; 10. Stellar photometry and spectrophotometry in the infrared R. F. Wing; 11. Stellar variability in the infrared A. Evans; 12. Circumstellar material in main sequence H. H. Aamann.
Making star teams out of star players.
Mankins, Michael; Bird, Alan; Root, James
Top talent is an invaluable asset: In highly specialized or creative work, for instance, "A" players are likely to be six times as productive as "B" players. So when your company has a crucial strategic project, why not multiply all that firepower and have a team of your best performers tackle it? Yet many companies hesitate to do this, believing that all-star teams don't work: Big egos will get in the way. The stars won't be able to work with one another. They'll drive the team Leader crazy. Mankins, Bird, and Root of Bain & Company believe it's time to set aside that thinking. They have seen all-star teams do extraordinary work. But there is a right way and a wrong way to organize them. Before you can even begin to assemble such a team, you need to have the right talent management practices, so you hire and develop the best people and know what they're capable of. You have to give the team appropriate incentives and leaders and support staffers who are stars in their own right. And projects that are ill-defined or small scale are not for all-star teams. Use them only for critical missions, and make sure their objectives are clear. Even with the right setup, things can still go wrong. The wise executive will take steps to manage egos, prune non-team-players, and prevent average coworkers from feeling completely undervalued. She will also invest a lot of time in choosing the right team Leader and will ask members for lots of feedback to monitor how that leader is doing.
Optical-NIR dust extinction towards Galactic O stars
Maíz Apellániz, J.; Barbá, R. H.
Context. O stars are excellent tracers of the intervening ISM because of their high luminosity, blue intrinsic SED, and relatively featureless spectra. We are currently conducting the Galactic O-Star Spectroscopic Survey (GOSSS), which is generating a large sample of O stars with accurate spectral types within several kpc of the Sun. Aims: We aim to obtain a global picture of the properties of dust extinction in the solar neighborhood based on optical-NIR photometry of O stars with accurate spectral types. Methods: We have processed a carefully selected photometric set with the CHORIZOS code to measure the amount [E(4405 - 5495)] and type [R5495] of extinction towards 562 O-type stellar systems. We have tested three different families of extinction laws and analyzed our results with the help of additional archival data. Results: The Maíz Apellániz et al. (2014, A&A, 564, A63) family of extinction laws provides a better description of Galactic dust that either the Cardelli et al. (1989, ApJ, 345, 245) or Fitzpatrick (1999, PASP, 111, 63) families, so it should be preferentially used when analysing samples similar to the one in this paper. In many cases O stars and late-type stars experience similar amounts of extinction at similar distances but some O stars are located close to the molecular clouds left over from their births and have larger extinctions than the average for nearby late-type populations. In qualitative terms, O stars experience a more diverse extinction than late-type stars, as some are affected by the small-grain-size, low-R5495 effect of molecular clouds and others by the large-grain-size, high-R5495 effect of H II regions. Late-type stars experience a narrower range of grain sizes or R5495, as their extinction is predominantly caused by the average, diffuse ISM. We propose that the reason for the existence of large-grain-size, high-R5495 regions in the ISM in the form of H II regions and hot-gas bubbles is the selective destruction of small dust
Dense Axion Stars.
Braaten, Eric; Mohapatra, Abhishek; Zhang, Hong
If the dark matter particles are axions, gravity can cause them to coalesce into axion stars, which are stable gravitationally bound systems of axions. In the previously known solutions for axion stars, gravity and the attractive force between pairs of axions are balanced by the kinetic pressure. The mass of these dilute axion stars cannot exceed a critical mass, which is about 10^{-14}M_{⊙} if the axion mass is 10^{-4}  eV. We study axion stars using a simple approximation to the effective potential of the nonrelativistic effective field theory for axions. We find a new branch of dense axion stars in which gravity is balanced by the mean-field pressure of the axion Bose-Einstein condensate. The mass on this branch ranges from about 10^{-20}M_{⊙} to about M_{⊙}. If a dilute axion star with the critical mass accretes additional axions and collapses, it could produce a bosenova, leaving a dense axion star as the remnant.
Heartbeat Stars Artist Concept
This artist's concept depicts "heartbeat stars," which have been detected by NASA's Kepler Space Telescope and others. The illustration shows two heartbeat stars swerving close to one another in their closest approach along their highly elongated orbits around one another. The mutual gravitation of the two stars would cause the stars themselves to become slightly ellipsoidal in shape. A third, more distant star in the system is shown in the upper left. Astronomers speculate that such unseen companions may exist in some of these heartbeat star systems, and could be responsible for maintaining these oddly stretched-out orbits. The overlaid curve depicts the inferred cyclic change in velocities in one such system, called KIC 9965691, looking something like the graph of an electrocardiogram (hence the name "heartbeat stars"). The solid points represent measurements made by the HIRES instrument at the W.M. Keck Observatory, and the curve is the best fit model for the motions of this system. http://photojournal.jpl.nasa.gov/catalog/PIA21075
Course 6: Star Formation
Natta, A.
Contents 1 Introduction 2 Collapse of molecular cores 2.1 Giant molecular clouds and cores 2.2 Conditions for collapse 2.3 Free-fall collapse 2.4 Collapse of an isothermal sphere of gas 2.5 Collapse of a slowly rotating core 3 Observable properties of protostars 3.1 Evidence of infall from molecular line profiles 3.2 SEDs of protostars 3.3 The line spectrumof a protostar 4 Protostellar and pre-main-sequence evolution 4.1 The protostellar phase 4.2 Pre-main-sequence evolution 4.3 The birthline 5 Circumstellar disks 5.1 Accretion disks 5.2 Properties of steady accretion disks 5.3 Reprocessing disks 5.4 Disk-star interaction 6 SEDs of disks 6.1 Power-law disks 6.2 Long-wavelength flux and disk mass 6.3 Comparison with TTS observations: Heating mechanism 7 Disk properties from observations 7.1 Mass accretion rate 7.2 Inner radius 7.3 Masses 7.4 Sizes 8 Disk lifetimes 8.1 Ground-based near and mid-infrared surveys 8.2 Mid-infrared ISOCAMsurveys 8.3 ISOPHOT 60 microm survey 8.4 Surveys at millimeter wavelengths 9 Disk evolution 9.1 Can we observe the early planet formation phase? 9.2 Evidence for grain growth 9.3 Evidence of planetesimals 9.4 Where is the diskmass? 10 Secondary or debris disks 11 Summary
A modern search for Wolf-Rayet stars in the Magellanic Clouds: First results
Massey, Philip; Neugent, Kathryn F.; Morrell, Nidia
Over the years, directed surveys and incidental spectroscopy have identified 12 Wolf-Rayet (WR) stars in the Small Magellanic Cloud (SMC) and 139 in the Large Magellanic Cloud (LMC), numbers which are often described as 'essentially complete'. Yet, new WRs are discovered in the LMC almost yearly. We have therefore initiated a new survey of both Magellanic Clouds using the same interference-filter imaging technique previously applied to M31 and M33. We report on our first observing season, in which we have successfully surveyed ∼15% of our intended area of the SMC and LMC. Spectroscopy has confirmed nine newly found WRs inmore » the LMC (a 6% increase), including one of WO-type, only the third known in that galaxy and the second to be discovered recently. The other eight are WN3 stars that include an absorption component. In two, the absorption is likely from an O-type companion, but the other six are quite unusual. Five would be classified naively as 'WN3+O3 V', but such a pairing is unlikely given the rarity of O3 stars, the short duration of this phase (which is incommensurate with the evolution of a companion to a WN star), and because these stars are considerably fainter than O3 V stars. The sixth star may also fall into this category. CMFGEN modeling suggests these stars are hot, bolometrically luminous, and N-rich like other WN3 stars, but lack the strong winds that characterize WNs. Finally, we discuss two rare Of?p stars and four Of supergiants we found, and propose that the B[e] star HD 38489 may have a WN companion.« less
Einstein Observations of X-ray emission from A stars
Golub, L.; Harnden, F. R., Jr.; Maxson, C. W.; Rosner, R.; Vaiana, G. S.; Cash, W., Jr.; Snow, T. P., Jr.
Results are reported from the combined CfA Stellar Survey of selected bright A stars and an Einstein Guest Observer program for Ap and Am stars. In an initial report of results from the CfA Stellar Surveys by Vaiana et al. (1981) it was noted that the spread in observed X-ray luminosities among the few A stars observed was quite large. The reasons for this large spread was studied by Pallavicini et al. (1981). It was found that the X-ray emission from normal stars is related very strongly to bolometric luminosity for early-type stars and to rotation rate for late-type stars. However, an exception to this rule has been the apparently anomalous behavior of A star X-ray emission, for which the large spread in luminosity showed no apparent correlation with either bolometric luminosity or stellar rotation rate. In the present study, it is shown that the level of emission from normal A stars agrees with the correlation observed for O and B stars.
Mind Your Ps and Qs: The Interrelation between Period (P) and Mass-ratio (Q) Distributions of Binary Stars
Moe, Maxwell; Di Stefano, Rosanne
We compile observations of early-type binaries identified via spectroscopy, eclipses, long-baseline interferometry, adaptive optics, common proper motion, etc. Each observational technique is sensitive to companions across a narrow parameter space of orbital periods P and mass ratios q = {M}{comp}/M 1. After combining the samples from the various surveys and correcting for their respective selection effects, we find that the properties of companions to O-type and B-type main-sequence (MS) stars differ among three regimes. First, at short orbital periods P ≲ 20 days (separations a ≲ 0.4 au), the binaries have small eccentricities e ≲ 0.4, favor modest mass ratios < q> ≈ 0.5, and exhibit a small excess of twins q > 0.95. Second, the companion frequency peaks at intermediate periods log P (days) ≈ 3.5 (a ≈ 10 au), where the binaries have mass ratios weighted toward small values q ≈ 0.2-0.3 and follow a Maxwellian "thermal� eccentricity distribution. Finally, companions with long orbital periods log P (days) ≈ 5.5-7.5 (a ≈ 200-5000 au) are outer tertiary components in hierarchical triples and have a mass ratio distribution across q ≈ 0.1-1.0 that is nearly consistent with random pairings drawn from the initial mass function. We discuss these companion distributions and properties in the context of binary-star formation and evolution. We also reanalyze the binary statistics of solar-type MS primaries, taking into account that 30% ± 10% of single-lined spectroscopic binaries likely contain white dwarf companions instead of low-mass stellar secondaries. The mean frequency of stellar companions with q > 0.1 and log P (days) < 8.0 per primary increases from 0.50 ± 0.04 for solar-type MS primaries to 2.1 ± 0.3 for O-type MS primaries. We fit joint probability density functions f({M}1,q,P,e)\
Highly-evolved stars
Heap, S. R.
The ways in which the IUE has proved useful in studying highly evolved stars are reviewed. The importance of high dispersion spectra for abundance analyses of the sd0 stars and for studies of the wind from the central star of NGC 6543 and the wind from the 0 type component of Vela X-1 is shown. Low dispersion spectra are used for absolute spectrophotometry of the dwarf nova, Ex Hya. Angular resolution is important for detecting and locating UV sources in globular clusters.
Massive star formation at high spatial resolution
Pascucci, Ilaria
This thesis studies the early phases of massive stars and their impact on the surrounding. The capabilities of continuum radiative transfer (RT) codes to interpret the observations are also investigated. The main results of this work are: 1) Two massive star-forming regions are observed in the infrared. The thermal emission from the ultra-compact H II regions is resolved and the spectral type of the ionizing stars is estimated. The hot cores are not detected thus implying line-of-sight extinction larger than 200 visual magnitude. 2) The first mid-infrared interferometric measurements towards a young massive star resolve thermal emission on scales of 30-50 AU probing the size of the predicted disk. The visibility curve differs from those of intermediate-mass stars. 3) The close vicinity of Θ1C Ori are imaged using the NACO adaptive optics system. The binary proplyd Orion 168-326 and its interaction with the wind from Θ1C Ori are resolved. A proplyd uniquely seen face-on is also identified. 4) Five RT codes are compared in a disk configuration. The solutions provide the first 2D benchmark and serve to test the reliability of other RT codes. The images/visibilities from two RT codes are compared for a distorted disk. The parameter range in which such a distortion is detectable with MIDI is explored.
