text:
\section{Introduction}
Polars or AM Herculis binaries are strongly magnetic cata\-clysmic
binaries. The
white dwarf's magnetic field locks both stars in synchronous rotation and
prevents the formation of an accretion disk. Instead mass transfer occurs
via an accretion stream which is thought to follow initially a ballistic
trajectory and later governed by the magnetic field, which leads the matter
along magnetic field lines to the polar regions of the white dwarf. Most of
the gravitational energy is released there, although some dissipative energy
loss is expected to occur all along the stream, in particular in the coupling
region where the stream is forced to leave the orbital plane.

The stream manifests itself observationally in mainly three ways, (A) by
so-called absorption dips observed in IR, optical or X-ray light curves
(provided the inclination is high enough and the observer and the accretion
spot are (blue in color)
located on the same side of the orbital plane), (B) by residual
emission during eclipses of the white dwarf, and (C) by
strong, asymmetric and variable emission lines (H, He\,{\sc i}, He\,{\sc ii}
and other high-ionized species) at optical and UV wavelengths
(provided the system is in a high accretion state). The dips mentioned in (A)
occur, if the line-of-sight crosses the out-of-plane parts of the
stream. They are caused by photoelectric (at X-ray wavelengths), grey or
free-free (at optical/IR wavelengths) absorption and are richly structured,
indicating a highly fragmented stream. An overview of relevant data and
analysis was given recently by Watson (1995).
Phenomenon (B) is less studied because only a handful of eclipsing polars
are known and the numbers of photons
collected at eclipse which certainly arise from the stream are rather few,
hence, model\-ling of these events is widely missing in the literature, but
nice observational data meanwhile have been obtained e.g.~for UZ For (Schmidt
et al.~1993), WW Hor (Beuermann et al.~1990) and HU Aqr (Schwope et al.~1995).
The emission lines (C) have attracted by far most attention because their
occurence
is one of the `classical' identification criterion. A diverse
appearance is reported in the literature, they may consist of broad, narrow,
high- and medium-velocity as well as (quasi-)stationary components, all
with different radial velocity amplitudes and systemic velocities. These
components may have a different appearance when a specific system is
re-observed occasionally (see e.g.~the review of Mukai 1988). The mini\-mum
distinction usually made discerns between a narrow line attributed to the
secondary star and a broad underlying component whose origin is assumed
to be somewhere in the accretion stream (see e.g.~Liebert \& Stockman 1985,
who have shown that for the systems known at that time the radial velocity
amplitude of the narrow line lies between that expected for the $L_1$ and
the center of mass of the companion).
Later on, Rosen et al.~(1987)
have presented high-resolution spectra of V834\,Cen and distinguished
4 subcomponents, which were thought to originate at different parts of the
accretion stream and the secondary star. Schwope (1991) and
Schwope et al.~(1991, 1993a)
made use of repeated measurements of the narrow line in order to derive
long-term ephemerides of the secondary star for
the non-eclipsing systems QQ\,Vul, MR\,Ser and V834\,Cen.
Recent attempts to locate the
line emission in polars applied tomographic techniques to data obtained
on VV\,Pup and RX\,J0515.6+0105 (Diaz \& Steiner 1994, Shafter et al.~1995).

HU~Aqr\ is a system which has all of the observable features of the stream
mentioned, at least occasionally. It was discovered
independently by British and German astronomers during their
optical identification programmes of ROSAT WFC and PSPC sources detected
in the corresponding sky surveys (Schwope et al.~1993b, Hakala et al.~1993).
Since it was the brightest eclipsing polar with the most extended eclipse
at that time (meanwhile surpassed by RX\,J0515.6+0105) it attracted immediate
interest. We initiated an intensive optical follow-up study using
4 telescopes simultaneously and performed spectroscopy with high and low
spectral resolution, high-speed photometry simultaneously in UBVRI-colours
as well as standard one-channel photometry using a V-filter. All data
have good signal/noise-characteristics and provide a comprehensive
database suitable to reach deeper insight into the kinematics and
accretion processes of the whole class. Here we present as a first paper
in an upcoming row our results of high-resolution spectroscopy.

\section{Observations and reductions}
HU~Aqr\ was observed with the 3.5m-telescope and Cassegrain double-beam
spectrograph
(TWIN) at Calar Alto, Spain, on August 17/18, 1993. Both arms of this double
beam spectrograph (beamsplitter at $\sim$5500\AA ) were equipped
with low-noise Tek-CCDs (1K, pixel size 24$\mu m$) as detectors. We used
a 1\farcs 8 wide slit thus matching the approximate size of the seeing disk.
The spectral coverage was 4180--5070\AA\ in the blue arm, 7450--8770\AA\ in
the red arm. The red spectra were taken in order to search for the photospheric
Na-doublet from the secondary star. Since HU~Aqr\ was in a high accretion state
at that time this attempt failed. We, therefore, restrict our analysis to
the spectra taken in the blue arm. The grating used there with 1200 grooves per
mm yielded a FWHM spectral resolution of $\sim$1.6\AA\ in the center, and
$\sim$3\AA\ at the edges of the spectra.

\begin{figure}
\psfig{figure=fig1_ps,width=88mm,bbllx=48mm,bblly=60mm,bburx=158mm,bbury=172mm,clip=}
\caption[meanlc]{\label{mean_lc}
{\it (upper panel)} Phase-averaged optical B-band lightcurve of HU Aqr
for the period August 16-18, 1993. The counts of HU Aqr
were reduced to that of
a simultaneously observed nearby comparison star. Binsize of the lightcurve
is 3.75 sec (2000 phase bins).
{\it (lower panel)} Phase coverage of the individual trailed spectra of length
30 min (no. 1-6) and 12.5 min (no. 7).
}
\end{figure}

In order to avoid velocity smearing a radial velocity study of an AM~Herculis
binary requires a phase
resolution of $\Delta \phi \simeq 0.05$ (Mukai 1988), hence $\sim$6$^m$
for a binary like HU~Aqr\ with period $P_{\rm orb} = 125^m$.
The time overhead between subsequent exposures at the TWIN, on the other hand,
is $\sim$5$^m$ due to CCD-readout,
data transfer and storage of the large-format images from both
arms of the spectrograph, which prevents a dense phase coverage.
We resolved the time conflict by trailing the object along the slit
while exposing. Individual exposure times were 30$^m$ with a
nominal trailing rate of 15 sec/pixel, which, taking into account the
size of the seeing disk of $\sim$2~pixels, finally yielded a time resolution
of $\sim$30 sec or 0.004 phase units. A total of 6 spectra with 1800\,s
and one with 750\,s integration time were obtained yielding full-phase
coverage.
Wavelength calibration of the flatfielded
and bias-subtracted two-dimensional images was performed
using Helium-Argon arc spectra taken every hour, a small shift of the arc line
pattern on the CCD due to flexure of the spectrograph was accounted for during
reduction of the data.
Cosmic-ray removal was achieved by median filtering small regions of size
$5\times 5$ pixels around suspected cosmics which were identified
by Laplace-filtering of the raw images.
Sky-subtraction was performed afterwards in the usual manner by fitting
polynomials to CCD-columns above and below the region exposed to the
target star.

\begin{figure*}[t]
\psfig{figure=fig2_ps,width=18cm,bbllx=20mm,bblly=111mm,bburx=191mm,bbury=227mm,clip=}
\caption[meanspec]{\label{mean_spec}
Mean-orbital high-resolution spectrum of HU~Aqr\ on August 17, 1993, after
subtraction of the continuum and after correction to zero velocity (narrow
emission  line). The same data are shown twice, in the bottom panel on
an expanded intensity
scale in order to facilitate identification of faint lines
}
\end{figure*}

Next, the spatial coordinate of individual pixels along the slit
had to be transformed to time or orbital phase. We defined start and end
of the exposure as coniciding with those pixels lying most nearly to half
intensity between average sky- and (sky+object)-level in an adjacent
10 pixel surrounding. This resulted in a trailed spectrum with
116 or 117 pixels for an 1800 sec exposure, slightly different
from the 120 pixels expected from the nominal trailing rate of the telescope.
Since the lightcurves extracted from the trailed spectrograms
and the simultaneous photometry yielded no systematic offset, we assigned
the discrepancy to a slightly incorrect trailing rate of the telescope and
estimate the timing accuracy of the spectrum in a single CCD-row to be better
than 15 sec.

