Cycle 2 (2010) Accepted Guest Observer Programs
PHOTOMETRY OF AN ECLIPSING SYSTEM WITH A WHITE DWARF COMPONENT, THE ONLY ONE KNOWN IN THE KEPLER FOV
Roi Alonso
Observatoire Astronomique de l'Universite de Geneve
GO20043
+data
We plan to continue our research on the only system of a white dwarf with a M star eclipsing component that is accesible to Kepler FOV. Extending the observations through Cycle2 will allow us to 1) improve the precision on the orbital parameters, 2) study the anual evolution of the flare activity on the M companion and its dependance with the orbital phase, 3) study the evolution of magnetic active regions on any of the components, 4) improve the precision on the expected detection of a secondary eclipse, 5) gain valuable data on the O-C residuals of the 1040 eclipses/year that Kepler is able to obtain, that might allow the detection of small stellar companions and probably substellar, and 6) search for pulsations of the WD component.
SIMULTANEOUS OPTICAL AND RADIO MONITORING OF NEARBY GALAXY NUCLEI WITH KEPLER AND THE ALLEN TELESCOPE ARRAY
Geoffrey Bower
We propose to obtain simultaneous optical and radio light curves for the nuclear regions of a sample of 117 nearby galaxies, including some which are known to host AGN. These light curves will be valuable for constraining physical conditions in the galaxies studied, including the origin of AGN activity and of radio-loudness, black hole accretion mechanisms, and the presence of supernovae, X-ray binaries, or other variables in the nuclear regions of galaxies. Optical and radio data will probe a range of energies and size scales. The Allen Telescope Array (ATA) is a radio telescope designed for fast surveying of large areas of sky, with a particular emphasis on transient and variable sources. With a 5 square degree field of view at 20 cm, a sensitivity of ~10 mJy in a one minute observation, and the ability to observe simultaneously in two 100 MHz bands anywhere in the 0.5 - 10 GHz range, the ATA is opening new regions of parameter space in cadence, sensitivity, and area covered. Several ongoing surveys are in progress, including a survey of a ~10 square degree field in Cygnus which is observed for ~8 hours every few days. This survey is designed to study transient emission from objects such as supernovae and gamma ray bursts, as well as variable sources such as AGN and flare stars. Since we have coverage of the full 10 square degree ATA field, and not just the objects we propose to observe with Kepler, we will also be able to supply radio light curves to the Kepler team for any other objects (e.g., brown dwarfs, flare stars, etc.) in our radio data which show interesting characteristics such as variability. We select a sample of galaxies (including known AGN), most of which are associated with the low-redshift rich galaxy cluster Abell 2319, within the Kepler and ATA Cygnus Survey fields of view. The ATA will observe this field with a rolling cadence, allowing us to explore variability on many timescales, from minutes to years. Tools have been developed for imaging, catalog extraction, and light curve generation which will allow us to easily compare variability in the radio with variability at optical wavelengths from Kepler.
STARSPOT EVOLUTION ON ACTIVE LATE-TYPE STARS IN THE KEPLER FIELD - CYCLE 2
University Of Colorado, Boulder
Starspots on late-type stars are a direct manifestation of the photospheric emergence of strong dynamo-generated magnetic fields. We propose to extend our Cycle 1 project of 30 minute cadence Kepler photometry, in which we are investigating how activity phenomena such as the growth, migration, and decay of starspots, differential rotation, activity cycles,and flaring operate on single and binary stars with a wide range of mass (and hence convection zone depth), with the expectation that such investigations will stimulate and enable theoretical studies of magnetic flux generation and transport processes in the extreme regime of fast rotation that any successful theory must be able to address. Our sample of 186 active stars was selected based on GALEX FUV and NUV imaging of the Kepler field. For accurately measuring the longitudes of active regions, spot filling-factor maps will be obtained from the Kepler photometry using light-curve inversion methods. Time-series analysis, using both Fourier and wavelet techniques, are used to obtain accurate rotation periods. After which the phased light-curves are processed with our existing inversion codes using both the Occamian approach and the Maximum Entropy method. A full suite of supporting high resolution optical spectroscopic observations will be obtained using the Hobby-Eberly, Keck, and Apache Point Observatory telescopes to accurately determine the stellar parameters, including effective temperature, surface gravity, and projected rotational velocity, and to identify which stars are spectroscopic or eclipsing binaries and measure their radial velocity curves. For many targets Doppler imaging, both conventional and magnetic, will be pursued.
A SEARCH FOR ASTEROIDS ORBITING WHITE DWARFS
Rosanne Di Stefano
Smithsonian Institution/Smithsonian Astrophysical Observatory
Do white dwarfs host asteroid systems? Because asteroids are fossils of planet formation, the answer to this question has implications for our understanding of the earliest stages of planetary systems. In addition, because white dwarfs are remnants of stars like our Sun, the discovery of asteroids orbiting them may teach us about the evolution and survival of planetary systems. NASA's launch of Kepler provides us with the first tool capable of helping to answer this question. We propose that Kepler observe two of the brightest white dwarfs in its field in 1-minute cadence mode with the goal of searching for transits by asteroids in orbit around them. This scientific investigation makes full use of NASA's newest mission, and in fact would not be possible without it. To detect the passage of 100-km class objects against the disk of a white dwarf requires Kepler's unique photometric sensitivity and continuous monitoring. The analysis we propose to conduct will open a new field of endeavor that can help achieve NASA's science goals for the study of the origin and evolution of planetary systems.
LENSING IN THE KEPLER FIELD
Lensing events occur regularly in the Kepler field. The Kepler mission therefore provides a unique and scientifically important opportunity to monitor lensing light curves. The unprecedented photometric sensitivity combined with 30-minute cadence over a period of months can be utilized to accomplish important goals These include (1) high-precision verification of the form of the lensing light curve predicted by general relativity, and (2) high-precision tests for a variety of system parameters, including lens mass and multiplicity, source multiplicity, parallax, and source size. Detectable lensing is most likely to be caused by nearby high-proper-motion masses,i.e., mesolenses. The Einstein rings of nearby masses are large enough that astrometric effects, as well as photometric variations may be detectable. A large set of high-proper-motion stars is already likely to be observed by Kepler during the coming year. We propose to analyze Kepler data from all of these. In addition, we propose that a new set of high-proper-motion stars be observed during cycle 2. The newly selected stars are those with the highest probability of producing an event. In order to conduct the analysis we propose, we will develop tools that allow the community of scientists who will use Kepler data to check for evidence of lensing events in the entire data set.
HIGH METALLICITY IN CATACLYSMIC VARIABLES AND THE RISE OF SUPERNOVAE
Peter Garnavich
We propose to study two of the three known cataclysmic variables (CV) in the old, metal-rich open cluster NGC 6791. Both appear to be dwarf novae, although, ground observations have been sparse. The instability of the accretion disk producing the dwarf nova outbursts may depend on the metal abundance of the accreting gas. Photometric properties, such as cycle time and outburst amplitude, maybe enhanced in the unique NGC 6791 environment. We also propose to monitor 93 bright galaxies at z<0.05 in the Kepler field to obtain the early light curve of a supernova. SDSS-II studies of type Ia light curves show that the rise-times are shorter than previously thought and the shape of the early rise provides insight into the explosion mechanism.