RCW 36 in the Vela Molecular Ridge: Evidence for high-mass star-cluster formation triggered by cloud-cloud collision
Sano, Hidetoshi; Enokiya, Rei; Hayashi, Katsuhiro; Yamagishi, Mitsuyoshi; Saeki, Shun; Okawa, Kazuki; Tsuge, Kisetsu; Tsutsumi, Daichi; Kohno, Mikito; Hattori, Yusuke; Yoshiike, Satoshi; Fujita, Shinji; Nishimura, Atsushi; Ohama, Akio; Tachihara, Kengo; Torii, Kazufumi; Hasegawa, Yutaka; Kimura, Kimihiro; Ogawa, Hideo; Wong, Graeme F.; Braiding, Catherine; Rowell, Gavin; Burton, Michael G.; Fukui, Yasuo
A collision between two molecular clouds is one possible candidate for high-mass star formation. The H II region RCW 36, located in the Vela molecular ridge, contains a young star cluster (˜ 1 Myr old) and two O-type stars. We present new CO observations of RCW 36 made with NANTEN2, Mopra, and ASTE using 12CO(J = 1-0, 2-1, 3-2) and 13CO(J = 2-1) emission lines. We have discovered two molecular clouds lying at the velocities VLSR ˜ 5.5 and 9 km s-1. Both clouds are likely to be physically associated with the star cluster, as verified by the good spatial correspondence among the two clouds, infrared filaments, and the star cluster. We also found a high intensity ratio of ˜ 0.6-1.2 for CO J = 3-2/1-0 toward both clouds, indicating that the gas temperature has been increased due to heating by the O-type stars. We propose that the O-type stars in RCW 36 were formed by a collision between the two clouds, with a relative velocity separation of 5 km s-1. The complementary spatial distributions and the velocity separation of the two clouds are in good agreement with observational signatures expected for O-type star formation triggered by a cloud-cloud collision. We also found a displacement between the complementary spatial distributions of the two clouds, which we estimate to be 0.3 pc assuming the collision angle to be 45° relative to the line-of-sight. We estimate the collision timescale to be ˜ 105 yr. It is probable that the cluster age found by Ellerbroek et al. (2013b, A&A, 558, A102) is dominated by the low-mass members which were not formed under the triggering by cloud-cloud collision, and that the O-type stars in the center of the cluster are explained by the collisional triggering independently from the low-mass star formation.
FEROS Finds a Strange Star
Solar System. The study of stars in this cluster provides important information about the chemical evolution of the Milky Way galaxy. The significance of Lithium Lithium is not a very common element in daily life (except in batteries and certain medical drugs), but it is of great interest in astronomy. It is the heaviest element that is supposed to have been created in measurable quantities in the early Universe, soon after the Big Bang. All stars destroy most of their Lithium soon after their formation, although some manage to produce this element again at a later stage of their evolution [1]. There may be a substantial loss of Lithium from evolved stars into the interstellar medium (ISM). This element is indeed observed in the ISM. Calculations have shown that the primordial (original) abundance of Lithium was about ten times less than what is now measured in the ISM. The present abundance of Lithium in the Sun is over 100 times less than in the ISM. Large quantities of this element would certainly not be expected in a star as old as S50, especially since violent motions in the atmospheres of such giant stars very efficiently mix the material in the upper layers with that from the star's inner regions where the ongoing nuclear processes quickly destroy any Lithium. Still, the FEROS spectra show the presence in S50 of Lithium in quantities similar to that in the ISM - or in the proto-solar nebula from which the Sun and the planets formed, about 4,600 million years ago! The spectra of many hundreds of giant stars in the solar neighbourhood have been recorded, but only a few have shown such an unusual presence of Lithium. This is the first time that a Lithium rich giant star has been found in a stellar cluster and for which a comparatively accurate age can be determined. In fact, S50 appears to contain more of this fragile element than any other giant star observed so far. What is the origin of the Lithium in S50? How can this unexpected observation be explained? The
Hubble Captures Bubbles And Baby Stars
Image release June 22, 2010 A spectacular new NASA/ESA Hubble Space Telescope image — one of the largest ever released of a star-forming region — highlights N11, part of a complex network of gas clouds and star clusters within our neighbouring galaxy, the Large Magellanic Cloud. This region of energetic star formation is one of the most active in the nearby Universe. The Large Magellanic Cloud contains many bright bubbles of glowing gas. One of the largest and most spectacular has the name LHA 120-N 11, from its listing in a catalogue compiled by the American astronomer and astronaut Karl Henize in 1956, and is informally known as N11. Close up, the billowing pink clouds of glowing gas make N11 resemble a puffy swirl of fairground candy floss. From further away, its distinctive overall shape led some observers to nickname it the Bean Nebula. The dramatic and colourful features visible in the nebula are the telltale signs of star formation. N11 is a well-studied region that extends over 1000 light-years. It is the second largest star-forming region within the Large Magellanic Cloud and has produced some of the most massive stars known. It is the process of star formation that gives N11 its distinctive look. Three successive generations of stars, each of which formed further away from the centre of the nebula than the last, have created shells of gas and dust. These shells were blown away from the newborn stars in the turmoil of their energetic birth and early life, creating the ring shapes so prominent in this image. Beans are not the only terrestrial shapes to be found in this spectacular high resolution image from the NASA/ESA Hubble Space Telescope. In the upper left is the red bloom of nebula LHA 120-N 11A. Its rose-like petals of gas and dust are illuminated from within, thanks to the radiation from the massive hot stars at its centre. N11A is relatively compact and dense and is the site of the most recent burst of star development in the region. Other star
Mass loss from hot, luminous stars
Burnley, Adam Warwick
A general enquiry into the physics of mass loss from hot, luminous stars is presented. Ha spectroscopy of 64 Galactic early-type stars has been obtained using the telescopes of the Isaac Newton Group (ING) and the Anglo-Australian Observatory (AAO). The sample was selected to include objects with published radio and/or mm fluxes. The Halpha observations are quantitatively modelled using a modified version of the FORSOL code developed by Puls et al. (1996). FORSOL has been coupled with the PIKAIA subroutine (Charbonneau and Knapp, 1996) to create PHALTEE (Program for Halpha Line Transfer with Eugenic Estimation), in order to search a specified parameter space for the 'best' (quasi- least-squares) model fit to the data, using a genetic algorithm. This renders Ha modelling both more objective and automated. Where possible, both mass-loss rates and velocity field beta-exponents are determined for the sample. New mm-wave observations of nineteen Galactic early-type stars, including a subset of the Halpha sample, have been obtained using the Sub-millimetre Common User Bolometer Array (SCUBA). Where possible, mean fluxes are calculated, and these data used with the results of a literature survey of mm and cm fluxes to determine mass-loss rates for a larger sample, of 53 Galactic early-type stars. The incidence of nonthermal emission is examined, with 23% of the sample exhibiting strong evidence for nonthermal flux. The occurrence of binarity and excess X-ray emission amongst the nonthermal emitters is also investigated. For the subset of 36 stars common to both the Halpha and mm/radio samples, the results permit a comparison of mass-loss rates derived using diagnostics that probe the wind conditions at different radial depths. A mean value of log (Mradio/MHalpha) = 0.02 +/- 0.05 is obtained for the thermal radio emitters. The wind-momentum-luminosity relationship (WLR) for the sample is also investigated.
Hot-Jupiter Breakfasts Realign Stars
Two researchers at the University of Chicago have recently developed a new theory to explain an apparent dichotomy in the orbits of planets around cool vs. hot stars. Their model proposes that the spins of cool stars are affected when they ingest hot Jupiters (HJs) early in their stellar lifetimes. A Puzzling Dichotomy: In exoplanet studies, there is a puzzling difference observed between planet orbits around cool and hot (those with Teff ≥ 6250 K) stars: the orbital planes of planets around cool stars are primarily aligned with the host star's spin, whereas the orbital planes of planets around hot stars seem to be randomly distributed. Previous attempts to explain this dichotomy have focused on tidal interactions between the host star and the planets observed in the system. Now Titos Matsakos and Arieh Königl have taken these models a step further — by including in their calculations not only the effects of observed planets, but also those of HJs that may have been swallowed by the star long before we observed the systems. Modeling Meals: Plots of the distribution of the obliquity λ for hot Jupiters around cool hosts (upper plot) and hot hosts (lower plot). The dashed line shows the initial distribution, the bins show the model prediction for the final distribution after the systems evolve, and the black dots show the current observational data. [Matsakos & Königl, 2015]" class="size-thumbnail wp-image-223" height="386" src="http://aasnova.org/wp-content/uploads/2015/08/fig22-260x386.png" width="260" /> Plots of the distribution of the obliquity λ for hot Jupiters around cool hosts (upper plot) and hot hosts (lower plot). The dashed line shows the initial distribution, the bins show the model prediction for the final distribution after the systems evolve, and the black dots show the current observational data. [Matsakos & Königl, 2015] The authors' model assumes that as HJs are formed and migrate inward through the protoplanetary disk, they stall out near
AgSTAR
AgSTAR promotes biogas recovery projects, which generate renewable energy and other beneficial products from the anaerobic digestion of livestock manure and organic wastes while decreasing greenhouse gas emissions from the agriculture sector.
Planets Around Neutron Stars
Wolszczan, Alexander; Kulkarni, Shrinivas R; Anderson, Stuart B.
The objective of this proposal was to continue investigations of neutron star planetary systems in an effort to describe and understand their origin, orbital dynamics, basic physical properties and their relationship to planets around normal stars. This research represents an important element of the process of constraining the physics of planet formation around various types of stars. The research goals of this project included long-term timing measurements of the planets pulsar, PSR B1257+12, to search for more planets around it and to study the dynamics of the whole system, and sensitive searches for millisecond pulsars to detect further examples of old, rapidly spinning neutron stars with planetary systems. The instrumentation used in our project included the 305-m Arecibo antenna with the Penn State Pulsar Machine (PSPM), the 100-m Green Bank Telescope with the Berkeley- Caltech Pulsar Machine (BCPM), and the 100-m Effelsberg and 64-m Parkes telescopes equipped with the observatory supplied backend hardware.
Cooling of neutron stars
Pethick, C. J.
It is at present impossible to predict the interior constitution of neutron stars based on theory and results from laboratory studies. It has been proposed that it is possible to obtain information on neutron star interiors by studying thermal radiation from their surfaces, because neutrino emission rates, and hence the temperature of the central part of a neutron star, depend on the properties of dense matter. The theory predicts that neutron stars cool relatively slowly if their cores are made up of nucleons, and cool faster if the matter is in an exotic state, such as a pion condensate, a kaon condensate, or quark matter. This view has recently been questioned by the discovery of a number of other processes that could lead to copious neutrino emission and rapid cooling.
Tabby's Star (Illustration)
This illustration depicts a hypothetical uneven ring of dust orbiting KIC 8462852, also known as Boyajian's Star or Tabby's Star. Astronomers have found the dimming of the star over long periods appears to be weaker at longer infrared wavelengths of light and stronger at shorter ultraviolet wavelengths. Such reddening is characteristic of dust particles and inconsistent with more fanciful "alien megastructure" concepts, which would evenly dim all wavelengths of light. By studying observations from NASA's Spitzer and Swift telescopes, as well as the Belgian AstroLAB IRIS observatory, the researchers have been able to better constrain the size of the dust particles. This places them within the range found in dust disks orbiting stars, and larger than the particles typically found in interstellar dust. The system is portrayed with a couple of comets, consistent with previous studies that have found evidence for cometary activity within the system. https://photojournal.jpl.nasa.gov/catalog/PIA22081
Winds from cool stars
Dupree, A. K.
Spectral observations of cool stars enable study of the presence and character of winds and the mass loss process in objects with effective temperatures, gravities, and atmospheric compositions which differ from that of the Sun. A wealth of recent spectroscopic measurements from the Hubble Space Telescope, and the Extreme Ultraviolet Explorer complement high resolution ground-based measures in the optical and infrared spectral regions. Such observations when combined with realistic semi-empirical atmospheric modeling allow us to estimate the physical conditions in the atmospheres and winds of many classes of cool stars. Line profiles support turbulent heating and mass motions. In low gravity stars, evidence is found for relatively fast (approximately 200 km s(exp -1)), warm winds with rapid acceleration occurring in the chromosphere. In some cases outflows commensurate with stellar escape velocities are present. Our current understanding of cool star winds will be reviewed including the implications of stellar observations for identification of atmospheric heating and acceleration processes.
Guide star probabilities
Soneira, R. M.; Bahcall, J. N.
Probabilities are calculated for acquiring suitable guide stars (GS) with the fine guidance system (FGS) of the space telescope. A number of the considerations and techniques described are also relevant for other space astronomy missions. The constraints of the FGS are reviewed. The available data on bright star densities are summarized and a previous error in the literature is corrected. Separate analytic and Monte Carlo calculations of the probabilities are described. A simulation of space telescope pointing is carried out using the Weistrop north galactic pole catalog of bright stars. Sufficient information is presented so that the probabilities of acquisition can be estimated as a function of position in the sky. The probability of acquiring suitable guide stars is greatly increased if the FGS can allow an appreciable difference between the (bright) primary GS limiting magnitude and the (fainter) secondary GS limiting magnitude.
Cataclysmic Variable Stars
Hellier, Coel
Cataclysmic variable stars are the most variable stars in the night sky, fluctuating in brightness continually on timescales from seconds to hours to weeks to years. The changes can be recorded using amateur telescopes, yet are also the subject of intensive study by professional astronomers. That study has led to an understanding of cataclysmic variables as binary stars, orbiting so closely that material transfers from one star to the other. The resulting process of accretion is one of the most important in astrophysics. This book presents the first account of cataclysmic variables at an introductory level. Assuming no previous knowledge of the field, it explains the basic principles underlying the variability, while providing an extensive compilation of cataclysmic variable light curves. Aimed at amateur astronomers, undergraduates, and researchers, the main text is accessible to those with no mathematical background, while supplementary boxes present technical details and equations.
Stellar Parameters and Radial Velocities of Hot Stars in the Carina Nebula
Hanes, Richard J.; McSwain, M. Virginia; Povich, Matthew S.