Simultaneously to our spectroscopy we obtained high-speed photometric data
(0.5 sec resolution) using the 2.2m-telescope also located at Calar Alto which
was equipped with the MCCP (Barwig et al.~1987). The MCCP allows
monitoring of the target star, a compa\-rison star and the nearby sky
simultaneously in UBVRI colours. In order to correct slit-losses
and guiding errors of our trailed spectra, we first flux-calibrated them
using observations of the white-dwarf standard star Wolf 1346, folded them
through the response of the MCCP B-filter, binned the MCCP-data in 15 sec
time bins according to the timing of our trailed spectra and finally
multiplied individual rows of the trailed spectra using the ratio of both light
curves (photometric, spectroscopic).

Final steps of data reduction included normalization of the spectra
by subtracting low-order polynomial fits to the continuum and phase-folding
into 100 phase bins using our updated photometric ephemeris of eclipse center
\begin{equation}
T_{\rm ecl} = {\rm HJD} 244\,8896.543707(27) + E \times 0.086820446(9).
\end{equation}

\section{Results and analysis}
\subsection{The lightcurve}
In Fig.~\ref{mean_lc} (upper panel) we show the mean light curve in the B-band
measured with the MCCP at the 2.2m-telescope. In the lower panel of the
diagram the phasing and phase coverage provided by our trailed spectra
is displayed.
The most remarkable features of the light curve are: a) the deep eclipse
of the white dwarf and the accretion spot by the late-type companion
star, b) a pronounced pre-eclipse dip centered on phase
$\phi_{\rm ecl}$ = 0.88, c) a double-humped shape outside eclipse and dip, and d)
strong QPO/flaring outside eclipse and dip.
A detailed discussion of the light curves will be given elsewhere, in the
context of our present analysis the interesting features are the eclipse
and the dip.
\begin{figure*}[th]
\psfig{figure=fig3_ps,width=18cm,bbllx=10mm,bblly=123mm,bburx=193mm,bbury=227mm,clip=}
\caption[trailed_spec]{\label{trailed_spec}
Trailed, continuum-subtracted, high-resolution spectrum of HU~Aqr\ on
August 17, 1993, computed by phase-averaging the individual trailed spectra
using 100 phase bins.
The dynamic range of this grey-scale image with wavelength running along
the abscissa and phase along the ordinate was set appropriately to
emphasize weak lines.
The behaviour of the strong lines is better visible on the zoomed
representations of Fig.~\ref{trailed_lines}
}
\end{figure*}

The eclipse is two-stepped with the first step being
very steep ($\sim$3\,sec) followed by a more shallow second step with ingress
time of about 120\,sec. All four steps have different heights. We
identify the obscured sources of light with the hot accretion plasma
on the white dwarf emitting cyclotron radiation (steep ingress/egress)
and the accretion stream (shallow ingress/egress). Both emitters radiate
anisotropically which gives the explanation for the different stepsizes
at ingress and egress. The eclipse of the white dwarf itself is not
clearly resolved in our data.
We measured the length of the eclipse as the difference
between the maxima in the first derivative
of the lightcurve at ingress and egress
phase to be 584.6\,sec. This value represents the eclipse length of the
accretion spot on the white dwarf surface. The spot is nearer to the secondary
star than the center of mass of the white dwarf CM$_{\rm wd}$.
The eclipse of the CM$_{\rm wd}$ is shorter by a factor $\alpha_{\rm CM}/
\alpha_{\rm spot}$ with $\alpha$ being the opening angle of the secondary
star as seen from the CM and the spot, respectively. The minimum value of
this correction factor is 0.9792 ($\Delta t_{\rm ecl,CM} = 572.4$\,sec),
calculated for the extreme (and therefore unlikely) assumptions of inclination
$i = 90\degr$ and spot co-latitude $\beta = 0\degr$ (spot in the orbital
plane).

The Gaussian shaped dip is centered on $\phi_{\rm ecl}$ $= 0.882 \pm 0.003$ (deflection
angle $d = 42.5\degr\pm 1.1\degr$ with respect to the line joining both stars)
and has a FWHM $=0.034\pm 0.001$ phase units. A $\pm 2\sigma$-range around
dip center (95\% of the absorbed flux) spans a range $d = 32\degr - 53\degr$.
The emission lines are not obscured at dip phase (see Figs.~\ref{trailed_spec}
and \ref{trailed_lines}), only the cyclotron continuum is absorbed. The dip
is therefore naturally explained as obscuration of the accretion spot
by the transient accretion stream as in other polars (see Sect.~1).
Since HU~Aqr\ is a system with a high inclination, dip center and width mark
exactly the location and extent of the coupling region in the orbital plane.

\subsection{The mean orbital spectrum}
In Fig.~\ref{mean_spec} we show the mean-orbital, continuum-subtracted,
radial-velocity-corrected spectrum of HU~Aqr. For radial-velocity correction
we used the $\sin$-fit to the narrow emission line of He\,{\sc ii}\,$\lambda$4686 (see below).
The profiles of the emission lines in Fig.~\ref{mean_spec} therefore show
a spiky narrow emission line atop broad line wings.
We can identify the emission lines normally found in AM Herculis binaries,
as e.g.~the Balmer lines H$\beta$ and H$\gamma$, the prominent lines of
neutral (He\,{\sc i}\,$\lambda\lambda$4387, 4471, 4713, 4921, 5015)
and ionized Helium (He\,{\sc ii}\,$\lambda$4686), but find in addition several features
not easily recognized in other systems. We note in particular the partially
resolved C{\sc iii}/N{\sc iii}-structure at 4635-4650,
C{\sc ii}\,$\lambda$4267, a second line of
ionized He (He{\sc ii}\,$\lambda$4541) with an additional unidentified
fainter line in its red wing and Mg{\sc ii}\,$\lambda$4481 in the red wing
of He{\sc i}\,$\lambda$4471.
\begin{figure*}[t]
\begin{center}
\begin{minipage}[]{85mm}
\psfig{figure=fig4_hgam_ps,width=85mm,bbllx=35mm,bblly=83mm,bburx=181mm,bbury=236mm,clip=}
\end{minipage}
\begin{minipage}[b]{9mm}
\end{minipage}
\begin{minipage}[]{85mm}
\psfig{figure=fig4_he1_ps,width=85mm,bbllx=35mm,bblly=83mm,bburx=181mm,bbury=236mm,clip=}
\end{minipage}

\vspace{0.5cm}
\begin{minipage}[]{85mm}
\psfig{figure=fig4_he2_ps,width=85mm,bbllx=35mm,bblly=83mm,bburx=181mm,bbury=236mm,clip=}
\end{minipage}
\begin{minipage}[b]{9mm}
\end{minipage}
\begin{minipage}[]{85mm}
\psfig{figure=fig4_hbet_ps,width=85mm,bbllx=35mm,bblly=83mm,bburx=181mm,bbury=236mm,clip=}
\end{minipage}
\end{center}
\caption[trailed_lines]{\label{trailed_lines}
Grey-scale representation of trailed, continuum-subtracted, high-resolution
spectra of the strong emission lines of HU~Aqr\ on
August 17, 1993 (zoomed representation of Fig.~\ref{trailed_spec}).
Phase runs along the ordinate from bottom to top, wavelength has been
transformed to velocity using the rest wavelengths of the specified lines.
The dynamic range for all representations is for all lines approximately
between 0 and 80\% of maximum intensity.}
\end{figure*}