AN EXTENDED SEARCH FOR CIRCUMBINARY COMPANIONS OF INTERMEDIATE-MASS ECLIPSING BINARY STARS
Douglas Gies
There is abundant evidence that stellar companions are more commonplace among the more massive stars, and it is possible that massive star formation processes lead directly to binary and multiple systems as a repository of the angular momentum of the natal cloud. In particular, the formation of a close binary may require the presence of a distant third star to carry the bulk of the angular momentum. Our goal in this proposal is to search for evidence of companions surrounding close eclipsing pairs of intermediate mass, B, A, and F-type stars. Since these close binaries have periods of a few days, the search will focus on dynamically stable outer companions with orbital periods in the range 0.3 to 26 months. We will use precise light curves from Kepler of 40 binaries to measure accurate eclipse timings, and we will search for companions by investigating periodic variations in the times of minima caused by the light travel time across the orbital displacement of the close binary. In favorable situations, we will be able to detect the presence of objects as small as brown dwarf stars and/or massive planets. This work will establish the occurrence of low mass companions among intermediate mass stars. We began this program in Cycle 1 and here we seek an extension through Cycle 2 to double the size of the sample and to search for longer period companions.
TRANSITION IN VARIABLE STARS: FROM SOLAR-TYPE TO GAMMA DORADUS-TYPE
Joyce Guzik
Los Alamos National Laboratory/University of California
The Main Sequence solar-type pulsators are characterized by acoustic oscillation modes excited by turbulent granular convection in the upper convective boundary layer. As the stellar mass increases the convection zone shrinks, the scale and intensity of the turbulent motions increases, providing more energy for excitation of acoustic modes. When the stellar mass reaches about 1.6 solar masses (the gamma Doradus class) the upper convection zone consists of two very thin layers corresponding to H and He ionization, and in addition to the acoustic (p) modes the stars show strong internal gravity (g) modes The thin convection zone is often considered insignificant for the stellar dynamics and variability. However, recent 3D radiative hydrodynamics simulations reveal supersonic granular-type convection of the scale significantly larger than the solar granulation, and strong overshooting plumes penetrating into the stable radiative zone. These plumes may contribute to the excitation of the g-modes or hybrid modes with p- and g-characteristics. Pulsations of these types despite substantial efforts have not been observed on Sun. The goal of this proposal is investigate the physics of the interaction between the turbulent convection and oscillations along the Main Sequence, from the solar-type stars to more massive gamma Doradus stars. This interaction will be investigated by comparing the convective and oscillation spectra with the numerical simulation models. The numerical simulations, specifically developed at NASA Ames and Stanford Center for Turbulence Research, will provide a critical theoretical support for interpretation of the observed variability of these stars. This type of turbulent convection cannot be correctly described by the traditional mixing-length models. The proposed investigation will include a series of interesting questions about the role of turbulent surface and subsurface motions in the stellar variability and magnetism, e.g. how the supergranulation pattern changes in this transition, what is the effect of this transition on the local dynamo, formation of magnetic structures and atmospheric heating. The gamma Doradus stars show an increase in UV radiation but the mechanism of this is unclear. The Kepler short-cadence data and the realistic numerical simulations carried out in conjunction with project offer a unique opportunity to investigate the physics of the transition in turbulent convection and oscillations, and also potential role of magnetic fields. This will provide an important insight for the understanding of these and other types of variable stars.
A SEARCH FOR HYBRID GAMMA DORADUS/DELTA SCUTI PULSATING VARIABLES--IMPROVING THE STATISTICS
The delta Scuti and gamma Doradus pulsating variables are main-sequence (core hydrogen-burning) stars with masses somewhat larger than the sun (1.2 to 2.5 solar masses). The lower-mass gamma Dor stars are pulsating in nonradial gravity modes with periods of near one day, whereas the delta Scuti stars are radial and nonradial p-mode (acoustic mode) pulsators with periods of order two hours. Because of the near one-day periods of gamma Dor stars, it is very difficult to discover these stars and determine their pulsation frequency spectrum from ground-based photometry due to the 1 cycle/day alias, whereas Kepler observations have been able to detect them easily with one or two quarters of monitoring. Hybrid gamma Dor/delta Sct stars are among the most interesting targets for asteroseismology because the two types of modes (pressure and gravity) probe different regions of the star and are sensitive to the details of the two different driving mechanisms. Because the pulsations are driven by two different, and somewhat mutually exclusive, mechanisms, hybrid stars exhibiting both types of pulsations are expected to exist only in a small overlapping region of temperature-luminosity space in the Hertzsprung-Russell diagram. Before the advent of the Kepler and CoRoT missions, only four hybrid gamma Dor/delta Scuti pulsators had been discovered. Now the first analysis by the Kepler Asteroseismic Consortium (KASC) of 234 targets showing pulsations of either type has revealed hybrid behavior in essentially all of them! (Grighacene et al., ApJL in press, astro-ph 1001.0747) The existence and properties of these hybrids raise a number of questions: Why are hybrids much more common than predicted by theory? Why do some hybrid stars show frequencies in the gap predicted by theory between the gamma Dor and delta Sct frequency range? Are unknown pulsation mechanisms at work ? We hope to answer these questions by improving the statistics on the occurrence and properties of hybrids among the gamma Dor and delta Sct stars using Kepler observations. We propose to supplement the KASC search by observing an additional 187 stars from the Kepler Guest Observer Input Catalog that lie in or near the gamma Dor and delta Sct instability strips. Note that we are only requesting long-cadence data, and we are proposing to observe stars that have not yet been observed by Kepler. It is imperative that we not miss this opportunity to observe these stars with Kepler, as it is nearly impossible to discover and monitor the gamma Dor stars with pulsation periods of order one day from the ground. Analysis of Kepler data to date has shown that the long cadence data is also capable of detecting delta Sct frequencies that are more than 1 hour; the properties of the short frequencies can be refined later by short-cadence data later, or by ground-based photometry. We also will perform follow-up observations of the promising hybrid candidates with ground-based spectroscopic observations using the New Mexico State University 1 meter or 3.5 m Apache Peak telescopes to obtain accurate effective temperatures and surface gravities, constrain rotation rates, detect abundance peculiarities, and rule out binarity or star spots as a cause of periodicities. A larger survey of these stars with the high-precision photometry provided by Kepler is essential to help resolve the mysteries surrounding the theoretical model predictions and to realize the potential for asteroseismology of these stars.