The Carina Nebula is an active star-forming region in the southern sky that is of particular interest due to the presence of a large number of massive stars in a wide array of evolutionary stages. Here, we present the results of the spectroscopic analysis of 82 B-type stars and 33 O-type stars that were observed in 2013 and 2014. For 82 B-type stars without line blending, we fit model spectra from the Tlusty BSTAR2006 grid to the observed profiles of Hγ and He λλ4026, 4388, and 4471 to measure the effective temperatures, surface gravities, and projected rotational velocities. We also measure the masses, ages, radii, bolometric luminosities, and distances of these stars. From the radial velocities measured in our sample, we find 31 single lined spectroscopic binary candidates. We find a high dispersion of radial velocities among our sample stars, and we argue that the Carina Nebula stellar population has not yet relaxed and become virialized.
HST/STIS ULTRAVIOLET SPECTROSCOPY OF THE COMPONENTS OF THE MASSIVE TRIPLE STAR δ ORI A
Richardson, Noel D.; Moffat, Anthony F. J.; Gull, Theodore R.
The multiple star system of δ Orionis is one of the closest examples of a system containing a luminous O-type, bright giant star (component Aa1). It is often used as a spectral-type standard and has the highest observed X-ray flux of any hot-star binary. The main component Aa1 is orbited by two lower mass stars, faint Aa2 in a 5.7 day eclipsing binary, and Ab, an astrometric companion with an estimated period of 346 years. Generally the flux from all three stars is recorded in ground-based spectroscopy, and the spectral decomposition of the components has proved difficult. Here we presentmore » Hubble Space Telescope/Space Telescope Imaging Spectrograph ultraviolet spectroscopy of δ Ori A that provides us with spatially separated spectra of Aa and Ab for the first time. We measured radial velocities for Aa1 and Ab in two observations made near the velocity extrema of Aa1. We show tentative evidence for the detection of the Aa2 component in cross-correlation functions of the observed and model spectra. We discuss the appearance of the UV spectra of Aa1 and Ab with reference to model spectra. Both stars have similar effective temperatures, but Ab is fainter and is a rapid rotator. The results will help in the interpretation of ground-based spectroscopy and in understanding the physical and evolutionary parameters of these massive stars.« less
Catch a Star 2008!
ESO and the European Association for Astronomy Education have just launched the 2008 edition of 'Catch a Star', their international astronomy competition for school students. Now in its sixth year, the competition offers students the chance to win a once-in-a-lifetime trip to ESO's flagship observatory in Chile, as well as many other prizes. CAS logo The competition includes separate categories - 'Catch a Star Researchers' and 'Catch a Star Adventurers' - to ensure that every student, whatever their level, has the chance to enter and win exciting prizes. In teams, students investigate an astronomical topic of their choice and write a report about it. An important part of the project for 'Catch a Star Researchers' is to think about how ESO's telescopes such as the Very Large Telescope (VLT) or future telescopes such as the Atacama Large Millimeter/submillimeter Array (ALMA) and the European Extremely Large Telescope (E-ELT) could contribute to investigations of the topic. Students may also include practical activities such as observations or experiments. For the artistically minded, 'Catch a Star' also offers an artwork competition, 'Catch a Star Artists'. Last year, hundreds of students from across Europe and beyond took part in 'Catch a Star', submitting astronomical projects and artwork. "'Catch a Star' gets students thinking about the wonders of the Universe and the science of astronomy, with a chance of winning great prizes. It's easy to take part, whether by writing about astronomy or creating astronomically inspired artwork," said Douglas Pierce-Price, Education Officer at ESO. As well as the top prize - a trip to ESO's Very Large Telescope in Chile - visits to observatories in Austria and Spain, and many other prizes, can also be won. 'Catch a Star Researchers' winners will be chosen by an international jury, and 'Catch a Star Adventurers' will be awarded further prizes by lottery. Entries for 'Catch a Star Artists' will be displayed on the web and winners
Sounds of a Star
Acoustic Oscillations in Solar-Twin "Alpha Cen A" Observed from La Silla by Swiss Team Summary Sound waves running through a star can help astronomers reveal its inner properties. This particular branch of modern astrophysics is known as "asteroseismology" . In the case of our Sun, the brightest star in the sky, such waves have been observed since some time, and have greatly improved our knowledge about what is going on inside. However, because they are much fainter, it has turned out to be very difficult to detect similar waves in other stars. Nevertheless, tiny oscillations in a solar-twin star have now been unambiguously detected by Swiss astronomers François Bouchy and Fabien Carrier from the Geneva Observatory, using the CORALIE spectrometer on the Swiss 1.2-m Leonard Euler telescope at the ESO La Silla Observatory. This telescope is mostly used for discovering exoplanets (see ESO PR 07/01 ). The star Alpha Centauri A is the nearest star visible to the naked eye, at a distance of a little more than 4 light-years. The new measurements show that it pulsates with a 7-minute cycle, very similar to what is observed in the Sun . Asteroseismology for Sun-like stars is likely to become an important probe of stellar theory in the near future. The state-of-the-art HARPS spectrograph , to be mounted on the ESO 3.6-m telescope at La Silla, will be able to search for oscillations in stars that are 100 times fainter than those for which such demanding observations are possible with CORALIE. PR Photo 23a/01 : Oscillations in a solar-like star (schematic picture). PR Photo 23b/01 : Acoustic spectrum of Alpha Centauri A , as observed with CORALIE. Asteroseismology: listening to the stars ESO PR Photo 23a/01 ESO PR Photo 23a/01 [Preview - JPEG: 357 x 400 pix - 96k] [Normal - JPEG: 713 x 800 pix - 256k] [HiRes - JPEG: 2673 x 3000 pix - 2.1Mb Caption : PR Photo 23a/01 is a graphical representation of resonating acoustic waves in the interior of a solar-like star. Red and blue
Dating the Stars Next Door: Ages and Coronal X-Ray Activities of Local K-Type Stars
Katynski, Marcus; Guinan, Edward F.; Engle, Scott G.
Age is one of the most difficult (but important) basic stellar physical property to determine. One possible means to estimate stellar age is from rotational period; it is known that as cool stars age, they lose angular momentum from magnetic braking and slow-down. Thus, good Rotation-Age relationships exist, which are calibrated with stars possessing reliable ages from: evolutionary tracks and/or memberships in clusters/moving groups or binary star systems. Further, ages of older stars can be estimated from (low) metal abundances and kinematics (high space motions). More recently, age determinations from asteroseismology are also becoming more reliable. Except for the many G, K, M stars in the Kepler/K2 fields, rotational periods are difficult to measure photometrically for older, less active stars since star spots and active regions are smaller & less prominent. Thus measuring the coronal X-ray activity of a star is an appealing alternative. Coronal X-ray emission is generated by the stellar dynamo, and so is directly related to the stars' rotation (and age). Measurement of X-ray fluxes (or upper limits) have been made for most of the nearby stars (within ~20 pc) with data available in the HEASARC archives. During the 1990's the ROSAT X-Ray Satellite carried out an all-sky survey of thousands of X-ray sources, including hundreds of nearby stars, producing a large archival database. Using these and other available X-ray data from XMM-Newton & Chandra, we explore the relation between coronal X-ray activity and stellar age of all stars within 10 pc (32.6 LY), with special emphasis on dK and early dM stars that make up ~85% of the sample. Here we report the progress made in determination the ages these nearby stars. We focused on nearby dK-stars, due to their long lifetimes (>20 Gyr) and habitable zones that lie ~0.5 -1.5 AU from their host stars. They appear to be ideal candidates for hosting potentially habitable planets, making them interesting targets. We present
Chaotic Star Birth
[figure removed for brevity, see original site] [figure removed for brevity, see original site] Click on the image for Poster VersionClick on the image for IRAS 4B Inset
Located 1,000 light years from Earth in the constellation Perseus, a reflection nebula called NGC 1333 epitomizes the beautiful chaos of a dense group of stars being born. Most of the visible light from the young stars in this region is obscured by the dense, dusty cloud in which they formed. With NASA's Spitzer Space Telescope, scientists can detect the infrared light from these objects. This allows a look through the dust to gain a more detailed understanding of how stars like our sun begin their lives.
The young stars in NGC 1333 do not form a single cluster, but are split between two sub-groups. One group is to the north near the nebula shown as red in the image. The other group is south, where the features shown in yellow and green abound in the densest part of the natal gas cloud. With the sharp infrared eyes of Spitzer, scientists can detect and characterize the warm and dusty disks of material that surround forming stars. By looking for differences in the disk properties between the two subgroups, they hope to find hints of the star and planet formation history of this region.
The knotty yellow-green features located in the lower portion of the image are glowing shock fronts where jets of material, spewed from extremely young embryonic stars, are plowing into the cold, dense gas nearby. The sheer number of separate jets that appear in this region is unprecedented. This leads scientists to believe that by stirring up the cold gas, the jets may contribute to the eventual dispersal of the gas cloud, preventing more stars from forming in NGC 1333.
In contrast, the upper portion of the image is dominated by the infrared light from warm dust, shown as red.
Recent highlights from STAR
Zha, Wangmei
The Solenoidal Tracker at RHIC (STAR) experiment takes advantage of its excellent tracking and particle identification capabilities at mid-rapidity to explore the properties of strongly interacting QCD matter created in heavy-ion collisions at RHIC. The STAR collaboration presented 7 parallel and 2 plenary talks at Strangeness in Quark Matter 2017 and covered various topics including heavy flavor measurements, bulk observables, electro-magnetic probes and the upgrade program. This paper highlights some of the selected results.
Hughes, D.; Murdin, P.
The biblical Star of Bethlehem, which heralded the birth of Jesus Christ, is only mentioned in the Gospel of St Matthew 2. The astrologically significant 7 bc triple conjunction of Jupiter and Saturn in the constellation of Pisces is the most likely candidate, although a comet/nova in 5 bc and a comet in 4 bc cannot be ruled out. There is also the possibility that the star was simply fictitious....
Bubbly Little Star
In this processed Spitzer Space Telescope image, baby star HH 46/47 can be seen blowing two massive 'bubbles.' The star is 1,140 light-years away from Earth.
The infant star can be seen as a white spot toward the center of the Spitzer image. The two bubbles are shown as hollow elliptical shells of bluish-green material extending from the star. Wisps of green in the image reveal warm molecular hydrogen gas, while the bluish tints are formed by starlight scattered by surrounding dust.
These bubbles formed when powerful jets of gas, traveling at 200 to 300 kilometers per second, or about 120 to 190 miles per second, smashed into the cosmic cloud of gas and dust that surrounds HH 46/47. The red specks at the end of each bubble show the presence of hot sulfur and iron gas where the star's narrow jets are currently crashing head-on into the cosmic cloud's gas and dust material.
Whenever astronomers observe a star, or snap a stellar portrait, through the lens of any telescope, they know that what they are seeing is slightly blurred. To clear up the blurring in Spitzer images, astronomers at the Jet Propulsion Laboratory developed an image processing technique for Spitzer called Hi-Res deconvolution.
This process reduces blurring and makes the image sharper and cleaner, enabling astronomers to see the emissions around forming stars in greater detail. When scientists applied this image processing technique to the Spitzer image of HH 46/47, they were able to see winds from the star and jets of gas that are carving the celestial bubbles.
This infrared image is a three-color composite, with data at 3.6 microns represented in blue, 4.5 and 5.8 microns shown in green, and 24 microns represented as red.
Astro STARS Camp
Tom Nicolaides, an aerospace technologist in the Engineering & Test Directorate at Stennis Space Center, looks on as 2011 Astro STARS participants take turns gazing at the sun through a special telescope. The sun-gazing activity was part of the Astro STARS (Spaceflight, Technology, Astronomy & Robotics at Stennis) camp for 13-to-15-year-olds June 27 - July 1. The weeklong science and technology camp is held each year onsite at the rocket engine test facility.
Mimetic compact stars
Momeni, D.; Moraes, P. H. R. S.; Gholizade, H.; Myrzakulov, R.
Modified gravity models have been constantly proposed with the purpose of evading some standard gravity shortcomings. Recently proposed by Chamseddine and Mukhanov, the Mimetic Gravity arises as an optimistic alternative. Our purpose in this work is to derive Tolman-Oppenheimer-Volkoff equations and solutions for such a gravity theory. We solve them numerically for quark star and neutron star cases. The results are carefully discussed.
Barium Stars: Theoretical Interpretation
Husti, Laura; Gallino, Roberto; Bisterzo, Sara; Straniero, Oscar; Cristallo, Sergio
Barium stars are extrinsic Asymptotic Giant Branch (AGB) stars. They present the s-enhancement characteristic for AGB and post-AGB stars, but are in an earlier evolutionary stage (main sequence dwarfs, subgiants, red giants). They are believed to form in binary systems, where a more massive companion evolved faster, produced the s-elements during its AGB phase, polluted the present barium star through stellar winds and became a white dwarf. The samples of barium stars of Allen & Barbuy (2006) and of Smiljanic et al. (2007) are analysed here. Spectra of both samples were obtained at high-resolution and high S/N. We compare these observations with AGB nucleosynthesis models using different initial masses and a spread of 13C-pocket efficiencies. Once a consistent solution is found for the whole elemental distribution of abundances, a proper dilution factor is applied. This dilution is explained by the fact that the s-rich material transferred from the AGB to the nowadays observed stars is mixed with the envelope of the accretor. We also analyse the mass transfer process, and obtain the wind velocity for giants and subgiants with known orbital period. We find evidence that thermohaline mixing is acting inside main sequence dwarfs and we present a method for estimating its depth.