The C{\sc iii}/N{\sc iii}-complex is resolved into three lines, a single line
of N{\sc iii} ($\lambda 4634.2$) and two blends of N{\sc iii}
($\lambda\lambda 4640.6, 4641.9$)
and C{\sc iii} ($\lambda\lambda 4647.4, 4650.3, 4651.5$). The lines of C and N
are of comparable strength. According to Williams \& Ferguson (1983) the
N{\sc iii}-lines are probably excited by continuum fluorescense. This
does not apply to C{\sc iii}\,$\lambda$4650 or to
C{\sc ii}\,$\lambda$4267 which do not couple directly to the ground states
via electric dipole resonance lines. Whereas C{\sc ii}\,$\lambda$4267 may
be excited by dielectronic recombination no final conclusion was
reached by Williams \& Ferguson
about the probable excitation mechanism of the C{\sc iii}-lines, apart
from the general statement, that `some selective excitation mechanism is
operative for this line'. We would like to note simply here that
this special excitation
mechanism does not require other conditions regarding
density, temperature and external radiation field than are required for
excitation of
the other transitions of the high-ionization species
found in the spectrum of HU~Aqr, since the kinematics and structure of
all high-ionization lines seem to be the same.

Three lines of the He{\sc ii}-Pickering series ($n=4$)
lie in our spectral window at
$\lambda\lambda$4859.32 ($m=8$), 4541.59 (9), and 4338.67 (10). The line
at 4541\AA\ is clearly resolved whereas the other two blend with
H$\beta$ and H$\gamma$. The wavelength-difference between the H-Balmer
and the He{\sc ii}-lines is 2.01\AA\ and
1.80\AA , respectively, which is at the limit or below our spectral
resolution at the specified wavelengths. From our low-resolution spectra
we estimate the flux ratio between the non- or weakly-blended
lines at 4541.59\AA\ ($m=9$) and 5411.52\AA\ ($m=7$), $F_{5411}/F_{4541} \simeq
1.9$, and interpolate to estimate the contribution of He{\sc ii}\,$\lambda$4859
to H$\beta$, which is of the order of 10\%, but variable as a function
of phase.  H$\gamma$ itself is stronger than H$\beta$ and the blending
He{\sc ii}-line ($m=10)$ is weaker than that at H$\beta$, hence we expect
a much weaker contamination of H$\gamma$.

The Balmer lines show an inverted Balmer decrement with
$I(H\beta )/I(H\gamma ) = 0.86$. The value for optically thin `case B'
recombination is $\sim$2.12 (Pottasch 1984),
hence the Balmer lines are significantly optically
thick. Although also He{\sc ii}\,$\lambda$4686 is not optically thin (see
below), the fact that this line is only weakly
blended (by He{\sc i}\,$\lambda$4713 and C{\sc iii}\,$\lambda$4650) and that
our spectral resolution is highest just at this line makes it the most
suitable one in our spectra for detailed investigations, but before doing so we
take a general look at the trailed spectrograms.

\subsection{Trailed spectra}
In Figs.~\ref{trailed_spec} and \ref{trailed_lines} we show the
phased-averaged trailed spectra in overview (weak lines emphasized) and for
the strong lines H$\beta$, H$\gamma$, He\,{\sc i}\,$\lambda$4471, He\,{\sc ii}\,$\lambda$4686\
in detail with a phase resolution of 100 phase bins.
In Fig.~\ref{trailed_spec} it can be seen that the
phase intervals centered on $\phi_{\rm ecl}$ = 0.11, 0.46, and 0.78
which were covered only once during our observations
have higher noise in the continuum, the effect on the S/N in the
strong lines is nevertheless negligible.
All emission lines have the same structure and can be subdivided
into three emission line components (best visible in He\,{\sc ii}\,$\lambda$4686). Most striking is
a narrow emission line (henceforth referred to as NEL), which is most
prominent around $\phi_{\rm ecl}$$ = 0.5$ and which has zero radial velocity at conjunction
of the secondary star. This component is naturally explained as being
of reprocessed origin from the illuminated hemisphere of the secondary star,
seen here in unprecedented clearness. The second component has a more transient
nature, it is a relatively narrow line, moving in a zig-zag manner from
maximum recessional velocity ($>1000$\,km\,s$^{-1}$ ) around eclipse phase to large
negative velocities ($<-1500$\,km\,s$^{-1}$ ) around $\phi_{\rm ecl}$ = 0.45. This component
is brightest in the phase intervals $\phi_{\rm ecl}$$ = 0.20-0.25$ and $0.70-0.75$, around
those phases where it crosses the NEL. We refer to this component as
high-velocity component HVC. The third component is a broad underlying
one visible throughout the whole orbital cycle (outside eclipse), with
maximum blueshift around $\phi_{\rm ecl}$$ \simeq 0.40$ which we refer to as broad base
component BBC. The HVC and the BBC must originate in the stream.
\begin{figure}[th]
\psfig{figure=line_lcs_ps,width=88mm,bbllx=27mm,bburx=196mm,bblly=34mm,bbury=151mm,clip=}
\caption[line_lcs]{\label{line_lcs}
Variation of the integrated line flux of the four main emission lines
as a function of phase. Shown are from top to bottom the light curves for
H$\gamma$ (histogram), H$\beta$ (polygon), He\,{\sc ii}\,$\lambda$4686 , and He\,{\sc i}\,$\lambda$4471.
}
\end{figure}

Although the four main emission lines have the same general appearance
differences exist in details. This concerns the width of the NEL,
which is broader in the H-Balmer lines than in the He-lines, and
the lightcurves of the lines (brightness variation as a function of phase).
The width of the NEL of the different lines is addressed in the
next section (3.4); the lightcurves are shown in Fig.~\ref{line_lcs}
(integrated flux over the wavelength interval used for display
in Fig.~\ref{trailed_lines}). The intensity of the stream components
dips to a minimum at phase $\phi_{\rm ecl}$ $\simeq 0.53$, and is generally stronger
before than after this dip. This asymmetry is generally stronger for
the low-ionization lines H$\gamma$, H$\beta$, He\,{\sc i}\,$\lambda$4471 with flux ratios
$F(\phi < 0.53)/F(\phi > 0.53) = 2.09, 2.14, 2.02$, respectively,
than for the high-ionization
He\,{\sc ii}\,$\lambda$4686-line with the corresponding flux ratio of 1.54.

A likely explanation for the brightness variation of the HVC, which is
pronounced only at certain phases,
lies in the illumination geometry and significant optical thickness of the
stream in the low-ionization lines. The Balmer lines and He\,{\sc i}\,$\lambda$4471
are bright when the stream is seen from its concave, that is its
illuminated side
(see Fig.~\ref{stream_geo} for a sketch of the geometry). The convex,
non-illuminated side of the stream visible after $\phi_{\rm ecl}$$ = 0.53$
lies in its own shadow and is therefore much fainter than in the less
optically thick He\,{\sc ii}\,$\lambda$4686-line.