MEASURING THE MASSES AND RADII OF THE LOWER MAIN SEQUENCE II: IDENTIFICATION OF NEW ECLIPSING M-DWARFS
Thomas Harrison
We propose to continue to use Kepler to search for new low-mass main-sequence eclipsing binaries and characterize intrinsic M dwarf activity. Recent studies of eclipsing low-mass stars, (which allow the determination of individual masses and radii to better than 1%), have shown that the radii of late-type dwarfs are consistently 10% larger than predicted by stellar models. The cause for this might be enhanced magnetic activity due to their binarity, and thus artificially enhanced rotation rates. If so, such an effect should diminish with increasing semi-major axis and thus period. Unfortunately, only a single known system has a period > 3 days, and thus this hypothesis cannot be tested. Additional eclipsing low-mass dwarfs, especially with long periods, are needed. Kepler is ideally suited to find these long-period systems, whereas ground-based surveys are cadence and/or magnitude limited. We present an optimal sample of 1,200 currently unobserved M dwarfs to monitor for eclipsing systems. We will use NMSU resources at Apache Point Observatory to obtain follow-up photometry and spectroscopy to determine the fundamental parameters of the components in each system in conjunction with the Kepler data. Additionally, we propose to study low-mass star rotation periods, flare rates, and spot cycles for all stars which turn out not to be binaries. In relation to the Kepler Mission and broader impacts, the knowledge of how the radii of low-mass stars depend on their intrinsic properties is critical to accurately determining the radii of transiting planets around such stars. As well, characterizing M dwarf variability at the mmag level is needed to understand how this variability affects planetary transit signatures over time in low-mass systems.
GROUND-BASED FOLLOW-UP AND LIGHT CURVE MODELING OF ECLIPSING BINARIES TO DETERMINE LIMB DARKENING EFFECTS FOR THE KEPLER BANDPASS
We will use NMSU facilities to obtain UBVRI light curves of Algols in the Kepler field of view to ascertain the limb darkening for the broad Kepler bandpass. As we show below, limb darkening strongly affects parameters extracted from exoplanet transits. The Kepler bandpass is very broad, and therefore the derived, mean limb darkening cannot be easily predicted. This is especially true given the fact that limb darkening for normal stars has been shown to be in error by +/-10 - 20%! We have a current program to derive the limb darkening effects for a sample of Algols with a large range of spectral types. To extrapolate our results to the Kepler bandpass we request observations of 15 Algols in the Kepler field-of-view, and support to observe these Algols using NMSU facilities. In this way we can combine our ongoing program on limb darkening measures for long period Algols, with one specifically tied to Algols observed with Kepler, to quantify the limb darkening in the Kepler bandpass.
UNLOCKING NEW DISCOVERY SPACE IN THE MICRO- AND MEGA-FLARE REGIMES ON LOW MASS STARS
Suzanne Hawley
Low mass stars with strong magnetic fields often exhibit energetic outbursts known as flares. Flares are believed to be caused by magnetic reconnection events in the coronae of these magnetically active stars. They occur on timescales of seconds to days, and span more than eight orders of magnitude in emitted energy. We propose to use the NASA Kepler satellite to monitor six low mass M dwarf stars at short (1 minute) cadence for two months each. The sample includes both early and late type M dwarfs, with both very active and relatively inactive magnetic fields. These data will improve the time sampling and duration of flare monitoring observations on this class of stars by more than a factor of 10, providing significantly improved sensitivity to both micro-flares (low energy) and mega-flares (high energy). These data will enable us to (a) sample equal energy flares across the M spectral sequence and therefore test the hypothesis that later type stars produce flares at a much higher rate but lower average energy compared to earlier type stars; (b) characterize the morphology of flare light curves, which are used to constrain the origin of flare emission; (c) provide the first investigation of the correlation between flare rates and underlying starspot coverage; and (d) determine the flaring properties of (relatively) inactive M dwarfs. A robust understanding of flares, including the morphology of their light curves and the rate at which flares of different energy occur is central to the understanding of the magnetic properties of cool stars. In addition, characterizing flare rates, energies and light curves is important for the interpretation of transient signals in surveys such as LSST and Pan-STARRS, and to predict the radiation environment of the habitable zones of exoplanets.
INVESTIGATING THE ORIGIN OF LSP VARIATIONS
Kenneth Hinkle
National Optical Astronomy Observatory
Long secondary period (LSP) variables are so named because they are late type giants with both long period variation and shorter period pulsation. While approximately 25 - 30% of all pulsating AGB stars show LSP behavior there is no known physical cause for the longer period. LSP variables are the only form of stellar variability that is not understood. However, LSP variables are known to obey a period-luminosity (P-L) relation. This limits the possible causes to two causes: binarity and pulsation. Strong arguments can be made against both binarity and radial pulsation. The remaining possibility is non-radial pulsation. While the long period mode fits this violates current interior models. We propose to use Kepler high precision photometry to look for higher order non-radial pulsation modes. Fourier analysis of the light curve should readily identify these modes. If found the techniques of asteroseismology will be applied. In the absence of non-radial pulsations, we will explore the detailed long term light curve to see if it agrees to high precision with models of ellipsoidal variations. Either the binary or the pulsation models allow interesting outcomes. The binary model involves near-planet sized companions with orbits evolved into a very specific configuration. The pulsation model is forbidden by present stellar interior models and will drive now understanding of stellar interior structure.
ABSOLUTE CALIBRATION OF KEPLER USING WHITE DWARFS
Jay Holberg
We propose to use newly discovered white dwarfs together with Cycle 1 white dwarfs in the Kepler Field to help establish the absolute flux calibration of the Kepler observed magnitudes.	The technique employed uses synthetic photometry and the procedures described in Holberg & Bergeron (2006, AJ, 132, 1221), to place Kepler photometry on the Hubble Space Telescope photometric scale. This proposal will be of direct use to astronomers seeking to relate Kepler photometry to familiar astrophysical photometric scales.
FLUX EMERGENCE AND DIFFERENTIAL ROTATION TIMESCALES ON F-M TYPE STARS
Gaitee Hussain
We propose to study differential rotation and flux emergence timescales on 100+ stars, ranging in spectral type from late-F to M in the open cluster, NGC 6866. This cluster is young enough to contain a mixture of both slow and fast rotators. Theories suggest that rapidly rotating active low-mass stars have a different dynamo mechanism compared to slow rotators. We will characterize the activity levels of stars covering a wide range of spectral type and rotation rate. We will exploit the high precision of Kepler to measure surface flows and flux emergence timescales on stars at a range of activity levels and spectral types in order to gain further insight into angular momentum evolution and stellar magnetic activity. We will use custom software and techniques to match chromospheric and surface activity. Our findings will inform and test flux emergence models currently being developed for cool stars.