Multiplicity of Massive Stars
Zinnecker, Hans
We review the multiplicity of massive stars by compiling the abstracts of the most relevant papers in the field. We start by discussing the massive stars in the Orion Trapezium Cluster and in other Galactic young clusters and OB associations, and end with the R136 cluster in the LMC. The multiplicity of field O-stars and runaway OB stars is also reviewed. The results of both visual and spectroscopic surveys are presented, as well as data for eclipsing systems. Among the latter, we find the most massive known binary system WR20a, with two ~,80M_⊙ components in a 3 day orbit. Some 80% of the wide visual binaries in stellar associations are in fact hierarchical triple systems, where typically the more massive of the binary components is itself a spectroscopic or even eclipsing binary pair. The multiplicity (number of companions) of massive star primaries is significantly higher than for low-mass solar-type primaries or for young low-mass T Tauri stars. There is also a striking preponderance of very close nearly equal mass binary systems (the origin of which has recently been explained in an accretion scenario). Finally, we offer a new idea as to the origin of massive Trapezium systems, frequently found in the centers of dense young clusters.
Infant stars are glowing gloriously in this infrared image of the Serpens star-forming region, captured by NASA's Spitzer Space Telescope.
The reddish-pink dots are baby stars deeply embedded in the cosmic cloud of gas and dust that collapsed to create it. A dusty disk of cosmic debris, or 'protoplanetary disk,' that may eventually form planets, surrounds the infant stars.
Wisps of green throughout the image indicate the presence of carbon rich molecules called polycyclic aromatic hydrocarbons. On Earth, these molecules can be found on charred barbecue grills and in automobile exhaust. Blue specks sprinkled throughout the image are background stars in our Milky Way galaxy.
The Serpens star-forming region is located approximately 848 light-years away in the Serpens constellation.
The image is a three-channel, false-color composite, where emission at 4.5 microns is blue, emission at 8.0 microns is green, and 24 micron emission is red.
Young Stars with SALT
Riedel, Adric R.; Alam, Munazza K.; Rice, Emily L.
We present a spectroscopic and kinematic analysis of 79 nearby M dwarfs in 77 systems. All of these dwarfs are low-proper-motion southern hemisphere objects and were identified in a nearby star survey with a demonstrated sensitivity to young stars. Using low-resolution optical spectroscopy from the Red Side Spectrograph on the South African Large Telescope, we have determined radial velocities, H-alpha, lithium 6708 Å, and potassium 7699 Å equivalent widths linked to age and activity, and spectral types for all of our targets. Combined with astrometric information from literature sources, we identify 44 young stars. Eighteen are previously known members ofmore » moving groups within 100 pc of the Sun. Twelve are new members, including one member of the TW Hydra moving group, one member of the 32 Orionis moving group, 9 members of Tucana-Horologium, one member of Argus, and two new members of AB Doradus. We also find 14 young star systems that are not members of any known groups. The remaining 33 star systems do not appear to be young. This appears to be evidence of a new population of nearby young stars not related to the known nearby young moving groups.« less
Hot Subluminous Stars
Heber, U.
Hot subluminous stars of spectral type B and O are core helium-burning stars at the blue end of the horizontal branch or have evolved even beyond that stage. Most hot subdwarf stars are chemically highly peculiar and provide a laboratory to study diffusion processes that cause these anomalies. The most obvious anomaly lies with helium, which may be a trace element in the atmosphere of some stars (sdB, sdO) while it may be the dominant species in others (He-sdB, He-sdO). Strikingly, the distribution in the Hertzsprung-Russell diagram of He-rich versus He-poor hot subdwarf stars of the globular clusters ω Cen and NGC 2808 differ from that of their field counterparts. The metal-abundance patterns of hot subdwarfs are typically characterized by strong deficiencies of some lighter elements as well as large enrichments of heavy elements. A large fraction of sdB stars are found in close binaries with white dwarf or very low-mass main sequence companions, which must have gone through a common-envelope (CE) phase of evolution. Because the binaries are detached they provide a clean-cut laboratory to study this important but yet poorly understood phase of stellar evolution. Hot subdwarf binaries with sufficiently massive white dwarf companions are viable candidate progenitors of type Ia supernovae both in the double degenerate as well as in the single degenerate scenario as helium donors for double detonation supernovae. The hyper-velocity He-sdO star US 708 may be the surviving donor of such a double detonation supernova. Substellar companions to sdB stars have also been found. For HW Vir systems the companion mass distribution extends from the stellar into the brown dwarf regime. A giant planet to the acoustic-mode pulsator V391 Peg was the first discovery of a planet that survived the red giant evolution of its host star. Evidence for Earth-size planets to two pulsating sdB stars have been reported and circumbinary giant planets or brown dwarfs have been found around HW
A 30Â kpc CHAIN OF ''BEADS ON A STRING'' STAR FORMATION BETWEEN TWO MERGING EARLY TYPE GALAXIES IN THE CORE OF A STRONG-LENSING GALAXY CLUSTER
Tremblay, Grant R.; Davis, Timothy A.; Gladders, Michael D.
New Hubble Space Telescope ultraviolet and optical imaging of the strong-lensing galaxy cluster SDSS J1531+3414 (z = 0.335) reveals two centrally dominant elliptical galaxies participating in an ongoing major merger. The interaction is at least somewhat rich in cool gas, as the merger is associated with a complex network of 19 massive superclusters of young stars (or small tidal dwarf galaxies) separated by ∼1 kpc in projection from one another, combining to an estimated total star formation rate of ∼5 M {sub ☉} yr{sup –1}. The resolved young stellar superclusters are threaded by narrow Hα, [O II], and blue excess filaments arrangedmore » in a network spanning ∼27 kpc across the two merging galaxies. This morphology is strongly reminiscent of the well-known ''beads on a string'' mode of star formation observed on kiloparsec scales in the arms of spiral galaxies, resonance rings, and in tidal tails between interacting galaxies. Nevertheless, the arrangement of this star formation relative to the nuclei of the two galaxies is difficult to interpret in a dynamical sense, as no known ''beads on a string'' systems associated with kiloparsec-scale tidal interactions exhibit such lopsided morphology relative to the merger participants. In this Letter, we present the images and follow-up spectroscopy and discuss possible physical interpretations for the unique arrangement of the young stellar clusters. While we suggest that this morphology is likely to be dynamically short-lived, a more quantitative understanding awaits necessary multiwavelength follow-up, including optical integral field spectroscopy, ALMA submillimeter interferometry, and Chandra X-ray imaging.« less
Habitable zones around main sequence stars.
Kasting, J F; Whitmire, D P; Reynolds, R T
remain habitable and on whether a planet that is initially frozen can be thawed by modest increases in stellar luminosity. For a specified period of habitability, CHZs around K and M stars are wider (in log distance) than for our Sun because these stars evolve more slowly. Planets orbiting late K stars and M stars may not be habitable, however, b ecause they can become trapped in synchronous rotation as a consequence of tidal damping. F stars have narrower (log distance) CHZ's than our Sun because they evolve more rapidly. Our results suggest that mid-to-early K stars should be considered along with G stars as optimal candidates in the search for extraterrestrial life.
A robust star identification algorithm with star shortlisting
Mehta, Deval Samirbhai; Chen, Shoushun; Low, Kay Soon
A star tracker provides the most accurate attitude solution in terms of arc seconds compared to the other existing attitude sensors. When no prior attitude information is available, it operates in "Lost-In-Space (LIS)" mode. Star pattern recognition, also known as star identification algorithm, forms the most crucial part of a star tracker in the LIS mode. Recognition reliability and speed are the two most important parameters of a star pattern recognition technique. In this paper, a novel star identification algorithm with star ID shortlisting is proposed. Firstly, the star IDs are shortlisted based on worst-case patch mismatch, and later stars are identified in the image by an initial match confirmed with a running sequential angular match technique. The proposed idea is tested on 16,200 simulated star images having magnitude uncertainty, noise stars, positional deviation, and varying size of the field of view. The proposed idea is also benchmarked with the state-of-the-art star pattern recognition techniques. Finally, the real-time performance of the proposed technique is tested on the 3104 real star images captured by a star tracker SST-20S currently mounted on a satellite. The proposed technique can achieve an identification accuracy of 98% and takes only 8.2 ms for identification on real images. Simulation and real-time results depict that the proposed technique is highly robust and achieves a high speed of identification suitable for actual space applications.
Vector space methods of photometric analysis - Applications to O stars and interstellar reddening
Massa, D.; Lillie, C. F.
A multivariate vector-space formulation of photometry is developed which accounts for error propagation. An analysis of uvby and H-beta photometry of O stars is presented, with attention given to observational errors, reddening, general uvby photometry, early stars, and models of O stars. The number of observable parameters in O-star continua is investigated, the way these quantities compare with model-atmosphere predictions is considered, and an interstellar reddening law is derived. It is suggested that photospheric expansion affects the formation of the continuum in at least some O stars.
VLA observations of A and B stars with kilogauss magnetic fields
Drake, S. A.; Abbott, D. C.; Linsky, J. L.; Bieging, J. H.; Churchwell, E.
The serendipitous discovery that the star Sigma Ori E is a 3.5 mJy radio continuum source at 6 cm has stimulated a radio survey of other early-type stars with strong magnetic fields. No Ap stars have been detected of the eight observed, with typical 3-sigma upper limits of 0.5 mJy at 2 cm. Of the six Bp stars examined, only HR 1890, a helium-strong star, was detected. Possible emission mechanisms for the observed radio emission are discussed, and it is concluded that nonthermal emission seems the most plausible, on the basis of the present data.
Rotation of low-mass stars - A new probe of stellar evolution
Pinsonneault, M. H.; Kawaler, Steven D.; Demarque, P.
Models of stars of various masses and rotational parameters were developed and compared with observations of stars in open clusters of various ages in order to analyze the evolution of rotating stars from the early premain sequence to an age of 1.7 x 10 to the 9th yrs. It is shown that, for stars older than 10 to the 8th yrs and less massive than 1.1 solar mass, the surface rotation rates depend most strongly on the properties of the angular momentum loss. The trends of the currently available observations suggest that the rotation periods are a good indicator of the field-star ages.
An Introduction to the Sun and Stars
Green, Simon F.; Jones, Mark H.
Introduction; 1. Seeing the Sun; 2. The working Sun; 3. Measuring stars; 4. Comparing stars; 5. The formation of stars; 6. The main sequence life of stars; 7. The life of stars beyond the main sequence; 8. The death of stars; 9. The remnants of stars; Conclusion; Answers and comments; Appendices; Glossary; Further reading; Acknowledgements; Figure references; Index.
Hot Star Extension to the Hubble Space Telescope Stellar Spectral Library
Khan, Islam; Worthey, Guy
CCD spectra of 36 stars were obtained from the Space Telescope Imaging Spectrograph (STIS) installed in the Hubble Space Telescope (HST) using three low resolution gratings - G230LB, G430L, and G750L, combined in processing to make single, continuous spectra from 0.2 to 1.0 micrometers. These spectra will be added to the Next Generation Stellar Library (NGSL) after completing the data analysis, reduction, and the required corrections. The stars include normal O-type stars, helium-burning stars, and post-asymptotic giant branch (PAGB) stars. Difficult steps in the data reduction process were removing the cosmic rays from the raw images and defringing of the G750L spectra using fringe flats. Most stars have detectable dust extinction. To aid in analysis, synthetic spectra were generated with various effective temperatures and surface gravities. A five parameter analytic model for the dust extinction correction was adopted. The parameters were varied in order to fit especially the ultraviolet portion of the observed and comparison synthetic spectra. Cross-correlation was used to bring the spectra to a common, final, zero velocity wavelength scale. Some star temperatures obtained from fitting synthetic versus observed spectra vary significantly from literature values. The dust extinction correction parameters also varied for several stars, mostly O stars, indicating variations in dust properties for different lines of sight. Analysis of scattered light effects showed that it was significant only for our two coolest stars.Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS 5-26555.Support for this work was provided by NASA through grant number HST-GO-14141 from the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555.
The Evolution and Stability of Massive Stars
Shiode, Joshua Hajime
Massive stars are the ultimate source for nearly all the elements necessary for life. The first stars forge these elements from the sparse set of ingredients supplied by the Big Bang, and distribute enriched ashes throughout their galactic homes via their winds and explosive deaths. Subsequent generations follow suit, assembling from the enriched ashes of their predecessors. Over the last several decades, the astrophysics community has developed a sophisticated theoretical picture of the evolution of these stars, but it remains an incomplete accounting of the rich set of observations. Using state of the art models of massive stars, I have investigated the internal processes taking place throughout the life-cycles of stars spanning those from the first generation ("Population III") to the present-day ("Population I"). I will argue that early-generation stars were not highly unstable to perturbations, contrary to a host of past investigations, if a correct accounting is made for the viscous effect of convection. For later generations, those with near solar metallicity, I find that this very same convection may excite gravity-mode oscillations that produce observable brightness variations at the stellar surface when the stars are near the main sequence. If confirmed with modern high-precision monitoring experiments, like Kepler and CoRoT, the properties of observed gravity modes in massive stars could provide a direct probe of the poorly constrained physics of gravity mode excitation by convection. Finally, jumping forward in stellar evolutionary time, I propose and explore an entirely new mechanism to explain the giant eruptions observed and inferred to occur during the final phases of massive stellar evolution. This mechanism taps into the vast nuclear fusion luminosity, and accompanying convective luminosity, in the stellar core to excite waves capable of carrying a super-Eddington luminosity out to the stellar envelope. This energy transfer from the core to the
Ultraviolet spectrophotometry from Gemini 11 of stars in Orion
Morgan, T. H.; Spear, G. G.; Kondo, Y.; Henize, K. G.