\subsection{The width of the NEL in He- and H-lines}
The trailed spectrograms of the Balmer lines (in particular their NELs)
look somewhat blurred or diffuse when compared with the He-lines.
Here we investigate, if this is caused by the weak blending lines of
the He{\sc ii}-Pickering series mentioned above.
The mean width (full width at half maximum FWHM) of the four strongest
emission lines (H$\gamma$, He\,{\sc i}\,$\lambda$4471, He\,{\sc ii}\,$\lambda$4686, H$\beta$) in the phase interval
$=0.50-0.56$ (NELs intensive, stream components relatively faint) is
$(4.19\pm0.18)$\AA, $(2.74\pm0.15)$\AA, $(2.47\pm0.07)$\AA, and
$(4.34\pm0.12)$\AA\, respectively.
The spectral resolution of arc lines at the wavelengths of our lines
is 2.33\AA, 1.92\AA, 1.67\AA, and 1.76\AA, which yields intrinsic widths
of the NEL
of 3.48\AA, 1.95\AA, 1.82\AA, and 3.97\AA. The He-lines have the same
widths within the errors (1.95 vs.~1.82\AA ), whereas the Balmer lines
are significantly broader.

We have synthesized blended line profiles of H$\beta$ plus
He{\sc ii}$\lambda 4859$ assuming the same intrinsic line width for both
lines of 1.82\AA \ (that of the He\,{\sc ii}\,$\lambda$4686 -line) and a maximum relative intensity
of 20\% of the He-line. After folding with the instrumental resolution at
H$\beta$, the resulting unresolved line had a FWHM of 3.8\AA \
(observed 4.34\AA ). We conclude that the NELs of the Balmer lines are
intrinsically broader than those of the He-lines. Using the same scheme
of synthesizing line profiles, we could estimate the width of the H$\beta$-NEL
to be $\ga 3.5$\AA . Below we show that the width of the He{\sc ii}-line
is explained by velocity broadening introduced by the range
 of orbital velocities over the illuminated hemisphere of the
secondary star. Hence, each line which originates in that region should have
at least this width. If we assume that the observed excess width of H$\beta$
is caused by thermal Doppler broadening, we would need
temperatures in excess of
$2\times 10^6$\,K in order to reflect the observations. This temperature,
corresponding to coronal temperatures, is unbelievably high for a line
originating in a (quasi-)chromosphere. The canonical temperature for the
Balmer-line emission region in active M-stars is $10^4$\,K and the observed
line widths at H$\alpha$ are about $\la 2$\,\AA \ (Giampapa et al.~1982,
Worden et al.~1981). This is also true for irradiated atmospheres
of dMe stars although our knowledge of this very complex process is very
poor (see e.g.~Cram 1982).
A more likely explanation seems to be that the observed
line width reflects orbital motion of a more extended Balmer line region,
perhaps some kind of wind/mass outflow component that co-rotates with the
secondary star. An even simpler possibility is `saturation broadening' due
to large optical depths in the Balmer lines.

\subsection{Gaussian deconvolution of He\,{\sc ii}\,$\lambda$4686 }
The conventional approach to investigate the emission line structure
in polars is fitting of Gaussians. Due to the lack
of spectral and temporal resolution often a distinction between
a broad and a narrow component is made and only two Gaussians are used
but sometimes up to four (Rosen et al.~1987).
We followed that approach and performed a triple-gaussian fit for the NEL,
the HVC and the BBC in an iterative fashion.

\begin{figure}[th]
\psfig{figure=vrad_ps,width=88mm,bbllx=15mm,bburx=193mm,bblly=141mm,bbury=270mm,clip=}
\caption[vrad]{\label{vrad}
Radial velocities of the three subcomponents of He\,{\sc ii}\,$\lambda$4686, determined
by fitting Gaussians with fixed widths to the phase-binned spectra
shown in Fig.~\ref{trailed_lines} (NEL: open and filled circles, HVC:
crosses, BBC: squares). The solid line is a $\sin$-fit to the NEL-data
shown with filled symbols, the dashed lines are smooth interpolations
for the HVC and BBC used as guess-values for subsequent iterations
}
\end{figure}

In a first step we fitted three Gaussians to each of the phase-binned
spectra shown in Fig.~\ref{trailed_lines} while fixing the widths (FWHM)
of the NEL and the HVC at 2.5\AA and 4.5\AA, respectively. This gave
very good estimates for the radial velocities, and good estimates for the
line intensities and the FWHM of the BBC. The latter displayed no distinct
orbital variation, instead it showed an erratic scatter of 1.5-2\,\AA \ around
$11.5$\,\AA . Results for the radial velocities thus obtained are shown
in Fig.~\ref{vrad}. The fits gave unreliable results for the line intensities
and for the wavelengths at those phases where two components are crossing
each other. This happens at phases $\phi_{\rm ecl}$$\sim$0.23 and $\sim$0.70
between NEL and HVC and at $\phi_{\rm ecl}$$\sim$0.35 between HVC and BBC. In order to
provide input guess values for a second iteration,
the phase-dependent radial
velocities were approximated by smooth curves, a sinusoid for the NEL,
spline-curves for the HVC and BBC.
The sinusoid and the splines are shown as solid and dashed curves in
Fig.~\ref{vrad}, the sine curve was calculated using only the data points
drawn with filled symbols.
In a second step we fitted all individual 15 sec spectra in the trailed
spectrograms, where these fits were restricted to a small
range around the interpolated guess values and
the NEL was fixed on the input guess values.
Similarly, the phase-binned trailed spectrogram was fitted
a second time using these smoothed guess values from the first step but
allowing the FWHM to vary freely within certain ranges.

\begin{figure}[th]
\psfig{figure=lc_3comp_ps,width=88mm,bbllx=25mm,bburx=175mm,bblly=30mm,bbury=270mm,clip=}
\caption[lc_3comp]{\label{lc_3comp}
Light curves of the three subcomponents of He\,{\sc ii}\,$\lambda$4686, determined
by Gaussian fits to individual trailed spectra as described in the
text. The uppermost panel represents the summed light from the accretion
stream, the lowest that from the secondary star. The solid line in the
lowest panel is the result of a model calculation, described in Sect.~3.6
}
\end{figure}

The results of these subsequent steps of the fitting procedure,
the intensity variations of the three emission line components and the
variation of the FWHM of the NEL, are shown in Figs.~\ref{lc_3comp} and
\ref{fwhm_nel}. In Fig.~\ref{fwhm_nel} we show only those data, for which
the NEL
could be clearly separated from the HVC. In Fig.~\ref{lc_3comp} we also show
the summed lightcurve of HVC and BBC representing the light from the
stream.
The lightcurve of the BBC can be roughly described as a two-stepped function,
with constant brightness before and after superior conjunction
of the secondary. It is brighter by $\sim$50\% during first half of the
orbital cycle than during the second half. The hump centered on $\phi_{\rm ecl}$$\simeq
0.35$ is an artefact of the fitting procedure, the excess light there is
missing in the HVC-lightcurve, the same may apply to the less pronounced
hump at phase 0.82. The lightcurve of the HVC has two pronounced humps
separated by $\sim$0.5 in phase with the first hump centered on
$\phi_{\rm ecl}$$\simeq$0.22. The sum of both, the HVC and the BBC, shows two smooth humps.

The lightcurve of the NEL finally is single-humped. This
component is brightest around superior conjunction of the secondary, but
has a remarkable asymmetry with respect to phase 0.5. It is brighter
during first part of the orbital cycle, with maximum brightness
at $\phi_{\rm ecl}$ = 0.46. In some of our fitting experiments, depending on chosen
input values and caging of parameters, the brightness of the NEL
became even compatible with zero at phases later than 0.75 but it has
$\sim$20\% of the peak flux at the symmetric phase $\phi_{\rm ecl}$$ = 0.25$.

The width (FWHM) of the NEL is largest at and slightly after superior
conjunction ($\phi_{\rm ecl}$$ = 0.5$), reaching
a maximum value of about 2.45\AA . We were prevented from really measuring
the width for phases later than $\sim$0.63 due to the decreasing brightness
of the NEL and interference with the other line components.