CHARACTERIZING THE TOP OF THE RED GIANT BRANCH USING KEPLER DROP-LIST STARS
Jason Jackiewicz
We propose to conduct a study of the internal properties of fifty-five stars located near the top of the red giant branch. All of these stars are currently on the Kepler drop list. Program stars have effective temperatures and surface gravities of less than 3600K and log(g) = 1.0 respectively. Project goals are 1) to quantify the range of pulsation spectra found in upper red giant branch stars, 2) to use state-of-the art FAMIAS software to determine the values of several key global and interior properties, and 3) to determine the decay rate (if any) of the observed pulsation modes. Parameters to be measured include masses, ages, metal contents, convective overshoot parameters, hydrogen contents, radii, surface rotations, and rotation profile. Many of the pulsation modes in red giants are thought to be unstable. Observational studies support this assertion, however, the measured decay times range from days to weeks, and even longer time frames are allowed. Since little is known about the long term stability of the oscillations in these stars, and the necessity of removing the longer term pulsations from our light curves, a full year of data is requested.
PHOTOMETRY OF A VARIABLE HOT SUBDWARF STAR IN NGC 6791
Steven Kawaler
Iowa State State University
We propose a one year observation of the unique hot blue star B4 in NGC 6791, one of only a handful of subdwarf B (sdB) stars known to exist in an old open cluster, and the only cluster sdB known to show photometric variability caused by binarity. The goal of these observations are twofold - we expect to observe nonradial pulsations in this star, and plan to study longer period variations caused by its binarity. The primary goal is to confirm our expectation that B4 should show nonradial pulsations, since its temperature and gravity place it within the instability region for g-mode sdB pulsators, where pulsations are seen in about 75% of the stars (Green et al. 2003). The discovery of a pulsator in a well-studied open cluster of known age and metallicity would provide new and unique probes of the pulsation mechanism for the pulsating sdB stars. Because of the faintness of the star, the time scale of the variations (periods of approximately 45 to 90 minutes) and the expected small amplitude of the pulsations, Kepler is the only instrument able to measure these oscillations to the degree of precision needed for asteroseismic analysis. Our secondary goal is based on the fact that this star is already known to be a low-amplitude (2%-9%) variable with a period of 0.8 (or 0.4) days, The proposed observations will provide a high signal-to-noise light curve for analysis of the binary system. From photometry alone, we will be able to constrain the orbital properties of the binary, and the mass and radius of the companion. Subdwarf B (sdB) stars belong to a class of stars that represent the post-helium core flash evolution of low mass stars. They lie at the extreme blue end of the horizontal branch (Teff ~ 25,000 - 35,000K), and are the remnant cores of stars that have experienced the core helium flash while on the RGB. They have extremely thin (and inert) hydrogen shells surrounding a core undergoing helium fusion. The mechanism(s) that produce these stars is/are currently unknown, though leading scenarios include mass transfer in a binary system. Single-star mechanisms have also been proposed and remain viable given the limitations of observables in these stars. Asteroseismic probes of this star, coupled with the additional constraints of cluster membership and the properties of the binary system, should provide important clues about the formation mechanism of the extremely hot subdwarf stars. Because this star is relatively faint (V=17.88, Kepler magnitude 18.27), published ground-based data are insufficient to establish the nature of the known variability or determine the properties of the binary system. Furthermore, ground-based data are insufficient to detect the shorter period variability expected for any pulsations. Only with an extended, uninterrupted time series can we answer these questions, and the Kepler spacecraft is the only instrument capable of providing the needed data. If it shows pulsation, B4 will be a uniquely valuable star - a nonradially pulsating star, in a close binary system, within a cluster. The binary nature will allow mass and perhaps radius determination, the presence in a cluster secures knowledge of its distance, age, and metallicity, and with these constraints the asteroseismology will be tightly constrained.
KEPLER'S DETAILED VIEW ON THE PULSATIONS OF THE RR LYRAE PROTOTYPE AND BLAZHKO STAR RR LYR
Katrien Kolenberg
Though the RR Lyrae stars have been studied for over a century now, several aspects of their pulsations remain ununderstood. An intriguing subclass consists of the stars showing the Blazhko effect, with light curves that are modulated on time scales of typically tens to hundreds of days. Despite numerous studies, the origin of these long-term cycles remains a mystery. Moreover, in several RR Lyrae stars glitches and short-term irregularities in the light curves have been observed. This phenomenon has never been studied in detail. RR Lyr, the eponym and prototype of the RR Lyrae stars, is one of the best studied stars of its class. It is also a well-known Blazhko star with a modulation period of about 39 days (Kolenberg et al. 2006). In photometry of the star spanning over a century, both the pulsation and the Blazhko cycle have shown variations that are too fast to be of an evolutionary nature. On top of this, short-term irregularities have also been reported in RR Lyr. The 33.5 days of photometry of RR Lyr gathered during Kepler's first roll showed the potential of the unprecedented accuracy of Kepler data. On the basis of these preliminary data we already detected previously unseen frequencies (Kolenberg et al. 2010). The nature of the newly detected frequencies and their connection to the Blazhko effect, as well as the small irregularities in the pulsation of RR Lyr, can only be investigated with short cadence data. This would be the first time such a study is undertaken, and no other instrument can explore these previously unseen aspects of the star's pulsation. We propose to observe RR Lyr with Kepler in short cadence during more than two complete modulation cycles (90 days). By observing RR Lyr itself, we will be able to study variations in the Blazhko cycle, and the nature of the additional observed frequencies and their stability. These observations will be a milestone in gaining a better understanding of the pulsations of RR Lyrae stars in general.A better understanding of the Blazhko effect and other deviations from strictly regular pulsation will improve RR Lyrae stars as distance scale calibrators and tracers of galactic history.
DETECTING THE RELATIVISTIC BEAMING EFFECT IN ECLIPSING BINARIES WITH KEPLER
Tsevi Mazeh
We propose to observe a set of known eclipsing binaries in the Kepler field, in order to detect a small periodic intensity modulation with the binary period, due to relativistic effect, never observed so far. The intensity modulation depends on the radial velocity of the two stars, and therefore can be used as photometric radial-velocity measurements, allowing to determine or at least constrain the binary masses.We expect the amplitude of the effect to be of the order of 100 ppm or more. We can detect this effect with 5 sigma significance for stars with non-periodic stellar jitter of 1000 ppm. We apply now for a modest set of eclipsing binaries, so we can establish the ability of Kepler to perform this novel kind of observations.
THE STRUCTURE AND GLOBAL PROPERTIES OF RED GIANT CLUMP STARS
Bernard McNamara
We propose to conduct a targeted study by using Kepler to measure the pulsation properties of 128 red clump stars over the one year period of cycle 2. Since the program stars were selected from the Kepler drop list, they are known to be highly variable. Stars in the red clump are the metal-rich counterparts to the horizontal branch stars. Using the tools of asteroseismology and Kepler light curves, the masses, radii, temperatures, and ages of these stars will be determined. Several interior giant star properties will also be measured. These include: composition gradients, core sizes, and the convective overshoot parameter. A secondary goal is to use Kepler light curves to quantify the pulsation lifetimes. Giant star oscillations are expected to be stochastically excited and then damped, but the damping time frame is disputed. Suggestions range from a few days to several weeks, but it could be much longer.