Ultraviolet spectrophotometry in the wavelength region 2600-3600 A is reported for the bright early-type stars beta, eta, gamma, delta, iota, epsilon, sigma, zeta, and kappa Ori. The results are in good agreement with other observations, and, with the possible exception of the supergiants, are in good agreement with recent line-blanketed model atmospheres. There is evidence that the supergiants possess a small ultraviolet deficiency shortward of 3000 A relative to main-sequence stars of similar spectral type. The most extreme example of this phenomenon is the star kappa Ori.
Models of symbiotic stars
Friedjung, Michael
One of the most important features of symbiotic stars is the coexistence of a cool spectral component that is apparently very similar to the spectrum of a cool giant, with at least one hot continuum, and emission lines from very different stages of ionization. The cool component dominates the infrared spectrum of S-type symbiotics; it tends to be veiled in this wavelength range by what appears to be excess emission in D-type symbiotics, this excess usually being attributed to circumstellar dust. The hot continuum (or continua) dominates the ultraviolet. X-rays have sometimes also been observed. Another important feature of symbiotic stars that needs to be explained is the variability. Different forms occur, some variability being periodic. This type of variability can, in a few cases, strongly suggest the presence of eclipses of a binary system. One of the most characteristic forms of variability is that characterizing the active phases. This basic form of variation is traditionally associated in the optical with the veiling of the cool spectrum and the disappearance of high-ionization emission lines, the latter progressively appearing (in classical cases, reappearing) later. Such spectral changes recall those of novae, but spectroscopic signatures of the high-ejection velocities observed for novae are not usually detected in symbiotic stars. However, the light curves of the 'symbiotic nova' subclass recall those of novae. We may also mention in this connection that radio observations (or, in a few cases, optical observations) of nebulae indicate ejection from symbiotic stars, with deviations from spherical symmetry. We shall give a historical overview of the proposed models for symbiotic stars and make a critical analysis in the light of the observations of symbiotic stars. We describe the empirical approach to models and use the observational data to diagnose the physical conditions in the symbiotics stars. Finally, we compare the results of this empirical
Hamann, Wolf-Rainer; Sander, Andreas; Todt, Helge
Nearly 150 years ago, the French astronomers Charles Wolf and Georges Rayet described stars with very conspicuous spectra that are dominated by bright and broad emission lines. Meanwhile termed Wolf-Rayet Stars after their discoverers, those objects turned out to represent important stages in the life of massive stars. As the first conference in a long time that was specifically dedicated to Wolf-Rayet stars, an international workshop was held in Potsdam, Germany, from 1.-5. June 2015. About 100 participants, comprising most of the leading experts in the field as well as as many young scientists, gathered for one week of extensive scientific exchange and discussions. Considerable progress has been reported throughout, e.g. on finding such stars, modeling and analyzing their spectra, understanding their evolutionary context, and studying their circumstellar nebulae. While some major questions regarding Wolf-Rayet stars still remain open 150 years after their discovery, it is clear today that these objects are not just interesting stars as such, but also keystones in the evolution of galaxies. These proceedings summarize the talks and posters presented at the Potsdam Wolf-Rayet workshop. Moreover, they also include the questions, comments, and discussions emerging after each talk, thereby giving a rare overview not only about the research, but also about the current debates and unknowns in the field. The Scientific Organizing Committee (SOC) included Alceste Bonanos (Athens), Paul Crowther (Sheffield), John Eldridge (Auckland), Wolf-Rainer Hamann (Potsdam, Chair), John Hillier (Pittsburgh), Claus Leitherer (Baltimore), Philip Massey (Flagstaff), George Meynet (Geneva), Tony Moffat (Montreal), Nicole St-Louis (Montreal), and Dany Vanbeveren (Brussels).
Low-Metallicity Star Formation: From the First Stars to Dwarf Galaxies
Hunt, Leslie K.; Madden, Suzanne C.; Schneider, Raffaella
Preface; SOC and LOC; Participants; Life at the conference; Conference photo; Session I. Population III and Metal-Free Star Formation: 1. Open questions in the study of population III star formation S. C. O. Glover, P. C. Clark, T. H. Greif, J. L. Johnson, V. Bromm, R. S. Klessen and A. Stacy; 2. Protostar formation in the early universe Naoki Yoshida; 3. Population III.1 stars: formation, feedback and evolution of the IMF Jonathan C. Tan; 4. The formation of the first galaxies and the transition to low-mass star formation T. H. Greif, D. R. G. Schleicher, J. L. Johnson, A.-K. Jappsen, R. S. Klessen, P. C. Clark, S. C. O. Glover, A. Stacy and V. Bromm; 5. Low-metallicity star formation: the characteristic mass and upper mass limit Kazuyuki Omukai; 6. Dark stars: dark matter in the first stars leads to a new phase of stellar evolution Katherine Freese, Douglas Spolyar, Anthony Aguirre, Peter Bodenheimer, Paolo Gondolo, J. A. Sellwood and Naoki Yoshida; 7. Effects of dark matter annihilation on the first stars F. Iocco, A. Bressan, E. Ripamonti, R. Schneider, A. Ferrara and P. Marigo; 8. Searching for Pop III stars and galaxies at high redshift Daniel Schaerer; 9. The search for population III stars Sperello di Serego Alighieri, Jaron Kurk, Benedetta Ciardi, Andrea Cimatti, Emanuele Daddi and Andrea Ferrara; 10. Observational search for population III stars in high-redshift galaxies Tohru Nagao; Session II. Metal Enrichment, Chemical Evolution, and Feedback: 11. Cosmic metal enrichment Andrea Ferrara; 12. Insights into the origin of the galaxy mass-metallicity relation Henry Lee, Eric F. Bell and Rachel S. Somerville; 13. LSD and AMAZE: the mass-metallicity relation at z > 3 F. Mannucci and R. Maiolino; 14. Three modes of metal-enriched star formation at high redshift Britton D. Smith, Matthew J. Turk, Steinn Sigurdsson, Brian W. O'Shea and Michael L. Norman; 15. Primordial supernovae and the assembly of the first galaxies Daniel Whalen, Bob Van Veelen, Brian W. O
The HOSTS Survey—Exozodiacal Dust Measurements for 30 Stars
Ertel, S.; Defrère, D.; Hinz, P.; Mennesson, B.; Kennedy, G. M.; Danchi, W. C.; Gelino, C.; Hill, J. M.; Hoffmann, W. F.; Rieke, G.; Shannon, A.; Spalding, E.; Stone, J. M.; Vaz, A.; Weinberger, A. J.; Willems, P.; Absil, O.; Arbo, P.; Bailey, V. P.; Beichman, C.; Bryden, G.; Downey, E. C.; Durney, O.; Esposito, S.; Gaspar, A.; Grenz, P.; Haniff, C. A.; Leisenring, J. M.; Marion, L.; McMahon, T. J.; Millan-Gabet, R.; Montoya, M.; Morzinski, K. M.; Pinna, E.; Power, J.; Puglisi, A.; Roberge, A.; Serabyn, E.; Skemer, A. J.; Stapelfeldt, K.; Su, K. Y. L.; Vaitheeswaran, V.; Wyatt, M. C.
The Hunt for Observable Signatures of Terrestrial Systems survey searches for dust near the habitable zones (HZs) around nearby, bright main-sequence stars. We use nulling interferometry in the N band to suppress the bright stellar light and to probe for low levels of HZ dust around the 30 stars observed so far. Our overall detection rate is 18%, including four new detections, among which are the first three around Sun-like stars and the first two around stars without any previously known circumstellar dust. The inferred occurrence rates are comparable for early-type and Sun-like stars, but decrease from {60}-21+16% for stars with previously detected cold dust to {8}-3+10% for stars without such excess, confirming earlier results at higher sensitivity. For completed observations on individual stars, our sensitivity is five to ten times better than previous results. Assuming a lognormal excess luminosity function, we put upper limits on the median HZ dust level of 13 zodis (95% confidence) for a sample of stars without cold dust and of 26 zodis when focusing on Sun-like stars without cold dust. However, our data suggest that a more complex luminosity function may be more appropriate. For stars without detectable Large Binocular Telescope Interferometer (LBTI) excess, our upper limits are almost reduced by a factor of two, demonstrating the strength of LBTI target vetting for future exo-Earth imaging missions. Our statistics are limited so far, and extending the survey is critical to informing the design of future exo-Earth imaging surveys.
Massive Stars in the W33 Giant Molecular Complex
Messineo, Maria; Clark, J. Simon; Figer, Donald F.; Kudritzki, Rolf-Peter; Najarro, Francisco; Rich, R. Michael; Menten, Karl M.; Ivanov, Valentin D.; Valenti, Elena; Trombley, Christine; Chen, C.-H. Rosie; Davies, Ben
Rich in H ii regions, giant molecular clouds are natural laboratories to study massive stars and sequential star formation. The Galactic star-forming complex W33 is located at l=˜ 12\\buildrel{\\circ}\\over{.} 8 and at a distance of 2.4 kpc and has a size of ≈ 10 pc and a total mass of ≈ (0.8-8.0) × {{10}5} M ⊙ . The integrated radio and IR luminosity of W33—when combined with the direct detection of methanol masers, the protostellar object W33A, and the protocluster embedded within the radio source W33 main—mark the region as a site of vigorous ongoing star formation. In order to assess the long-term star formation history, we performed an infrared spectroscopic search for massive stars, detecting for the first time 14 early-type stars, including one WN6 star and four O4-7 stars. The distribution of spectral types suggests that this population formed during the past ˜2-4 Myr, while the absence of red supergiants precludes extensive star formation at ages 6-30 Myr. This activity appears distributed throughout the region and does not appear to have yielded the dense stellar clusters that characterize other star-forming complexes such as Carina and G305. Instead, we anticipate that W33 will eventually evolve into a loose stellar aggregate, with Cyg OB2 serving as a useful, albeit richer and more massive, comparator. Given recent distance estimates, and despite a remarkably similar stellar population, the rich cluster Cl 1813-178 located on the northwest edge of W33 does not appear to be physically associated with W33.
The Beginning of Variable star astronomy in Hungary
Zsoldos, Endre
Variable star astronomy began in Hungary as elsewhere: new objects have been recognized in the sky. Comets appeared in 16th - 17th century chronicles. The first mention of the new star of 1572 seems to be the "Prognosticon" of Wilhelm Misocacus, printed in 1578. New stars were discussed in the 17th century by Jesuits as well as Protestants. The work of Jacob Schnitzler is especially interesting from this point. The Cartesians dealt with new stars with less enthusiasm, they hardly mentioned them. The beginning of the 19th century saw the development of science in Hungarian, variable stars, however, were left out. The birth of variable star astronomy might be linked to the Ógyalla Observatory, originally a private observatory of Miklós Konkoly Thege. The 1885 supernova in the Andromeda Nebula were observed there, as well as the spectra of a few interesting variable stars. Theoretical astrophysics also has its beginnings in Ógyalla through the work of Radó Kövesligethy. Professional variable star astronomy started here in the early 20th century through the work of Antal Tass
Massive runaway stars in the Small Magellanic Cloud
Gvaramadze, V. V.; Pflamm-Altenburg, J.; Kroupa, P.
Using archival Spitzer Space Telescope data, we identified for the first time a dozen runaway OB stars in the Small Magellanic Cloud (SMC) through the detection of their bow shocks. The geometry of detected bow shocks allows us to infer the direction of motion of the associated stars and to determine their possible parent clusters and associations. One of the identified runaway stars, AzV 471, was already known as a high-velocity star on the basis of its high peculiar radial velocity, which is offset by ≃ 40 km s-1 from the local systemic velocity. We discuss implications of our findings for the problem of the origin of field OB stars. Several of the bow shock-producing stars are found in the confines of associations, suggesting that these may be "alien� stars contributing to the age spread observed for some young stellar systems. We also report the discovery of a kidney-shaped nebula attached to the early WN-type star SMC-WR3 (AzV 60a). We interpreted this nebula as an interstellar structure created owing to the interaction between the stellar wind and the ambient interstellar medium.
Very massive runaway stars from three-body encounters
Gvaramadze, Vasilii V.; Gualandris, Alessia
Very massive stars preferentially reside in the cores of their parent clusters and form binary or multiple systems. We study the role of tight very massive binaries in the origin of the field population of very massive stars. We performed numerical simulations of dynamical encounters between single (massive) stars and a very massive binary with parameters similar to those of the most massive known Galactic binaries, WR 20a and NGC 3603-A1. We found that these three-body encounters could be responsible for the origin of high peculiar velocities (≥70 km s-1) observed for some very massive (≥60-70 M⊙) runaway stars in the Milky Way and the Large Magellanic Cloud (e.g. λ Cep, BD+43°3654, Sk -67°22, BI 237, 30 Dor 016), which can hardly be explained within the framework of the binary-supernova scenario. The production of high-velocity massive stars via three-body encounters is accompanied by the recoil of the binary in the opposite direction to the ejected star. We show that the relative position of the very massive binary R145 and the runaway early B-type star Sk-69°206 on the sky is consistent with the possibility that both objects were ejected from the central cluster, R136, of the star-forming region 30 Doradus via the same dynamical event - a three-body encounter.