The radial velocity variation  of the NEL is in excellent agreement with a
$\sin$ curve. The fit assuming a circular orbit for the data points shown
with filled symbols in Fig.~\ref{vrad}, $v(\phi) = v_{\rm sys} + K^\prime_2
\sin (2\pi (\phi - \phi_0))$, yields $v_{\rm sys} = -7.8\pm 1.4$\,km\,s$^{-1}$ ,
$K^\prime_2 = 293.5 \pm 1.3$\,km\,s$^{-1}$ , and $\phi_0 = 0.016 \pm 0.001$.
There is a small additional systematic uncertainty not larger than
$\sim$3\,km\,s$^{-1}$ for $K^\prime_2$ dependent on the data points included in the
fit. If we correct the systemic velocity to the solar system barycenter,
$\Delta v = -3.5$\,km\,s$^{-1}$, it becomes $v_{\rm sys} = -11.3 \pm 1.4$\,km\,s$^{-1}$ .
We refer to the radial velocity amplitude as $K^\prime_2$ (instead
of $K_2$) because it represents the velocity of the center of light
of the illuminated hemisphere instead of the center of mass.

Glenn et
al.~(1994) have presented some 10 high-resolution spectra of H$\alpha$
obtained when the system probably was in a somewhat different state
of activity. Probably due to the lack of phase-resolution they discern
between a broad and a narrow component only and derive $v_{\rm sys} = 83\pm
44$\,km\,s$^{-1}$, $K = 244 \pm 44$\,km\,s$^{-1}$, and $\phi_0 = 0.04 \pm 0.04$,
respectively, for their NEL.
The results of both studies are compatible with each other
only at the 2$\sigma$-level, hence we cannot completely rule out real
changes of the emission line structure.
Glenn et al.~have described the broad component
of H$\alpha$ also with a sinusoid. Given our higher-quality data we cannot
use such a simple approach.

Both of our stream components show maximum
recessional velocity around eclipse, the full amplitude of the HVC is
$\sim$2000\,km\,s$^{-1}$, that of the BBC $\sim$1400\,km\,s$^{-1}$.
Neither the HVC nor the BBC display a radial
velocity curve which can be described by a simple mathematical function.
An  analysis of these components
requires a different approach, which is presented below as tomogram analysis.
If one, nevertheless, e.g.~for comparison with the Glenn et al.~analysis,
fits a sinusoid to the radial velocity data of the BBC, $v(\phi ) = \gamma
+ K \sin (2\pi (\phi - \phi_0 ))$, one gets $\gamma = 3 \pm 10$\,km\,s$^{-1}$,
$K = 534 \pm 15$\,km\,s$^{-1}$, and $\phi_0 = -0.32 \pm 0.01$. Again, these values
are compatible with the Glenn et al.~analysis at the 1--2$\sigma$ level.
One question which is left open here in particular is,
whether the two components HVC and BBC originating in the stream
really reflect emission from two separate regions, as it appears,
or whether instead the emission all along the stream naturally produces
skewed profiles
simply due to optical depth, projection and curvature of the stream.
The conventional approach of deconvolution using Gaussian fits, however,
reveals very important information for the interpretation of the tomograms
as far as e.g.~intensity variation is concerned.

The asymmetrical shape of the lightcurve of the NEL, the non-zero
velocity at eclipse and the non-vanishing phase offset $\phi_0$ are
pronounced and require an interpretation. It appears likely that all
three features are related to the same origin, an asymmetric illumination
of the secondary star.

\subsection{A reprocessing model for the NEL}

The skewness of the lightcurve of the NEL is significant. The sole explanation
for such an asymmetry is to assume an asymmetric illumination of the secondary
star. Similar asymmetries, although mirrored with respect to the axis of
symmetry, have been observed by Beuermann \& Thomas (1990) in the
nova-like UX UMa-system IX Vel and by Hessman (1989) in the dwarf nova IP Peg.
The likely mechanism for the asymmetry there
is significant irradiation from the hot spot where the accretion stream
impacts on the disk. Since this lies on the leading side of the secondary
the trailing side is less irradiated and consequently fainter. Such an
explanation cannot work in an AM Her binary, since the source of irradiation
is bound to the surface of the white dwarf.

A related type of asymmetry has been discovered in NaI absorption lines
of AM Her itself by Southwell et al.~(1995) and Davey \& Smith (1996).
These authors detect flux deficits on the trailing side of the secondary
in the NaI absorption lines caused by stronger heating of the trailing
hemisphere, and explain the necessary shielding of the leading side
by absorption in the accretion column near the white dwarf, which points
to the leading side in AM Her.

We have synthesized line profiles originating from the illuminated
hemisphere of the secondary star using the method as outlined in
Horne \& Schneider (1989) and Beuermann \& Thomas (1990). In this model
the Roche lobe surface is covered by a set of discrete surface elements. The
flux incident on each surface element is calculated assuming a point source
located at the position of the white dwarf. Lightcurves and line profiles
are synthesized by summing contributions from all surface elements visible
at a given phase. At this stage we allowed for optically thin emission,
being proportional to the incident flux, as well as for optically thick
emission, where this flux was weighted with the projected surface of the
element in concern. No further line broadening mechanism than velocity
broadening over the illuminated Roche surface and the instrumental broadening
were taken into account.
We calculated a series of these profiles as a function
of phase and shielding. We took the simple view of describing shielding
by a weighting factor for each surface element of the leading side
which was constant for the whole hemisphere. We performed such calculations for
three values of the mass ratio $Q = M_{\rm wd}/M_2 = 3, 4, 5$ assuming that
the secondary follows the ZAMS mass-radius relationship given by
Caillault \& Patterson (1990) (in that case the mass of the secondary is
$M_2 = 0.146$\,M$_\odot$ and only very weakly dependent on mass ratio)
and for $Q=2.5, M_2 = 0.35$\,M$_\odot$, as motivated by our tomogram
analysis. The orbital inclination $i$ was chosen according to the
$q-i$-relation for the observed length of the eclipse (see Fig.~\ref{qi_rel})
as $i = 80\degr, 82\degr, 85\degr, 90\degr$, respectively, for $Q = 2.5, 3,
4,$ and 5.

\begin{figure}[th]
\psfig{figure=nel_mod_k2_ps,width=88mm,bbllx=27mm,bburx=187mm,bblly=60mm,bbury=230mm,clip=}
\caption[nel_k2]{\label{nel_k2}
Results of model calculations for the NEL: Shown are the relation between
radial velocity amplitude, systemic velocity and phase shift obtained from
sine fits to synthetic NEL-profiles as a function of mass ratio and
shielding of the leading hemisphere of the secondary star. The numbers
designate the mass ratio $Q = M_{\rm wd}/M_2$.
The large open
squares connected with solid lines are data computed in the optically thick
mode, the small open squares connected with dashed lines are data computed
in the optically thin mode (shown only for $Q = 5$) and the small circles
are optically thin data for $Q = 2.5$ with a massive secondary of $M_2 =
0.35$\,M$_\odot$. Shielding increases by 10\% between the data points starting
with no shielding at right. The large filled squares are observed data.
}
\end{figure}

\begin{figure}[th]
\psfig{figure=nel_mod_skew_ps,width=88mm,bbllx=22mm,bburx=190mm,bblly=95mm,bbury=192mm,clip=}
\caption[nel_skew]{\label{nel_skew}
Results of model calculations for the NEL: Shown are the relation between
skewness ($I(\phi > 0.5) / I(\phi < 0.5)$) and phase of peak intensity
of the NEL-lightcurve for a mass ratio $Q=5$ and varaible shielding of the
secondary star. As in Fig.~\ref{nel_k2}, shielding grows from right to left
in 10\%-steps and the larger symbols represent optically thick models. The
filled square is the observed value with estimated uncertainties.
}
\end{figure}

\begin{figure}[th]
\psfig{figure=fwhm_nel_ps,width=88mm,bbllx=22mm,bburx=190mm,bblly=95mm,bbury=192mm,clip=}
\caption[fwhm_nel]{\label{fwhm_nel}
Full width at half maximum FWHM of the NEL
transformed to velocity at the He\,{\sc ii}\,$\lambda$4686 -line as a function of phase.
The filled squares are observed data, the lines are model curves calculated
assuming different mass ratios, mass of secondary star, optical thickness
and shielding (see text for details). The dotted line at bottom indicates
the instrumental resolution.
}
\end{figure}