A CALIBRATION STUDY OF VARIABLE STARS IN THE KEPLER FIELD: CYCLE 2
Kenneth Mighell
We propose to do a calibration study of variable stars in the Kepler Field which will be enable us to produce enhanced data products that will support and extend the broad science goals of the Kepler mission. Our primary objective is to produce proper flux-calibrated astronomical-grade light curves for individual stars that will complement the detrended light curves produced by the Kepler data pipeline. Relying upon the planned calibration efforts of the Kepler Science Team, we plan to produce nearly time-continuous light curves which extend the planned current monthly time base differential light curves to at least a quarterly basis and possibly a time base covering the entire 3.5 year lifetime of the Kepler primary mission. These light curves will have a Y axis value of "Flux" (in ergs/sec) instead of "Relative Flux" (in electrons / cadence) as given in the standard Kepler detrended light curves that are delivered by the Multimission Archive at STScI. This extended time base capability will support Kepler mission efforts to characterize the nature of the host stars of detected planetary candidates; in particular we will be able to gain better insight to the nature of brightness fluctuations over days to months which might be caused by chromospheric activity.
HIGH-PRECISION KEPLER MONITORING OF ACTIVE GALACTIC NUCLEI
Richard Mushotzky
We propose to monitor 20 of the brightest AGN in the Kepler field (V = 11.0-18.7) to obtain the first AGN light curves that uniformly cover time scales of hours to months. Most AGN show significant optical variability on these time scales, which is connected to emission from the accretion disk and thus provides one of the few ways of to study the physics of accretion in these objects. For the 10^6 to 10^9 solar mass black holes thought to power most AGN, one expects time scales ranging from the light-crossing times of minutes to weeks to the thermal time scales of order months to years. Previous optical monitoring was unable to access the critical short time scales due to diurnal and weather-related interruptions and poor photometric repeatability. These uninterrupted, high-precision light curves will yield the first AGN optical power spectral density functions (PSDs) of comparable quality to those obtained in the X-rays. This will allow us to determine the overall shape of optical PSDs, and if they are like X-ray PSDs, we will be able to measure slopes to 0.02-0.1 and detect breaks indicative of a characteristic variability time scale indicative of light-crossing or dynamical time scales in the accretion disk. Based on what is known about the optical variability characteristics of AGN our simulations show that Kepler will represent a breakthrough in this area allowing the determination of precision PDSs for several 10s of AGN. This is directly connected to one of NASA key goals in astrophysics, understanding the nature of black holes and active galaxies.
ASTROMETRY OF STARS & GALAXIES IN THE KEPLER FIELD
Robert Olling
We propose to observe three distinct sets of objects: 1) ninety-one (91) stars that are likely to be within 100 parsec from the Sun, and which have not previously been identified as such [the SN sample], 2) nine (9) K Giant Stars in Kepler's field of view that are part of the SIM-Lite Grid-star Catalog [SGC], and 3) four hundred and sixty three (463) small, nucleated galaxies that we will use to define an Absolute Astrometric Reference system [AAR] and to determine astrometric accuracy. Our science and technical goals for these target groups are as follows. The SN sample will improve the census of stars in the solar neighborhood. Because of their relative proximity, these systems are well-suited for a Kepler-based astrometric search for stellar and sub-stellar companions. Through a study of their positions and motions, we expect to be able to find Brown Dwarfs and long period planets that can be added to the target lists for future missions in NASA's Exoplanet Exploration Program. The SN sample is unique in that it allows both astrometric and RV studies so that masses can be determined unambiguously. The SGC K-giant stars were selected by the SIM program on the presumption that they would not have measurable astrometric wobble. We will evaluate the astrometric and photometric stability of these systems for suitability as astrometric standards for the SIM-Lite mission. This study will be particularly relevant for NASA if the Astro2010 Decadal Committee gives SIM-Lite the go-ahead in NASA's Exoplanet Exploration Program. The AAR sample comprises galaxies as identified in the 2MASS extended source catalog with diameters not exceeding 10 arcsec. We select about ten such small galaxies for each of our stellar targets. As was done for the Lick Proper Motion programs, we will use these slightly extended sources as absolute astrometric standards. We will use methods developed by the VLBA astrometry community to assess the absolute astrometric errors. We will also monitor these galaxies for variability as might occur from low-level AGN activity. We will use the state-of-the art ePSF astrometric methodology as developed by Anderson and collaborators for undersampled point-sources as well as for slightly extended sources.
HIGH-PRECISION MASSES AND RADII OF LOW-MASS ECLIPSING BINARY STARS
Jerome Orosz
We propose to obtain Kepler light curves of 7 long-period low-mass eclipsing binary (EB) targets. By making high-precision observations during the eclipses of these binaries we aim to resolve the long standing discrepancy between the theoretical and observational mass-radius relations at the bottom of the main-sequence, namely that the observed radii of low-mass stars are up to 15% larger than predicted by structure models. It has been suggested that this discrepancy may be related to strong stellar magnetic fields, which are not properly accounted for in current theoretical models. All previously well-characterized low-mass main-sequence EBs have periods of a few days or less, and their components are therefore expected to be rotating rapidly as a result of tidal synchronization, thus generating strong magnetic fields. We hypothesize that the stars in the binaries with longer orbital periods, which are expected to have weaker magnetic fields, will better match the assumptions of theoretical stellar models. By employing Kepler's high-precision photometry we will be able to determine the radius of both components to within a fraction of percent, which thus far has not been done for any low-mass binary with periods longer than a few days.
KEPLER OBSERVATIONS OF MASS TRANSFER ACTIVITY IN DIRECT-IMPACT ALGOL-TYPE INTERACTING BINARY SYSTEMS
Geraldine Peters
We propose a combination of high and low cadence Kepler observations of seven direct-impact Algol-type binaries in the Kepler fields to study the physics of mass accretion in these interacting systems. Included are the identification of a hot accretion spot at the site of the gas stream impact and a determination of its size and longitude, a search for accretion- induced photospheric oscillations, and a search for micro-flaring that might result from variable shocks due to a clumpy gas stream. Since a splash from a direct impact and the radiative energy from hot spots can precipitate systemic mass loss, their existence influences the evolution of close binaries. We expect that a hot spot and micro-flaring will be visible only on the trailing hemisphere of the system. Oscillations should be global, but perhaps of an irregular nature on hemisphere experiencing the impact. Although we have a general understanding of how Algol systems are formed and their evolutionary state, little is known about the details of the mass accretion. We will investigate both short and long-term variability over many orbital cycles to identify unique light curve structure that will provide insight into the physics of mass transfer. Since observing time on the GALEX spacecraft has been approved for two of the systems, UZ Lyr and BR Cyg, we have the opportunity to acquire simultaneous UV and Kepler photometry that will aid in the modeling of mass transfer activity. The Kepler photometry will be analyzed with the latest version of the Wilson-Devinney light curve analysis program. The residual light will be analyzed using standard Fourier techniques. Frequencies found in the residuals will be interpreted with the aid of current asteroseismology software. The project addresses NASA's Strategic Subgoal 3D, Discover the origin, structure, evolution, and destiny of the universe, and search for Earth-like planets, as it will advance our understanding of the evolution of early-type close binary stars.