STEM and the Evolution of the Astronomical Star Party
Day, B. H.; Munive, P.; Franco, J.; Jones, A. P.; Shaner, A. J.; Buxner, S.; Bleacher, L.
The astronomical star party has long been a powerful and effective way to engage the public and enhance cohesiveness within the amateur astronomy community. Early star parties tended to be strictly small, local events. But with improvements in transportation, larger regional star parties became popular. These advanced the considerable capabilities for citizen science in the amateur community, shared technology and engineering innovations in the field of telescope making, and refined numerous mathematical techniques in areas such instrument design and ephemeris generation, covering the full breadth of STEM. Advancements in astrophotography showcased at these events brought the star party from STEM to STEAM. Now, the advent of social media, web streaming, and virtual presence has facilitated the phenomenon of very large, networked star parties with international scope. These mega star parties take public engagement to a new, far greater levels, giving a vastly larger and more diverse public the opportunity to directly participate in exciting first-hand STEM activities. This presentation will recount the evolution of the star party and will focus on two examples of large, multinational, networked star parties, International Observe the Moon Night and Noche de las Estrellas. We will look at lessons learned and ways to participate.
Random forest classification of stars in the Galactic Centre
Plewa, P. M.
Near-infrared high-angular resolution imaging observations of the Milky Way's nuclear star cluster have revealed all luminous members of the existing stellar population within the central parsec. Generally, these stars are either evolved late-type giants or massive young, early-type stars. We revisit the problem of stellar classification based on intermediate-band photometry in the K band, with the primary aim of identifying faint early-type candidate stars in the extended vicinity of the central massive black hole. A random forest classifier, trained on a subsample of spectroscopically identified stars, performs similarly well as competitive methods (F1 = 0.85), without involving any model of stellar spectral energy distributions. Advantages of using such a machine-trained classifier are a minimum of required calibration effort, a predictive accuracy expected to improve as more training data become available, and the ease of application to future, larger data sets. By applying this classifier to archive data, we are also able to reproduce the results of previous studies of the spatial distribution and the K-band luminosity function of both the early- and late-type stars.
Hubble Sees a Star Set to Explode
Floating at the center of this new Hubble image is a lidless purple eye, staring back at us through space. This ethereal object, known officially as [SBW2007] 1 but sometimes nicknamed SBW1, is a nebula with a giant star at its center. The star was originally twenty times more massive than our sun, and is now encased in a swirling ring of purple gas, the remains of the distant era when it cast off its outer layers via violent pulsations and winds. But the star is not just any star; scientists say that it is destined to go supernova. Twenty-six years ago, another star with striking similarities went supernova — SN 1987A. Early Hubble images of SN 1987A show eerie similarities to SBW1. Both stars had identical rings of the same size and age, which were travelling at similar speeds; both were located in similar HII regions; and they had the same brightness. In this way SBW1 is a snapshot of SN1987a's appearance before it exploded, and unsurprisingly, astronomers love studying them together. At a distance of more than 20 000 light-years it will be safe to watch when the supernova goes off. If we are very lucky it may happen in our own lifetimes. Credit: ESA/NASA, acknowledgement: Nick Rose NASA image use policy. NASA Goddard Space Flight Center enables NASA's mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA's accomplishments by contributing compelling scientific knowledge to advance the Agency's mission. Follow us on Twitter Like us on Facebook Find us on Instagram
Origin of Neutron Stars
Brecher, K.
The origin of the concept of neutron stars can be traced to two brief, incredibly insightful publications. Work on the earlier paper by Lev Landau (Phys. Z. Sowjetunion, 1, 285, 1932) actually predated the discovery of neutrons. Nonetheless, Landau arrived at the notion of a collapsed star with the density of a nucleus (really a "nucleus star") and demonstrated (at about the same time as, and independent of, Chandrasekhar) that there is an upper mass limit for dense stellar objects of about 1.5 solar masses. Perhaps even more remarkable is the abstract of a talk presented at the December 1933 meeting of the American Physical Society published by Walter Baade and Fritz Zwicky in 1934 (Phys. Rev. 45, 138). It followed the discovery of the neutron by just over a year. Their report, which was about the same length as the present abstract: (1) invented the concept and word supernova; (2) suggested that cosmic rays are produced by supernovae; and (3) in the authors own words, proposed "with all reserve ... the view that supernovae represent the transitions from ordinary stars to neutron stars (italics), which in their final stages consist of extremely closely packed neutrons." The abstract by Baade and Zwicky probably contains the highest density of new, important (and correct) ideas in high energy astrophysics ever published in a single paper. In this talk, we will discuss some of the facts and myths surrounding these two publications.
Circulation of Stars
Boitani, P.
Since the dawn of man, contemplation of the stars has been a primary impulse in human beings, who proliferated their knowledge of the stars all over the world. Aristotle sees this as the product of primeval and perennial "wonder� which gives rise to what we call science, philosophy, and poetry. Astronomy, astrology, and star art (painting, architecture, literature, and music) go hand in hand through millennia in all cultures of the planet (and all use catasterisms to explain certain phenomena). Some of these developments are independent of each other, i.e., they take place in one culture independently of others. Some, on the other hand, are the product of the "circulation of stars.� There are two ways of looking at this. One seeks out forms, the other concentrates on the passing of specific lore from one area to another through time. The former relies on archetypes (for instance, with catasterism), the latter constitutes a historical process. In this paper I present some of the surprising ways in which the circulation of stars has occurred—from East to West, from East to the Far East, and from West to East, at times simultaneously.
VizieR Online Data Catalog: Common proper motion stars in the Kepler field (Janes, 2017)
Janes, K. A.
In a search of proper motion catalogs for common proper motion stars in the field of the Kepler spacecraft I identified 93 likely binary systems. A comparison of their rotation periods is a test of the gyrochronology concept. To find their periods I calculated the autocorrelation function (ACF) of the Kepler mission photometry for each star. In most systems for which good periods can be found, the cooler star has a longer period than the hotter component, in general agreement with models. However, there is a wide range in the gradients of lines connecting binary pairs in a period-color diagram. Furthermore, near the solar color, only a few stars have longer periods than the Sun, suggesting that they, and their cooler companions, are not much older than the Sun. In addition, there is an apparent gap at intermediate periods in the period distribution of the late K and early M stars. Either star formation in this direction has been variable, or stars evolve in period at a non-uniform rate, or some stars evolve more rapidly than others at the same mass. Finally, using the ACF as a measure of the activity level, I found that while the F, G, and early K stars become less active as their periods increase, there is no correlation between period and activity for the mid K to early M stars. (1 data file).
Adiabatic Mass Loss Model in Binary Stars
Ge, H. W.
Rapid mass transfer process in the interacting binary systems is very complicated. It relates to two basic problems in the binary star evolution, i.e., the dynamically unstable Roche-lobe overflow and the common envelope evolution. Both of the problems are very important and difficult to be modeled. In this PhD thesis, we focus on the rapid mass loss process of the donor in interacting binary systems. The application to the criterion of dynamically unstable mass transfer and the common envelope evolution are also included. Our results based on the adiabatic mass loss model could be used to improve the binary evolution theory, the binary population synthetic method, and other related aspects. We build up the adiabatic mass loss model. In this model, two approximations are included. The first one is that the energy generation and heat flow through the stellar interior can be neglected, hence the restructuring is adiabatic. The second one is that he stellar interior remains in hydrostatic equilibrium. We model this response by constructing model sequences, beginning with a donor star filling its Roche lobe at an arbitrary point in its evolution, holding its specific entropy and composition profiles fixed. These approximations are validated by the comparison with the time-dependent binary mass transfer calculations and the polytropic model for low mass zero-age main-sequence stars. In the dynamical time scale mass transfer, the adiabatic response of the donor star drives it to expand beyond its Roche lobe, leading to runaway mass transfer and the formation of a common envelope with its companion star. For donor stars with surface convection zones of any significant depth, this runaway condition is encountered early in mass transfer, if at all; but for main sequence stars with radiative envelopes, it may be encountered after a prolonged phase of thermal time scale mass transfer, so-called delayed dynamical instability. We identify the critical binary mass ratio for the
The turbulent formation of stars
Federrath, Christoph
How stars are born from clouds of gas is a rich physics problem whose solution will inform our understanding of not just stars but also planets, galaxies, and the universe itself. Star formation is stupendously inefficient. Take the Milky Way. Our galaxy contains about a billion solar masses of fresh gas available to form stars-and yet it produces only one solar mass of new stars a year. Accounting for that inefficiency is one of the biggest challenges of modern astrophysics. Why should we care about star formation? Because the process powers the evolution of galaxies and sets the initial conditions for planet formation and thus, ultimately, for life.
Four new Delta Scuti stars
Schutt, R. L.
Four new Delta Scuti stars are reported. Power, modified into amplitude, spectra, and light curves are used to determine periodicities. A complete frequency analysis is not performed due to the lack of a sufficient time base in the data. These new variables help verify the many predictions that Delta Scuti stars probably exist in prolific numbers as small amplitude variables. Two of these stars, HR 4344 and HD 107513, are possibly Am stars. If so, they are among the minority of variable stars which are also Am stars.
VizieR Online Data Catalog: Three O-type binaries photometry in LMC (Morrell+, 2014)
Morrell, N. I.; Massey, P.; Neugent, K. F.; Penny, L. R.; Gies, D. R.
We will concentrate on the presentation and discussion of our photometric and spectroscopic observations of 3 binary systems containing the earliest type components among the observed sample of 17 binaries in the LMC, namely, LMC 169782, LMC 171520, and [P93] 921. All three systems belong to the 30 Dor region, which harbors some of the most massive stars known to date (Crowther et al. 2010MNRAS.408..731C; Schnurr et al. 2009MNRAS.395..823S).Time-resolved photometry was carried out for all three systems in order to provide the light curves needed to establish periods and calculate orbital inclinations. As described in Paper I (Massey et al. 2012ApJ...748...96M), this was carried out using simple aperture photometry as opposed to point-spread-function fitting; tests showed that we obtained equally accurate results with aperture photometry, which was expected given that our targets are not overly crowded. In order to compute the observed absolute magnitudes for our targets, we have assumed a distance modulus of 18.50 (50 kpc) for the LMC following van den Bergh (2000, The Galaxies of the Local Group (Cambridge: Cambridge Univ. Press)), and we have used the intrinsic colors given by FitzGerald (1970A&A.....4..234F) and a normal reddening law with Rv = 3.1. (3 data files).
GIRAFFE Reaches towards the Stars
"First Light" of New Powerful Spectrograph at the VLT Summary The first observations of stellar spectra have just been performed with the new GIRAFFE multi-object spectrograph on the ESO Very Large Telescope (VLT) at the Paranal Observatory in Chile. This milestone event was achieved in the early morning of July 3, 2002. It signifies another important step towards the full implementation of the extremely powerful Fibre Large Array Multi-Element Spectrograph (FLAMES) , one of the main instruments for the ESO VLT. This project is co-ordinated by ESO and incorporates many complex components that have been constructed at various research institutions in Europe and Australia. The GIRAFFE spectrograph provides unique possibilities for detailed observations of the properties of individual stars located in our Milky Way galaxy ( PR 16b/02 ) as well as in other galaxies of the Local Group. PR Photo 16a/02 : A series of stellar spectra recorded by GIRAFFE during "First Light" . PR Photo 16b/02 : Details of some of these stellar spectra . FLAMES and GIRAFFE ESO PR Photo 16a/02 ESO PR Photo 16a/02 [Preview - JPEG: 756 x 400 pix - 363k] [Normal - JPEG: 1511 x 800 pix - 1.2M] ESO PR Photo 16b/02 ESO PR Photo 16b/02 [Preview - JPEG: 461 x 400 pix - 196k] [Normal - JPEG: 921 x 800 pix - 606k] Caption : PR Photo 16a/02 : "First Light" test observation with the GIRAFFE spectrograph of about 50 high-quality spectra (10 min exposure at spectral resolution 7,000) of stars in the Milky Way disk, in the early morning of July 3, 2002. The stars have magnitudes of 12 - 16 and are all of solar type. The photo shows part of the image recorded with a 2000 x 4000 pixel CCD detector at the focal plane of the spectrograph. Each stellar spectrum is seen as one vertical line - some of the absorption lines can be seen as dark horizontal features. PR Photo 16b/02 shows a small part of this image. The three strong absorption lines that are visible as horizontal, dark lines in the lower part of the
Blurred Star Image Processing for Star Sensors under Dynamic Conditions
Zhang, Weina; Quan, Wei; Guo, Lei
The precision of star point location is significant to identify the star map and to acquire the aircraft attitude for star sensors. Under dynamic conditions, star images are not only corrupted by various noises, but also blurred due to the angular rate of the star sensor. According to different angular rates under dynamic conditions, a novel method is proposed in this article, which includes a denoising method based on adaptive wavelet threshold and a restoration method based on the large angular rate. The adaptive threshold is adopted for denoising the star image when the angular rate is in the dynamic range. Then, the mathematical model of motion blur is deduced so as to restore the blurred star map due to large angular rate. Simulation results validate the effectiveness of the proposed method, which is suitable for blurred star image processing and practical for attitude determination of satellites under dynamic conditions. PMID:22778666
HAZMAT. III. The UV Evolution of Mid- to Late-M Stars with GALEX
Schneider, Adam C.; Shkolnik, Evgenya L.