The synthesized profiles were subsequently analyzed in the same manner
as our observed spectra but first their spectral resolution was degraded
to a FWHM = 107\,km\,s$^{-1}$ as observed.
Then single Gaussians were fitted to determine the central wavelength.
Afterwards sine curves were fitted to the modelled radial velocity data,
taking into account only data from those phase intervals which were used
also to determine the observed radial velocity curve.  The results
of this procedure are shown in Figs.~\ref{nel_k2} (parameters of radial
velocity curves) and \ref{fwhm_nel} (FWHM vs.~phase)
together with the observed data.
The modelled radial velocity curves are not exact sinusoids, but the deviation
is negligible for the phase intervals in concern.
Two families of model curves are shown in Fig.~\ref{fwhm_nel}. The upper
four curves are calculated for $Q=2.5, M_2=0.35$\,M$_\odot$, the lower four
for  $Q=5, M_2=0.146$\,M$_\odot$ (the other models with $M_2= 0.146$\,M$_\odot$
but smaller $Q$ are undistinguishable from that with $Q=5$).
The solid lines are optically thick models,
the dashed and dotted lines optically thin. The upper curve of each pair
is for no shielding, the lower curve for 60\% shielding.

In addition to the line profiles lightcurves for the reprocessed lines
as a function of phase were generated. They show a distinct asymmetry
in the required manner, which was parametrized using (a)
a skewness defined as ratio of fluxes $F(\phi > 0.5) / F(\phi
< 0.5)$ and (b) the phase of maximum intensity. Since these parameters
are negligible functions of the mass ratio (they depend only on the adopted
shielding), we show in Fig.~\ref{nel_skew} only one set of model data for
$Q = 5$ and optically thin and thick modes, respectively, together with
the parameters derived from the observed lightcurve of the NEL.

The models and data shown in Figs.~\ref{nel_k2} and \ref{nel_skew}
suggest consistently a mass ratio $Q \simeq 5$, optically thick emission
and an effective shielding of the leading side of the secondary star by
60\%. Lightcurves for the optically thick and thin models were shown also
by Horne \& Schneider (1989), where it can be seen that the thin models
predict a plateau around $\phi_{\rm ecl}$ = 0.5. This happens when always the same numbers
of surface elements are visible for a distinct phase interval. Such a plateau
is not observed in HU Aqr and we conclude from all the detailed comparisons
between our models and the observed data, that the NEL is non-negligibly
optically thick.

The fit is not completely satisfactory for the variation
of the FWHM. While the low-$Q$, high-$M_2$ model predicts too high
values for the FWHM for most orbital phases (upper four curves) the model
with $Q=5$ predicts somewhat too small values, at least if one takes shielding
into account and uses the optically thick models. In addition, shielding
moves the phase of maximum FWHM from $\phi_{\rm ecl}$ = 0.5 towards smaller values
whereas the observed FWHM peaks only at $\phi_{\rm ecl}$$ \simeq 0.5-0.55$.
We note, however,
that the FWHM is the least well determined quantity among all
those used here for comparison between observation and models and we
do not regard the deviation between observation and simulation
as a severe problem.

\subsection{Tomogram analysis of the four main emission lines}

In this section we investigate the trailed spectrograms shown in
Fig.~\ref{trailed_lines} using a
tomographic inversion technique known as filtered backprojection and
described e.g.~by Robinson et al.~(1993). Making use of such an inversion
technique implies that any emission not observed at rest wavelength of a
line is regarded as shifted due to the Doppler effect and the backprojection
from the observers $(v,\phi )$-space to the original $(v_x, v_y)$-plane
thus makes use of the whole line profile (instead making use of
only e.g.~width, intensity
or center). The interpretation of such maps is mostly done by comparison
with computer-generated schematic drawings of the possible locations
of line emission in the binary using as input parameters only the velocites
of the two stars of the binary.

The computation of a predicative Doppler-tomogram (or Doppler-map or shortly
map)
requires a large number of
projections (high phase resolution) and a high spectral resolution.
Our dataset, in particular the trailed spectrogram of He\,{\sc ii}\,$\lambda$4686,
is unique in this respect. The tomograms shown as grey-scale images
in Fig.~\ref{tom_grey} and as contourplots in Fig.~\ref{tom_cont} have a
velocity sampling of 5\,km\,s$^{-1}$ \ for He\,{\sc ii}\,$\lambda$4686 \ and 20\,km\,s$^{-1}$ \ for the other lines.
Two features in the maps are striking, a bright spot at velocities
$v_x \simeq 0-30$\,km\,s$^{-1}$, $v_y \simeq 290$\,km\,s$^{-1}$ \ and
 a cometary tail linked to it and extending
to $v_x \la -1000$\,km\,s$^{-1}$\ at $v_y \simeq 0$\,km\,s$^{-1}$. A third feature appears
as faint smeared blotch in the lower left quadrant of the
maps. Since this blotch has a low contrast in Fig.~\ref{tom_grey} only we show
in Fig.~\ref{tom_stream} the Doppler map of those emission components of
He\,{\sc ii}\,$\lambda$4686 \
attributed to the accretion stream. It was computed by subtracting the
Doppler image of the NEL from that of the complete profile and shows
two main features, the cometary tail and the blotch below it.

\begin{figure*}[t]
\begin{center}
\begin{minipage}[]{85mm}
\psfig{figure=fin_hg_q4_ps,width=85mm,bbllx=34mm,bblly=94mm,bburx=194mm,bbury=249mm,clip=}
\end{minipage}
\begin{minipage}[b]{9mm}
\end{minipage}
\begin{minipage}[]{85mm}
\psfig{figure=fin_he1_q4_ps,width=85mm,bbllx=34mm,bblly=94mm,bburx=194mm,bbury=249mm,clip=}
\end{minipage}

\vspace{0.5cm}
\begin{minipage}[]{85mm}
\psfig{figure=fin_he2_q4_ps_new,width=85mm,bbllx=34mm,bblly=94mm,bburx=194mm,bbury=249mm,clip=}
\end{minipage}
\begin{minipage}[b]{9mm}
\end{minipage}
\begin{minipage}[]{85mm}
\psfig{figure=fin_hb_q4_ps,width=85mm,bbllx=34mm,bblly=94mm,bburx=194mm,bbury=249mm,clip=}
\end{minipage}
\end{center}
\caption[tom_grey]{\label{tom_grey}
Doppler maps of the four main emission lines of HU~Aqr\ computed by
filtered backprojection of the trailed spectra shown in
Fig.~\ref{trailed_lines}. The velocity resolution for the H$\gamma$-,
He{\sc i}-,
He{\sc ii}-, and H$\beta$-lines is 161, 129, 107, and 109\,km\,s$^{-1}$, respectively,
at the origin and 173, 143, 124, 126\,km\,s$^{-1}$ \ at $v = 1000$\,km\,s$^{-1}$.
The overlay shows the shapes of the secondary
star and the accretion stream in Doppler coordinates for an assumed
mass ratio of $Q = M_{\rm wd}/M_2 = 4$.
}
\end{figure*}