ECLIPSING BINARIES IN THE OLD OPEN CLUSTER NGC 6791
Ruth Peterson
Astrophysical Advances
We propose 73 photometrically-selected targets with V < 16.6 within 12' of the center of the old, metal-rich open cluster NGC 6791 for Kepler 30-min sequence observations. The goal is to detect eclipsing binaries suitable for determining the masses of the components, through future observations of radial velocities with large ground-based telescopes, and possibly of orbits with SIM. Our targets are giants and subgiants, not main-sequence stars, in order to reduce confusion in the Kepler field and to provide feasible targets for spectroscopy. Towards the center of the cluster, the high stellar densities dramatically increase crowding and cause binaries to be more readily perturbed. Consequently we are including many targets in the outer regions of the cluster, those which fall on the cluster color-magnitude and color-color diagrams defined by the inner members. We need a large target sample to isolate favorable binaries, as some stars will be non-members, only half of the members will be in binaries, many of these will have merged, and only a few of those remaining are useful. Suitable binary systems must not be triple, and should include a giant and a main-sequence turnoff star so that both components can be detected spectroscopically. The components must not have previously exchanged or lost mass. Binary periods must be nearly a year to a few years, so the orientation must be nearly edge-on and the eccentricity will be finite. We expect the proposed observations to yield at least two non-interacting binaries from which both component masses can be obtained. For such binaries, eclipse depths of 10% over a day or more are expected, and are readily apparent from applying standard filters to the pipeline light curves. Radial-velocity curves will be based on echelle spectroscopy analyzed with IRAF, as we have done in our decade-long survey of the brightest NGC 6791 giants with the Lick Hamilton echelle. The effective temperature, gravity, and metallicity of each of the stellar components will be found from theoretical spectral calculations, which now match such strong-lined stars reasonably well thanks to an updated list of line parameters. This work should stringently constrain comparisons of observed color-magnitude diagrams to produce meaningful cluster parameters. Such constraints would have major significance for the validation or refinement of stellar evolutionary tracks at high metallicity, and the derivation of age and metallicity from broadband colors of both individual stars and integrated spectra of old elliptical galaxies, for which NGC 6791 is a critical template.
ULTRA-HIGH PRECISION PHOTOMETRY OF OVERCONTACT BINARY STARS: FUNDAMENTAL PROPERTIES AND EVOLUTION
Andrej Prsa
This proposal focuses on the fundamental properties of overcontact binary stars -- short-period systems where the two main sequence components share a common envelope. Our understanding of formation, evolution and physical properties of overcontact binaries is incomplete, mostly due to the limited data accuracy. Kepler will alleviate this problem, allowing us not only to advance, but to essentially resolve the standing issues that have persisted in the field of close binaries for over 40 years. These are: 1) the formation of overcontact binaries. The two competing theories attribute the tightening of close binary orbits and subsequent coalescence to either a steady angular momentum loss due to tidal and rotational friction, or to interactions with the third body. Kepler's uninterrupted observations will establish the current angular momentum loss, which will enable us to turn back time and compute whether steady angular momentum loss could feasibly cause coalescence; 2) the dominant energy transport mechanism in overcontact binary envelopes. The current standing theory asserts that thermodynamic equilibrium is sustained by the so-called Thermal Relaxation Oscillation (TRO) cycle. In essence, one component overflows its Roche lobe, causing mass transfer on the other component. The transferred mass veils the component completely, blocking the flux, converting it to thermal energy and causing the increase in the radius of the veiled component. Once that component grows over its Roche lobe, the process is reversed. Lately, however, this model has been theoretically shaken by showing that the Coriolis force would cause veiling only in the equatorial regions of the star, thus enabling it to keep radiating energy through the polar regions. Kepler's photometric data accuracy will allow us to directly observe veiling: if only a band covers the star, there will be a discrete jump in its disk brightness at the band boundary, an effect routinely modeled in the field of eclipsing binaries. If such a jump is found, it will have proven that the TRO hypothesis cannot adequately describe the mechanism that sustains the thermodynamic equilibrium; 3) many overcontact binaries show evidence of geometric contact but not thermal contact. The data accuracy so far inhibited our ability to correlate the two, but with the promise that Kepler brings, physical parameters of overcontact binaries will be determined to a sufficient accuracy via modeling to formulate this correlation; 4) since most overcontact binaries show signs of chromospheric activity, we will be able to directly probe differential rotation and limb darkening of severely distorted stars; lastly, 5) we invested significant effort to reformulate the theoretical model backbone so that it withstands Kepler's data accuracy. Our model builds on the Roche constricted three body hypothesis, where stars are considered point sources, surrounded by a massless envelope. This approximation proved adequate for ground-based observations, but Kepler will put the extent of applicability of this model to the test. Any deviation will have strong implications on the eclipsing binary modeling in general. Our study will be based on a carefully selected sample of 50 overcontact binary stars in the Kepler field of different variation amplitudes and orbital periods. Two of those exhibit total eclipses, making them ideal astrophysical laboratories for the focused, in-depth study. For these we propose short cadence observations (half a year each, occupying a single short cadence channel overall), and for the remaining program stars we propose the long cadence mode. Analyzing this sample will not only answer the listed questions, it will also yield physical and geometrical properties of these stars of unprecedented accuracy in a uniform way. Our research team has extensive experience (both theoretical and observational) in eclipsing binary stars and we feel well positioned to conduct this research successfully.
UNDERSTANDING M-TYPE STARS AS EXOPLANET HOSTS: CHARACTERIZING VARIABILITY AT SHORT TIMESCALES
Ignasi Ribas
Institut de Ciencies de l'Espai
Exoplanet research has experienced an exponential growth over the past few years. This is both because of the impressive discoveries made recently and also because of the inherent appeal of the topic. One of the future challenges is the discovery and subsequent characterization of habitable exoplanets. Intensive efforts are being put into advancing towards this goal. A possible shortcut to find a potentially habitable planet is to carry out the searches around low-mass stars (M dwarfs). M-type exoplanet hosts have two major advantages: (1) Because of the lower stellar mass and luminosity, habitable planets are closer in, have shorter orbital periods and hence induce higher amplitude reflex motions on the star; and (2) because of the smaller radius, a transit of a terrestrial planet has a depth of a few per cent and therefore it is suitable for discovery and follow up even from the ground. The search for exoplanets around M-type stars is blooming with new experiments (like the MEarth transit search) and projects for the near future. A critical element to the advancement of this field is to attain a detailed characterization of the targets. This is chiefly because of the inherent stellar activity that affects M-type stars causing both photometric and radial velocity jitter. Such jitter is related to the overall light modulation induced by starspots and to the time variability of their position and properties. Surprisingly, the activity patterns of M-type stars are largely unknown at the required level for exoplanet investigations. We will utilize the Kepler data, with its exquisite precision and time coverage, to obtain the power spectrum of the variability of some 10 bright M-type stars in the Kepler field over timescales from minutes to months. We will investigate the photometric variations to understand the variability patterns (including starspots and other activity-related phenomena) and define the best strategy to mitigate their effect in photometric or spectroscopic transit searches from the ground. In addition, we will collect data that will be central to the missing overall characterization of M-type stars as potential exoplanet hosts.