Low-mass stars are currently the most promising targets for detecting and characterizing habitable planets in the solar neighborhood. However, the ultraviolet (UV) radiation emitted by such stars can erode and modify planetary atmospheres over time, drastically affecting their habitability. Thus, knowledge of the UV evolution of low-mass stars is critical for interpreting the evolutionary history of any orbiting planets. Shkolnik & Barman used photometry from the Galaxy Evolution Explorer (GALEX) to show how UV emission evolves for early-type M stars (>0.35 M ⊙). In this paper, we extend their work to include both a larger sample of low-mass stars with known ages as well as M stars with lower masses. We find clear evidence that mid- and late-type M stars (0.08–0.35 M ⊙) do not follow the same UV evolutionary trend as early-Ms. Lower-mass M stars retain high levels of UV activity up to field ages, with only a factor of 4 decrease on average in GALEX NUV and FUV flux density between young (<50 Myr) and old (∼5 Gyr) stars, compared to a factor of 11 and 31 for early-Ms in NUV and FUV, respectively. We also find that the FUV/NUV flux density ratio, which can affect the photochemistry of important planetary biosignatures, is mass- and age-dependent for early-Ms, but remains relatively constant for the mid- and late-type Ms in our sample.
GRACE star camera noise
Harvey, Nate
Extending results from previous work by Bandikova et al. (2012) and Inacio et al. (2015), this paper analyzes Gravity Recovery and Climate Experiment (GRACE) star camera attitude measurement noise by processing inter-camera quaternions from 2003 to 2015. We describe a correction to star camera data, which will eliminate a several-arcsec twice-per-rev error with daily modulation, currently visible in the auto-covariance function of the inter-camera quaternion, from future GRACE Level-1B product releases. We also present evidence supporting the argument that thermal conditions/settings affect long-term inter-camera attitude biases by at least tens-of-arcsecs, and that several-to-tens-of-arcsecs per-rev star camera errors depend largely on field-of-view.
Collapse of axion stars
Eby, Joshua; Leembruggen, Madelyn; Suranyi, Peter; ...
Axion stars, gravitationally bound states of low-energy axion particles, have a maximum mass allowed by gravitational stability. Weakly bound states obtaining this maximum mass have sufficiently large radii such that they are dilute, and as a result, they are well described by a leading-order expansion of the axion potential. Here, heavier states are susceptible to gravitational collapse. Inclusion of higher-order interactions, present in the full potential, can give qualitatively different results in the analysis of collapsing heavy states, as compared to the leading-order expansion. In this work, we find that collapsing axion stars are stabilized by repulsive interactions present inmore » the full potential, providing evidence that such objects do not form black holes. In the last moments of collapse, the binding energy of the axion star grows rapidly, and we provide evidence that a large amount of its energy is lost through rapid emission of relativistic axions.« less
Dynamical boson stars.
Liebling, Steven L; Palenzuela, Carlos
The idea of stable, localized bundles of energy has strong appeal as a model for particles. In the 1950s, John Wheeler envisioned such bundles as smooth configurations of electromagnetic energy that he called geons , but none were found. Instead, particle-like solutions were found in the late 1960s with the addition of a scalar field, and these were given the name boson stars . Since then, boson stars find use in a wide variety of models as sources of dark matter, as black hole mimickers, in simple models of binary systems, and as a tool in finding black holes in higher dimensions with only a single Killing vector. We discuss important varieties of boson stars, their dynamic properties, and some of their uses, concentrating on recent efforts.
Giant star seismology
Hekker, S.; Christensen-Dalsgaard, J.
The internal properties of stars in the red-giant phase undergo significant changes on relatively short timescales. Long near-uninterrupted high-precision photometric timeseries observations from dedicated space missions such as CoRoT and Kepler have provided seismic inferences of the global and internal properties of a large number of evolved stars, including red giants. These inferences are confronted with predictions from theoretical models to improve our understanding of stellar structure and evolution. Our knowledge and understanding of red giants have indeed increased tremendously using these seismic inferences, and we anticipate that more information is still hidden in the data. Unraveling this will further improve our understanding of stellar evolution. This will also have significant impact on our knowledge of the Milky Way Galaxy as well as on exo-planet host stars. The latter is important for our understanding of the formation and structure of planetary systems.
Pulsating Star Mystery Solved
By discovering the first double star where a pulsating Cepheid variable and another star pass in front of one another, an international team of astronomers has solved a decades-old mystery. The rare alignment of the orbits of the two stars in the double star system has allowed a measurement of the Cepheid mass with unprecedented accuracy. Up to now astronomers had two incompatible theoretical predictions of Cepheid masses. The new result shows that the prediction from stellar pulsation theory is spot on, while the prediction from stellar evolution theory is at odds with the new observations. The new results, from a team led by Grzegorz Pietrzyński (Universidad de Concepción, Chile, Obserwatorium Astronomiczne Uniwersytetu Warszawskiego, Poland), appear in the 25 November 2010 edition of the journal Nature. Grzegorz Pietrzyński introduces this remarkable result: "By using the HARPS instrument on the 3.6-metre telescope at ESO's La Silla Observatory in Chile, along with other telescopes, we have measured the mass of a Cepheid with an accuracy far greater than any earlier estimates. This new result allows us to immediately see which of the two competing theories predicting the masses of Cepheids is correct." Classical Cepheid Variables, usually called just Cepheids, are unstable stars that are larger and much brighter than the Sun [1]. They expand and contract in a regular way, taking anything from a few days to months to complete the cycle. The time taken to brighten and grow fainter again is longer for stars that are more luminous and shorter for the dimmer ones. This remarkably precise relationship makes the study of Cepheids one of the most effective ways to measure the distances to nearby galaxies and from there to map out the scale of the whole Universe [2]. Unfortunately, despite their importance, Cepheids are not fully understood. Predictions of their masses derived from the theory of pulsating stars are 20-30% less than predictions from the theory of the
Chemical Evolution of Binary Stars
Izzard, R. G.
Energy generation by nuclear fusion is the fundamental process that prevents stars from collapsing under their own gravity. Fusion in the core of a star converts hydrogen to heavier elements from helium to uranium. The signature of this nucleosynthesis is often visible in a single star only for a very short time, for example while the star is a red giant or, in massive stars, when it explodes. Contrarily, in a binary system nuclear-processed matter can captured by a secondary star which remains chemically polluted long after its more massive companion star has evolved and died. By probing old, low-mass stars we gain vital insight into the complex nucleosynthesis that occurred when our Galaxy was much younger than it is today. Stellar evolution itself is also affected by the presence of a companion star. Thermonuclear novae and type Ia supernovae result from mass transfer in binary stars, but big questions still surround the nature of their progenitors. Stars may even merge and one of the challenges for the future of stellar astrophysics is to quantitatively understand what happens in such extreme systems. Binary stars offer unique insights into stellar, galactic and extragalactic astrophysics through their plethora of exciting phenomena. Understanding the chemical evolution of binary stars is thus of high priority in modern astrophysics.
Spectral Analysis of the O(He)-Type Central Stars of the Planetary Nebulae K 1-27 and LoTr 4
Reindl, N.; Ringat, E.; Rauch, T.; Werner, K.; Kruk, J. W.
The four known O(He) stars are the only amongst the hottest post-AGB stars whose atmospheres are composed of almost pure helium. Thus, their evolution deviates from the hydrogen-defiCient post-AGB evolutionary sequence of carbon-dominated stars like e.g. PG 1159 stars. The origin of the O(He) stars is still not explained. They might be either post-early AGB stars or the progeny of R Coronae Borealis stars. We present preliminary results of a non-LTE spectral analysis based on FUSE and HST/COS observations.
Main-Sequence O Stars in NGC 6231: Enhanced Winds
Morrison, Nancy D.
Three late O-type main-sequence stars in the open cluster NGC 6231 will be observed with IUE at high dispersion, and their C IV and N V resonance-line profiles will be studied. From low-dispersion IUE observations, 10 members of the cluster have been found to have anomalously strong C IV resonance lines for their spectral types. Massa, Savage, and Cassinelli (1984) observed two of these "UV peculiar" stars (spectral types B0.5 V and B1 V) at high dispersion. They found that the C IV lines have a strong, broad, shortward-shifted absorption component, which suggests a greatly enhanced wind relative to the average for the spectral type. They proposed that the enhancement is due to an overabundance of C. Recently, however, Grigsby, Gordon, Morrison, and Zimba (1992) showed from optical spectra that these stars have normal C abundances. Thus, there is not yet a convincing explanation for these strikingly anomalous stellar winds. By extending the temperature range over which the phenomenon has been studied at high dispersion, however, we expect to gain new physical information. From wind modeling of the line profiles, we will derive mass-loss rates and terminal velocities, and we will test whether these winds are described by radiation-driven wind theory.
Synthetic guide star generation
Payne, Stephen A [Castro Valley, CA; Page, Ralph H [Castro Valley, CA; Ebbers, Christopher A [Livermore, CA; Beach, Raymond J [Livermore, CA
A system for assisting in observing a celestial object and providing synthetic guide star generation. A lasing system provides radiation at a frequency at or near 938 nm and radiation at a frequency at or near 1583 nm. The lasing system includes a fiber laser operating between 880 nm and 960 nm and a fiber laser operating between 1524 nm and 1650 nm. A frequency-conversion system mixes the radiation and generates light at a frequency at or near 589 nm. A system directs the light at a frequency at or near 589 nm toward the celestial object and provides synthetic guide star generation.
A Star on Earth
Prager, Stewart; Zwicker, Andrew; Hammet, Greg; Tresemer, Kelsey; Diallo, Ahmed
At the Energy Department's Princeton Plasma Physics Lab, scientists are trying to accomplish what was once considered the realm of science fiction: create a star on Earth. The National Spherical Torus Experiment (NSTX) is a magnetic fusion device that is used to study the physics principles of spherically shaped plasmas -- hot ionized gases in which, under the right conditions, nuclear fusion will occur. Fusion is the energy source of the sun and all of the stars. Not just limited to theoretical work, the NSTX is enabling cutting-edge research to develop fusion as a future energy source.
Payne, Stephen A.; Page, Ralph H.; Ebbers, Christopher A.; Beach, Raymond J.
NuSTAR Briefing
Yunjin Kim, NuSTAR project manager at the Jet Propulsion Laborartory (JPL), talks about NASA's Spectroscopic Telescope Array (NuStar) during a briefing, Wednesday, May 30, 2012, at NASA Headquarters in Washington. Imaging light in the high-energy, short-wavelength X-ray range, the telescope will aim to study how black holes form and evolve along with galaxies. The instrument, packed aboard an Orbital Sciences Pegasus XL rocket is set to launch from a plane in midair no earlier than June 13 from Kwajalein Atoll in the Marshall Islands. Photo Credit: (NASA/Paul E. Alers)
VPP Star recognition
Stennis Space Center Deputy Director Rick Gilbrech (right) accepts a plaque designating the test facility as a Voluntary Protection Program Star site. Presenting the plaque is Clyde Payne, area director for the Occupational Safety and Health Administration in Jackson, Miss. OSHA established VPP in 1982 as a proactive safety management model to recognize excellence in safety and health. Since then, more than 2,000 organizations have been designated VPP Star sites. To reach that goal, an organization must demonstrate comprehensive and successful safety and health management programs in the workplace.
A Real Shooting Star
[figure removed for brevity, see original site] Click on the image for movie of A Real Shooting Star
This artist's animation illustrates a star flying through our galaxy at supersonic speeds, leaving a 13-light-year-long trail of glowing material in its wake. The star, named Mira (pronounced my-rah) after the latin word for 'wonderful,' sheds material that will be recycled into new stars, planets and possibly even life. NASA's Galaxy Evolution Explorer discovered the long trail of material behind Mira during its survey of the entire sky in ultraviolet light.
The animation begins by showing a close-up of Mira -- a red-giant star near the end of its life. Red giants are red in color and extremely bloated; for example, if a red giant were to replace our sun, it would engulf everything out to the orbit of Mars. They constantly blow off gas and dust in the form of stellar winds, supplying the galaxy with molecules, such as oxygen and carbon, that will make their way into new solar systems. Our sun will mature into a red giant in about 5 billion years.
As the animation pulls out, we can see the enormous trail of material deposited behind Mira as it hurls along between the stars. Like a boat traveling through water, a bow shock, or build up of gas, forms ahead of the star in the direction of its motion. Gas in the bow shock is heated and then mixes with the cool hydrogen gas in the wind that is blowing off Mira. This heated hydrogen gas then flows around behind the star, forming a turbulent wake.