Backprojection transforms sine curves to points, the bright spot
thus corresponds to the NEL and represents the irradiated secondary star.
For the He\,{\sc ii}\,$\lambda$4686-line we compare the position of the spot in the Doppler map
with the results of our Gaussian fits. The spot appears at $v_x = 30$\,km\,s$^{-1}$
and $v_y = 283$\,km\,s$^{-1}$ .
The
offset of the spot with respect to the symmetry axis $v_x = 0.0$ reflects the
obscuration of the leading (left) side. The ratio of the velocity components
corresponds to the measured phase offset $\phi_{\rm 0,sin}$
of the radial velocity curve $\phi_{\rm 0,dop} = (2\pi)^{-1}
\arctan (v_x/v_y) = 0.017$,
in good agreement with $\phi_{\rm 0,sin} = -0.016$. The velocity amplitude
$K^\prime_{\rm 2,dop} = \sqrt{v_x^2 + v_y^2} = 285$,
however, is lower than found from the sine fit to the
radial velocity curve $K^\prime_{\rm 2,sin} = 293.5$\,km\,s$^{-1}$. This might be
caused by deviations of the true line profiles from Gaussian curves. We see
such deviations pronounced in our modelled line profiles in the optically thin
approximation and they are present too but less pronounced in the optically
thick models (for an illustration see Horne \& Schneider, 1989, their
Fig.~12). We have checked the hypothesis
by comparing radial velocities measured (a) by sine fitting
radial velocity curves and (b) by 2D-Gaussian fitting in tomograms of our
modelled profiles.
We indeed find differences of the required type
of the order 3--8\,km\,s$^{-1}$ depending on mass ratio
and optically thin/thick approximation. An additional small bias towards
lower velocities of the observed peak in the tomogram is likely due to the
underlying cometary tail. So we regard both methods to be in
agreement. The maps calculated for our synthesized NEL-profiles show
that even with our low spectral resolution (with respect to the width of the
NEL which is not well sampled) we should have seen a triangle-like structure
in the Doppler map sketching the heated `nose' of the secondary star if
the emission happens in the optically thin  approximation. In the optically
thick approximation the modelled tomogram yields only a slightly elongated
structure, very similar to what is observed.

\begin{figure}[th]
\psfig{figure=tom_stream_ps,width=88mm,bbllx=29mm,bburx=194mm,bblly=60mm,bbury=207mm,clip=}
\caption[tom_stream]{\label{tom_stream}
Doppler map of the stream components of He\,{\sc ii}\,$\lambda$4686 computed by sutracting the
Doppler image of the NEL from the Doppler image of the whole line
profile. In order to emphasize the  blotch at $(v_x,v_y) \simeq
(-400,-300)$\,km\,s$^{-1}$, we adopted a linear intensity
scale between 5\% and 60\% of the peak intensity.
}
\end{figure}

The Roche lobes shown as overlays in Fig.~\ref{tom_grey} have all the same
size thus facilitating a comparison of the four emission lines. The
Roche lobes were calculated for a mass ratio of $Q = M_{\rm wd}/M_2 = 4$.
According to the larger widths of the NELs of the Balmer lines discussed
in Sect.~3.4 the corresponding spots are more smeared than those of the
Helium lines. In addition, emission is more concentrated towards the
equator of the Roche lobe in the Balmer lines. All spots except that in the
map of H$\beta$ are bright on the trailing side. The H$\beta$-spot has
maximum intensity at $v_x \simeq 0.0$\,km\,s$^{-1}$ \ and a longish extension
inclined by 135\degr\ towards negative $(v_x,v_y)$-velocities. The radial
velocity amplitudes of the NELs of He\,{\sc i}\,$\lambda$4471, H$\gamma$ and H$\beta$ as measured
in the tomograms are $v = 284, 313, 312$\,km\,s$^{-1}$, respectively. The value for
He\,{\sc i}\,$\lambda$4471 \ agrees with that of He\,{\sc ii}\,$\lambda$4686, both values for the Balmer lines agree with
each other but are significantly higher than those for the Helium lines.

The cometary tail connected to the secondary star in the tomogram is the
horizontal accretion stream. It is the Doppler image of the HVC
as can be seen directly by mapping only this component singled out using
the Gaussian fits. Again this feature appears most brilliant in the
map of He\,{\sc ii}\,$\lambda$4686. Its location and curvature
in the map are sensitive to the velocities of the stars in the binary and,
hence, to the masses
and below we will give mass estimates relying on the
assumption that the ridge of light exactly reflects the location of the
trajectory of the stream (approximated in the usual manner as
single particle trajectory, Lubow \& Shu 1975, freely falling in the
gravitional potential).

\begin{figure*}[ht]
\begin{center}
\begin{minipage}{87mm}
\psfig{figure=he2_cont_q25_ps,width=80mm,bbllx=40mm,bburx=198mm,bblly=97mm,bbury=251mm,clip=}
\end{minipage}
\begin{minipage}{87mm}
\psfig{figure=hg_cont_q5_ps,width=80mm,bbllx=40mm,bburx=198mm,bblly=97mm,bbury=251mm,clip=}
\end{minipage}
\end{center}
\caption[tom_cont]{\label{tom_cont}
Contour plots of the Doppler maps for He\,{\sc ii}\,$\lambda$4686\ (left) and H$\gamma$ (right)
shown in Fig.~\ref{tom_grey} with 11 equidistant contours between 0\% and
100\% of the peak intensity.
The rhombus at $(v_x, v_y) \sim (-400,-300)$\,km\,s$^{-1}$\ indicates
the center of BBC emission, the small circle and
the cross give the loci of the centers of mass of the white dwarf and the
secondary star for the assumed mass ratios of $Q = 2.5$ (left diagram) and 5
(right diagram). Shown are the
shape of the secondary star, the ballistic trajectory (horizontal stream,
upper left quadrant) and the part of the stream which has left the orbital
plane (vertical stream, lower left quadrant).
}
\end{figure*}

The third component in the Doppler-map, the diffuse blotch in the lower left
quadrant, can be identified with the BBC in the trailed spectrogram.
This again became evident by mapping the BBC alone which was isolated
using the Gaussian fits (the corresponding center of emission of the BBC
is marked by a rhombus in Figs.~\ref{tom_grey} and \ref{tom_cont}).
The blotch represents emission from the vertical stream.

We have modelled the location of all components in the tomogram in a
manner described e.g.~by Marsh \& Horne (1988) but included in addition a
magnetic drag influencing the trajectory of the stream. The results are
shown for two extreme cases of the mass ratio in Fig.~\ref{tom_cont} ($Q=2.5$
and 5, respectively) and for an intermediate value of $Q=4$ in
Fig.~\ref{tom_grey}. The
corresponding picture in positional coordinates is shown in
Fig.~\ref{stream_geo}. In Fig.~\ref{view_fwd} we show the geometry of the
stream as seen by a hypothetic observer at the white
dwarf.