DYNAMO PARAMETERS IN YOUNG SUNS: A KEPLER STUDY OF DIFFERENTIAL ROTATION AND ACTIVE REGION DECAY RATES IN NGC 6811 (1 GYR) AND NGC 6819 (2.5 GYR)
Steven Saar
The formation and evolution of a magnetic dynamo is an integral part of the evolution of low-mass stars and the basis for a wide variety of observable phenomena in such stars. Yet despite decades of observational and theoretical study, we do not have a predictive dynamo model even for the best studied case - the Sun. A limiting factor has been the difficulty of making observations that can properly constrain key physical properties, such as differential rotation and turbulent diffusivity, important to understand and model the stellar dynamo. We propose to take advantage of Kepler's superb photometry to measure differential rotation as well as the growth and decay rates of surface active regions (a proxy for diffusivity) for 235 known members of the open clusters NGC 6811 (1 Gyr) and NGC 6819 (2.5 Gyr). The proposed study will more than triple the existing differential rotation measurements for dwarf stars over a wide range of masses, with the added advantages of having fixed metallicity and well determined ages. This work will also yield the first extensive survey of the growth and decay rates in homogeneous samples of dwarfs. We will also explore the frequency of magnetic grand minima at younger ages. Our measurements will add important new constraints on magnetic dynamos in stars, permitting better, more physically realistic models.
AGE-SENSITIVE DETACHED ECLIPSING BINARIES IN OPEN STAR CLUSTERS NGC 6791 AND NGC 6819
Eric Sandquist
Age is difficult to measure extremely precisely for stars other than the Sun. In the field being observed by Kepler, the stars of the open clusters NGC 6791 and NGC 6819 are the ones that can be most precisely age-dated. However, different methods provide ages that differ significantly. We propose an effort to bring methods of stellar age determination into agreement through the use of Kepler data for these star clusters. Here we focus on the use of masses and sizes measured from weakly-interacting eclipsing binary star systems in the clusters. Massive stars run out of hydrogen fuel at their centers before less massive ones, and start to change rapidly in size - for such rapidly evolving stars, measurements of both mass and radius that are precise to 1% can lead to ages precise to 10% and better. Further, mass and radius measurements are conceptually simple to derive from observations, and avoid complicating effects like uncertainties in distance and reddening. High precision age measurements from this and other methods will make these star clusters important testbeds for models of stars and stellar populations in galaxies.
BRIGHTNESS VARIATIONS FROM THE ACCRETION DISK IN CH CYGNI
Jennifer Sokoloski
The aim of the proposed Kepler program is to determine whether the accretion disks around white dwarfs are fundamentally similar to those around neutron stars and black holes. We will accomplish this goal by generating the first power spectrum of optical brightness fluctuations from an accreting white dwarf to span a large enough range of frequencies to reveal all the features typically seen in the power spectra of X-ray fluctuations from X-ray binaries. Since this broad power spectrum will need to cover time scales ranging from less than a minute to months with an unprecedented level of sensitivity, we will combine long-cadence observations with the Kepler satellite with fast optical photometry from ground-based telescopes. As the accretion disks around white dwarfs primarily emit in the optical, whereas the accretion disks around neutron stars and black holes primarily emit in the X-rays, we will determine the degree to which white-dwarf and X-ray binary disks are similar by comparing the optical power spectrum of a specially selected accreting white dwarf --- CH Cygni--- to the well-studied X-ray power spectra of neutron-star and black-hole X-ray binaries. The accreting white dwarf in the symbiotic binary CH Cygni is ideal for this study because it has a long enough orbital period that there will be no confusion between brightness variations that are due to the behavior of the accretion disk and those that are due to the orbit of the binary. The power spectra of X-ray binaries (in particular low-mass X-ray binaries, or LMXBs) display a characteristic set of features. These features include quasi-periodic oscillations and broad components that can be fitted by Lorentzian functions. As the compact objects in LMXBs have weak or non-existent magnetic fields, these features in the power spectra are not due to magnetic accretion. Instead, they are thought to be related to the accretion disk itself, with possible connections to the dynamical, thermal, and viscous time scales at the inner edge of the disk. They have properties and relationships that hold whether the accreting compact object is a neutron star or stellar-mass black hole, and recent observations suggest that supermassive black holes and white dwarfs might also produce the same pattern of variations. If our Kepler observations confirm that the accretion onto an object for which general relativity is not needed to describe the trajectories of matter and radiation near its surface, such as a white dwarf, has the same variability properties as accretion onto a relativistic object such as a black hole or neutron star, there will be several major implications. The more than two decades of research on LMXB variability will become relevant to accreting white dwarfs, and the myriad studies of disks around white dwarfs in cataclysmic binaries will become relevant to LMXBs. Moreover, models for the X-ray variations from LMXBs that invoke general relativity, as the most popular models do, and the possibility of using the features in LMXB power spectra to probe strong gravity, will be called into question. Observing CH Cygni with Kepler is technically challenging because the source is very bright. However, we have made plans to use a custom aperture to overcome these difficulties. Tackling these technical challenges is worth the effort because achieving our science goal will have broad implications, and Kepler is the only instrument that can obtain a long enough continuous light curve with high enough sensitivity to accomplish this goal.