Why does the trailing hydrogen gas glow in ultraviolet light? When it is heated, it transitions into a higher-energy state, which then loses energy by emitting ultraviolet light - a process known as fluorescence.
Finally, the artist's rendering gives way to the actual ultraviolet image taken by the Galaxy Evolution Explorer
Mira is located 350 light-years from Earth in the constellation Cetus, otherwise known as the whale. Coincidentally, Mira
The Carbon Stars Adventure
Rau, Gioia; Paladini, C.; Hron, J.; Aringer, B.; Eriksson, K.; Groenewegen, M. A. T.; Nowotny, W.
We compare in a systematic way spectrometric, photometric and mid-infrared (VLTI/MIDI) interferometric measurements with different types of model atmospheres. Self-consistent dynamic model atmospheres in particular were used to interpret in a consistent way the dynamic behavior of gas and dust. The results underline how the joint use of different kind of observations, as photometry, spectroscopy and interferometry, is essential to understand the atmospheres of pulsating C-rich AGB stars. The sample of C-rich stars discussed in this work provides crucial constraints for the atmospheric structure.
The Drifting Star
By studying in great detail the 'ringing' of a planet-harbouring star, a team of astronomers using ESO's 3.6-m telescope have shown that it must have drifted away from the metal-rich Hyades cluster. This discovery has implications for theories of star and planet formation, and for the dynamics of our Milky Way. ESO PR Photo 09a/08 ESO PR Photo 09a/08 Iota Horologii The yellow-orange star Iota Horologii, located 56 light-years away towards the southern Horologium ("The Clock") constellation, belongs to the so-called "Hyades stream", a large number of stars that move in the same direction. Previously, astronomers using an ESO telescope had shown that the star harbours a planet, more than 2 times as large as Jupiter and orbiting in 320 days (ESO 12/99). But until now, all studies were unable to pinpoint the exact characteristics of the star, and hence to understand its origin. A team of astronomers, led by Sylvie Vauclair from the University of Toulouse, France, therefore decided to use the technique of 'asteroseismology' to unlock the star's secrets. "In the same way as geologists monitor how seismic waves generated by earthquakes propagate through the Earth and learn about the inner structure of our planet, it is possible to study sound waves running through a star, which forms a sort of large, spherical bell," says Vauclair. The 'ringing' from this giant musical instrument provides astronomers with plenty of information about the physical conditions in the star's interior. And to 'listen to the music', the astronomers used one of the best instruments available. The observations were conducted in November 2006 during 8 consecutive nights with the state-of-the-art HARPS spectrograph mounted on the ESO 3.6-m telescope at La Silla. Up to 25 'notes' could be identified in the unique dataset, most of them corresponding to waves having a period of about 6.5 minutes. These observations allowed the astronomers to obtain a very precise portrait of Iota Horologii: its
ABOUT EXOBIOLOGY: THE CASE FOR DWARF K STARS
Cuntz, M.; Guinan, E. F., E-mail: cuntz@uta.edu, E-mail: edward.guinan@villanova.edu
One of the most fundamental topics of exobiology concerns the identification of stars with environments consistent with life. Although it is believed that most types of main-sequence stars might be able to support life, particularly extremophiles, special requirements appear to be necessary for the development and sustainability of advanced life forms. From our study, orange main-sequence stars, ranging from spectral type late-G to mid-K (with a maximum at early K), are most promising. Our analysis considers a variety of aspects, including (1) the frequency of the various types of stars, (2) the speed of stellar evolution in their lifetimes, (3)more » the size of the stellar climatological habitable zones (CLI-HZs), (4) the strengths and persistence of their magnetic-dynamo-generated X-ray–UV emissions, and (5) the frequency and severity of flares, including superflares; both (4) and (5) greatly reduce the suitability of red dwarfs to host life-bearing planets. The various phenomena show pronounced dependencies on the stellar key parameters such as effective temperature and mass, permitting the assessment of the astrobiological significance of various types of stars. Thus, we developed a "Habitable-Planetary-Real-Estate Parameter� (HabPREP) that provides a measure for stars that are most suitable for planets with life. Early K stars are found to have the highest HabPREP values, indicating that they may be "Goldilocks� stars for life-hosting planets. Red dwarfs are numerous, with long lifetimes, but their narrow CLI-HZs and hazards from magnetic activity make them less suitable for hosting exolife. Moreover, we provide X-ray–far-UV irradiances for G0 V–M5 V stars over a wide range of ages.« less
Cuntz, M.; Guinan, E. F.
One of the most fundamental topics of exobiology concerns the identification of stars with environments consistent with life. Although it is believed that most types of main-sequence stars might be able to support life, particularly extremophiles, special requirements appear to be necessary for the development and sustainability of advanced life forms. From our study, orange main-sequence stars, ranging from spectral type late-G to mid-K (with a maximum at early K), are most promising. Our analysis considers a variety of aspects, including (1) the frequency of the various types of stars, (2) the speed of stellar evolution in their lifetimes, (3) the size of the stellar climatological habitable zones (CLI-HZs), (4) the strengths and persistence of their magnetic-dynamo-generated X-ray-UV emissions, and (5) the frequency and severity of flares, including superflares; both (4) and (5) greatly reduce the suitability of red dwarfs to host life-bearing planets. The various phenomena show pronounced dependencies on the stellar key parameters such as effective temperature and mass, permitting the assessment of the astrobiological significance of various types of stars. Thus, we developed a "Habitable-Planetary-Real-Estate Parameter� (HabPREP) that provides a measure for stars that are most suitable for planets with life. Early K stars are found to have the highest HabPREP values, indicating that they may be "Goldilocks� stars for life-hosting planets. Red dwarfs are numerous, with long lifetimes, but their narrow CLI-HZs and hazards from magnetic activity make them less suitable for hosting exolife. Moreover, we provide X-ray-far-UV irradiances for G0 V-M5 V stars over a wide range of ages.
Hidden Milky Way star clusters hosting Wolf-Rayet stars
Kurtev, R.; Borissova, J.; Ivanov, V. D.; Georgiev, L.
A noticeable fraction of the hidden young star clusters contain WR and O stars providing us with unique laboratories to study the evolution of these rare objects and their maternity places. We are reporting the reddening, the distance and age of two new members of the family of massive young Galactic clusters, hosting WR stars - Glimpse 23 and Glimpse 30.
Dead Star Warps Light of Red Star Artist Animation
This artist concept depicts an ultra-dense dead star, called a white dwarf, passing in front of a small red star. NASA planet-hunting Kepler was able to detect gravitational lensing by measuring a strangely subtle dip in the star brightness.
Stellar parameters of Be stars observed with X-shooter
Shokry, A.; Rivinius, Th.; Mehner, A.; Martayan, C.; Hummel, W.; Townsend, R. H. D.; Mérand, A.; Mota, B.; Faes, D. M.; Hamdy, M. A.; Beheary, M. M.; Gadallah, K. A. K.; Abo-Elazm, M. S.
Aims: The X-shooter archive of several thousand telluric standard star spectra was skimmed for Be and Be shell stars to derive the stellar fundamental parameters and statistical properties, in particular for the less investigated late-type Be stars and the extension of the Be phenomenon into early A stars. Methods: An adapted version of the BCD method is used, using the Balmer discontinuity parameters to determine effective temperature and surface gravity. This method is optimally suited for late B stars. The projected rotational velocity was obtained by profile fitting to the Mg ii lines of the targets, and the spectra were inspected visually for the presence of peculiar features such as the infrared Ca ii triplet or the presence of a double Balmer discontinuity. The Balmer line equivalent widths were measured, but they are only useful for determining the pure emission contribution in a subsample of Be stars owing to uncertainties in determining the photospheric contribution. Results: A total of 78, mostly late-type, Be stars, were identified in the X-shooter telluric standard star archive, out of which 48 had not been reported before. We confirm the general trend that late-type Be stars have more tenuous disks and are less variable than early-type Be stars. The relatively large number (48) of relatively bright (V> 8.5) additional Be stars casts some doubt on the statistics of late-type Be stars; they are more common than currently thought. The Be/B star fraction may not strongly depend on spectral subtype. Based on observations made with ESO Telescopes at the La Silla Paranal Observatory under program IDs 60.A-9022, 60.A-9024, 077.D-0085, 085.A-0962, 185.D-0056, 091.B-0900, and 093.D-0415.Table 6 is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/609/A108
HR 8844: A New Transition Object between the Am Stars and the HgMn Stars?
Monier, R.; Gebran, M.; Royer, F.; Kilicoglu, T.; Frémat, Y.
While monitoring a sample of apparently slowly rotating superficially normal early-A stars, we have discovered that HR 8844 (A0 V) is actually a new chemically peculiar star. We first compared the high-resolution spectrum of HR 8844 with that of four slow rotators near A0V (ν Cap, ν Cnc, Sirius A, and HD 72660) to highlight similarities and differences. The lines of Ti II, Cr II, Sr II, and Ba II are conspicuous features in the high-resolution high signal-to-noise SOPHIE spectra of HR 8844 and much stronger than in the spectra of the normal star ν Cap. The Hg II line at 3983.93 Å is also present in a 3.5% blend. Selected unblended lines of 31 chemical elements from He up to Hg have been synthesized using model atmospheres computed with ATLAS9 and the spectrum synthesis code SYNSPEC48 including hyperfine structure of various isotopes when relevant. These synthetic spectra have been adjusted to the mean SOPHIE spectrum of HR 8844, and high-resolution spectra of the comparison stars. Chi-squares were minimized to derive abundances or upper limits to the abundances of these elements for HR 8844 and the comparison stars. HR 8844 is found to have underabundances of He, C, O, Mg, Ca, and Sc, mild enhancements of Ti, V, Cr, Mn, and distinct enhancements of the heavy elements Sr, Y, Zr, Ba, La, Pr, Sm, Eu, and Hg, the overabundances increasing steadily with atomic number. This chemical pattern suggests that HR 8844 may actually be a new transition object between the coolest HgMn stars and the Am stars.
Companions and Environments of Low-Mass Stars: From Star-Forming Regions to the Field
Ward-Duong, Kimberly; Patience, Jenny; De Rosa, Robert J.; Bulger, Joanna; Rajan, Abhijith; Goodwin, Simon; Parker, Richard J.; McCarthy, Donald W.; Kulesa, Craig; van der Plas, Gerrit; Menard, Francois; Pinte, Christophe; Jackson, Alan Patrick; Bryden, Geoffrey; Turner, Neal J.; Harvey, Paul M.; Hales, Antonio
We present results from two studies probing the multiplicity and environmental properties of low-mass stars: (1) The MinMs (M-dwarfs in Multiples) Survey, a large, volume-limited survey of 245 field M-dwarfs within 15 pc, and (2) the TBOSS (Taurus Boundary of Stellar/Substellar) Survey, an ongoing study of disk properties for the lowest-mass members within the Taurus star-forming region. The MinMs Survey provides new measurements of the companion star fraction, separation distribution, and mass ratio distribution for the nearest K7-M6 dwarfs, utilizing a combination of high-resolution adaptive optics imaging and digitized widefield archival plates to cover an unprecedented separation range of ~1-10,000 AU. Within these data, we also identify companions below the stellar/brown dwarf boundary, enabling characterization of the substellar companion population to low-mass field stars. For the much younger population in Taurus, we present results from ALMA Band 7 continuum observations of low-mass stellar and substellar Class II objects, spanning spectral types from M4-M7.75. The sub-millimeter detections of these disks provide key estimates of the dust mass in small grains, which is then assessed within the context of region age, environment, and viability for planet formation. This young population also includes a number of interesting young binary systems. Covering both young (1-2 Myr) and old (>5 Gyr) populations of low-mass stars, the results from these studies provide benchmark measurements on the population statistics of low-mass field stars, and on the early protoplanetary environments of their younger M-star counterparts.
Hubble Sweeps a Messy Star Factory
This sprinkle of cosmic glitter is a blue compact dwarf galaxy known as Markarian 209. Galaxies of this type are blue-hued, compact in size, gas-rich, and low in heavy elements. They are often used by astronomers to study star formation, as their conditions are similar to those thought to exist in the early Universe. Markarian 209 in particular has been studied extensively. It is filled with diffuse gas and peppered with star-forming regions towards its core. This image captures it undergoing a particularly dramatic burst of star formation, visible as the lighter blue cloudy region towards the top right of the galaxy. This clump is filled with very young and hot newborn stars. This galaxy was initially thought to be a young galaxy undergoing its very first episode of star formation, but later research showed that Markarian 209 is actually very old, with an almost continuous history of forming new stars. It is thought to have never had a dormant period — a period during which no stars were formed — lasting longer than 100 million years. The dominant population of stars in Markarian 209 is still quite young, in stellar terms, with ages of under 3 million years. For comparison, the sun is some 4.6 billion years old, and is roughly halfway through its expected lifespan. The observations used to make this image were taken using Hubble's Wide Field Camera 3 and Advanced Camera for Surveys, and span the ultraviolet, visible, and infrared parts of the spectrum. A scattering of other bright galaxies can be seen across the frame, including the bright golden oval that could, due to a trick of perspective, be mistaken as part of Markarian 209 but is in fact a background galaxy. Credit: ESA/Hubble & NASA Acknowledgement: Nick Rose NASA image use policy. NASA Goddard Space Flight Center enables NASA's mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA's accomplishments