VARIABILITY OF AN AVERAGE SYMBIOTIC BINARY - STHA 169
We propose to determine whether or not the symbiotic star StHA 169 contains a hidden accretion disk by studying its sub-mmag-level flickering properties that only Kepler has the sensitivity to detect. Symbiotic stars are wide binaries in which a white dwarf (WD) accretes from a red-giant companion. It has proved difficult to determine exactly how mass is lost by the red giant (Roche-lobe overflow, spherical wind, or "focused wind"?) and how it is accreted by the white dwarf (via an accretion disk or direct impact?). Most cataclysmic variables (CVs, in which the mass donor is a Roche-lobe filling main-sequence star), on the other hand, are known to accrete via a disk. A variety of observational techniques (including eclipse mapping and Doppler tomography) have not only confirmed the presence of the disk beyond a shadow of a doubt in non-magnetic CVs, but also revealed the detailed physics of the disk. For symbiotic stars, ground-based fast optical photometry has revealed stochastic brightness variations (termed "flickering") at tens of percent level in a few objects. This phenomenon, which is routinely observed in CVs, is a well-known signature of the accretion disk; the power spectrum of this disk flickering has a characteristic steep powerlaw shape at high frequencies. However, this successful determination that accretion proceeds via an accretion disk has been limited to a small subset of symbiotic stars. In the vast majority, no flickering is seen with a typical upper limit of about a few tenth of a percent. Does this mean that the majority of symbiotics do not actually contain disks, contrary to simple expectations ? Another possibility is that symbiotic stars do contain disks, but that the amplitude of disk flickering is reduced due to the presence of some other constant source of light. In other words, the disks are hidden. We can distinguish between these possibilities by using the phenomenal sensitivity of Kepler to detect mmag-level and even sub-mmag-level flickering in an ordinary symbiotic star. Here we propose a one-month fast-cadence Kepler observation of an ordinary symbiotic star, StHA 169 (the only such system in the Kepler field-of-view), to detect and characterize its flickering. The Kepler sensitivity is sufficiently high that a non-detection flickering with a steep powerlaw power spectrum will imply that a disk does not exist in this system, and perhaps in many other ordinary symbiotic stars. Since symbiotic stars are known to be the progenitors of at least some type Ia supernovae, understanding how they accrete could also shed light on the generation of cosmologically important supernovae.
CATACLYSMIC VARIABLES IN THE KEPLER FIELD
Martin Still
NASA Ames Research Center
Cataclysmic variables provide the cleanest available natural laboratories to investigate the physical behaviour of accretion disks. The timing capabilities and sensitivity of Kepler are well matched to the timescales and amplitude of accretion disk variability in these sources. This combination provides an unprecedented opportunity to test and refine the paradigms of stellar accretion with high-precision, uniform data containing no diurnal or seasonal gaps. We propose a multi-faceted observational and modeling program that puts our current understanding of accretion disks to the test and has the potential to measure the spatial structure of model-dependent disk parameters. Kepler observations of cataclysmic variables will impact profoundly our understanding of accretion disk dynamics and the nature of astrophysical viscosity. The proposed observations will provide an outstanding astrophysical legacy for the Kepler mission.
CHANDRA-SELECTED X-RAY SOURCES IN THE KEPLER FIELD
The Kepler mission has a finite lifetime. *If* there is no mission extension in 2012, there will be only three Guest Observer cycles before the spacecraft is switched off. We expect the Kepler archive to provide a rich heritage but the onus is upon the community to choose Kepler targets now that maximize the impact of Kepler in the future. There are many ways to attack target selection, but the one we propose here is to add new Kepler targets to the observing list that have been X-ray selected. Based upon the ROSAT all-sky survey, the Kepler field contains thousands of X-ray sources. The majority of these have an undetermined nature but experience suggests that the sample is comprised mostly of magnetically active stars, accreting stars and background quasars. All such sources would be premium targets for an instrument with Kepler's strengths - uniform cadence, long uninterrupted data sequences and high photometric precision. We propose a conservative study in cycle 2 of the best-localized, unidentified X-ray sources from the Chandra Source Catalog, with the potential goal of expanding the survey greatly in cycle 3.
TEMPORAL ANALYSIS OF RV TAURI AND SEMI-REGULAR VARIABLES USING KEPLER
Donald Walter
RV Tauri stars are luminous, supergiant variables with periods of pulsation that are sometimes predictable and sometimes not. Their lightcurves show alternating deep and shallow minima with a primary period of variability in the range of 30-150 days while their spectra vary across several spectral types. Semi-regular (SR) variables show some periodicity, but are even less regular than RV Tauri stars. RV Tauri and other SR variables occupy the region of the HR Diagram between the Cepheid instability strip to the left and the long period Mira types to the right. The evolutionary status of these objects is uncertain and an adequate explanation of the changes in their spectra and light curves is lacking. The presence of a number of RV Tauri stars in the Local Group of galaxies and their potential use in distance calculations adds cosmological significance to better understanding their luminosities and other characteristics. Studies to date are constrained by the limitations of ground-based data from AAVSO and the literature (e.g. Pollard et. al., 1996, MNRAS, 279, 949). Our own, modeling efforts (Cash et. al, 2009, AIP Conference Proceedings, CP1170, 146) include curve-fitting of the AAVSO data using Fourier and other methods to determine the periods of pulsation in the light curves and to examine the stability of the calculated periods. We propose to use Kepler to observe approximately 15 of these objects in its field of view through several of the stellar phase cycles over a time span of 12 months. Using Kepler's long cadence exposures of 30 minutes will provide unprecedented temporal detail and photometric precision. In order to provide insight into the underlying physical processes of these stars, we will combine the Kepler photometry with our modeling techniques and ~800 high signal-to-noise, archival spectra we have taken at the Coude-Feed telescope at Kitt Peak National Observatory over the past decade. This proposed research is relevant to the stated objective of the solicitation for the acquisition and analysis of new data that uses the high-precision photometry of Kepler for asteroseismology and other variability studies of Galactic sources. This in turn fits NASA's mission to pioneer the future in scientific discovery, in particular the Astrophysics Division's Focus Area for Stars that includes understanding how stars form and evolve. The NASA Strategic Plan and Goals for 2006-2016 include Sub-goal 3D to which this proposal is relevant "Discover the origin, structure, evolution, and destiny of the universe, and search for Earth-like planets."
UNDERSTANDING BLAZAR VARIABILITY THROUGH KEPLER
Ann Wehrle
Space Science Institute
We propose to monitor four flat spectrum radio quasars (blazars) and one powerful radio galaxy, Cygnus A, to search for variability on timescales comparable to the light crossing time of the accretion disk around the central supermassive black hole and the base of the relativistic jet.	We want to see if some optical variability in quasars is due to a bright feature in the accretion disk as it approaches the last stable orbit, or if it is due to inhomogeneities in the jet, possibly in a helical structure. When the quasars are in quiescent, faint states, a quasi-periodic light curve indicates an accretion disk origin, and provides a dynamical means of measuring a lower limit to the mass of the supermassive black hole which may be compared to those derived by other methods, such as the shape of X-ray iron K$\alpha$ lines and stellar velocity dispersions. When the quasars are in bright states, then long-lived quasi-periodic oscillations (QPOs) are very probably from helical features in the jets, but if several different short-lived QPOs are seen in one quasar, then the emission is probably coming from turbulence behind a shock. If during a faint state, instead of QPOs, we detect aperiodic variations, including high and low breaks in the power spectrum density (PSD), then we may obtain the physical scales of the inner and outer edges of accretion disks and hence the BH mass. Aperiodic variations during a high state, with breaks in the PSD, could yield the smallest and largest physical scales corresponding to light travel times, modulo the Doppler factor, in the relativistic jet. Kepler is ideally suited to the necessary measurements by delivering highly stable photometry continuously on timescales from minutes to days.