The shape of the secondary star projected onto the orbital plane is the
same in position and Doppler coordinates, though rotated by
90\degr\ in the Doppler coordinates because the orbital velocity
vectors are perpendicular to the position vector.
Our stream starts at the inner Lagrangian point $L_1$ with no initial
width.
The stream then follows a single particle trajectory (Lubow \& Shu 1975)
in the
Roche-potential down to the interaction region between magnetosphere and
accretion stream. The location and size of this stagnation region
is determined from the phase and the phase width
of the absorption dip (Fig.~\ref{mean_lc}).
In Figs.~\ref{tom_cont} to \ref{view_fwd}
we show three trajectories with turn-off points adjusted to reflect the
center and width of the stream (distance to center is $\pm 2\sigma$ of
Gaussian fitted dip). There the stream leaves the orbital plane
as it couples onto field lines. We assumed no dissipation to occur in the
interaction region. The abrupt re-orientation of the stream
happens in a small spatial region, but produces a large jump in velocity from
$\sim$(-1100,0) to $\sim$(-400,-300) in $(v_x,v_y)$-space. The stream then
follows the field lines of an assumed dipolar field.
The field axis was fixed at
colatitude $\beta  = 25\degr$ measured with respect to the rotation axis
and azimuth $\Psi = 40\degr$ with respect to the line joining both stars.
The former value derives from the observed motion of cyclotron lines in
low-resolution spectra (Schwope et al.~1996, in preparation), the latter one
from the phase of the optical/X-ray bright phase center.

We have chosen a model with $Q = 4$ ($K_1 = 87$\,km\,s$^{-1}$, $K_2 = 350$\,km\,s$^{-1}$)
for the overlay in Fig.~\ref{tom_grey} which gives a fairly good
representation of the four lines and their subcomponents regarded there.
We note, however, that the HVC-emission of the He\,{\sc ii}\,$\lambda$4686-, He\,{\sc i}\,$\lambda$4471-, and H$\beta$-lines
is concentrated below the line defined by the model,
whereas that of the H$\gamma$-line
is concentrated above the model line. We find excellent agreement between
the HVC-ridge of He\,{\sc ii}\,$\lambda$4686 and the trajectory for a mass ratio of
$Q = 2.5$ ($K_1 = 147$\,km\,s$^{-1}$, $K_2 = 367$\,km\,s$^{-1}$)
and good agreement for H$\gamma$ using a mass ratio of $Q = 5$
($K_1 = 77$\,km\,s$^{-1}$, $K_2 = 384$\,km\,s$^{-1}$) (Fig.~\ref{tom_cont}).

We see in the tomogram that
significant broadening takes place all along the horizontal stream, which is
not reflected by our model. This is due to the simplicity of the model which
does not take into account any potential broadening mechanism as e.g.~the
finite width of the stream and its optical thickness.

\begin{figure}[t]
\psfig{figure=stream_geo_ps,width=88mm,bbllx=27mm,bburx=195mm,bblly=126mm,bbury=236mm,clip=}
\caption[stream_geo]{\label{stream_geo}
Scheme of the accretion geometry in HU~Aqr \ projected onto the orbital plane for
an assumed mass ratio $Q = 5$. Shown are the loci of the center of mass
(cross), the white dwarf (circle) and the secondary star (cross at right)
as well as the Roche-lobes of both stars. Matter leaves the secondary star
at the $L_1-$point and follows a ballistic trajectory. Three field lines
connecting the stagnation region and the white dwarf are shown, the region
in between is densily dotted. One additional field line (dashed line) connects
the inner Lagrangian point with the white dwarf. The region between this line
and the dense vertical stream, where the accretion curtain is located,
is dotted lightly.
}
\end{figure}
It is
somewhat surprising that we cannot detect emission from the stream at really
high velocities ($> 700$\,km\,s$^{-1}$) close to the white dwarf ($v_{\rm ff} \simeq
4000$\,km\,s$^{-1}$). This may reflect the effects of a high degree of ionization
and small radiating surface of the stream at high velocities.
Possible effects which in addition may contribute to the
low velocities in the BBC (and its Doppler image, the blotch)
are (a) a slightly incorrect
continuum subtraction thus removing faint emission at high velocities,
and (b) emission not only from the accretion stream
but also from the accretion curtain,
hence from matter leaving the plane all along the horizontal stream. This
matter is
thought to be responsible for shadowing of the leading side of the secondary
star and its re-emission has not been regarded so far. The turn-off points
of such trajectories lie closer to the $L_1$ and the jumps from the HVC- to
the BBC-region in the map are smaller thus closing the expected gap.
One sees also that the observed large width of the BBC is introduced naturally
by the models due to the simple fact that coupling happens along the
trajectory over a significant distance and the jumps from the HVC- to the
BBC-region adjust correspondingly. In principle, so-called `gamma-smearing'
may contribute to the observed width of the BBC in the Doppler map (Diaz \&
Steiner 1994). Gas with velocity perpendicular to the orbital plane $v_z$
produces a shift $\gamma = v_z \cos i$. The effect of this is to blur the
corresponding feature in the Doppler map over a ring of radius $\gamma$
centered at its usual position. If we assume $v_z = 1000$\,km\,s$^{-1}$ and
$i$ in the range 81\degr--85\degr, we get a smearing amplitude of $156
- 87$\,km\,s$^{-1}$, which is of the order of or below the resolution of our
map. Hence, our map of HU~Aqr \ is essentially blind to the vertical motions.

\begin{figure}[th]
\psfig{figure=curtain_ps,width=88mm,bbllx=27mm,bburx=195mm,bblly=126mm,bbury=236mm,clip=}
\caption[view_fwd]{\label{view_fwd}
Scheme of the accretion geometry in HU~Aqr \ as seen by a hypothetical observer
located at the center of the white dwarf.
Matter leaves the secondary star
at the $L_1-$point and follows a ballistic trajectory, hence it is deflected
under the influence of Coriolis forces to the left. The stream leaves the
orbital plane and couples onto field lines at an azimuth of 43\degr, where the
absorption dip occurs. Three field lines
connecting the stagnation region and the white dwarf are shown indicating
the width of the absorption dip (dark dotted region).
One additional trajectory (dashed line) is shown leaving the plane at the
$L_1-$point.
The region between this line
and the dense vertical stream is less dense dotted (accretion curtain).
}
\end{figure}

In Figs.~\ref{stream_geo} and \ref{view_fwd} the distribution of matter
in the system is shown. The dark shaded region in both figures are the
horizontal and vertical streams, while the dotted region gives a schematic
of the accretion curtain necessary for shielding the leading hemisphere.
This curtain is constrained by a trajectory which couples to the magnetic field
at the $L_1$-point. This gives not the required 60\% derived above
obscuration indicating
that the view taken here is still too simplistic. Additional obscuration
will be provided by nature by the finite width of the stream at the $L_1$
which is of the order of 10\% of the secondary star's radius.

We can use our stream models to obtain estimates for physical
parameters of the stagnation region. The extent of this region in the
orbital plane (length along the trajectory) is $l \simeq 6 \times 10^9$\,cm and
along which the undisturbed dipole field strength varies between 3 and 9 kG.
The polar field strength
was set to $B = 38$\,MG which yields a field strength in the accretion spot
of about 36-37\,MG as required by the identification of cyclotron harmonics
(Schwope et al.~1993, Glenn et al.~1994). Our code assumes a constant cross
section along the trajectory, $\rho v = \dot{m} = \rm{constant}$. Coupling at
different loci along the trajectory is possible by a variation of the
density $\rho$, thus varying the ram pressure $p_{\rm ram} \propto \rho v^2$
of the stream. Under these assumptions we found that the
ratio of the ram and magnetic pressure varies by a factor of 6--7 along the
trajectory in the stagnation region.
The size of the stagnation region
is transferred down to the white dwarf surface via dipole field lines where
it occupies a region with full opening angle of about 5\degr --6\degr
corresponding to a linear dimension of $l \simeq 7 \times 10^7$\,cm
for a white dwarf with radius $R_{\rm wd} = 7 \times 10^8$\,cm.

The tomogram together with the schemes of the accretion geometry
also yields hints for an understanding of the lightcurves of the
HVC and the BBC (Fig.~\ref{lc_3comp}). Both components are brighter during
first half of the orbital cycle, when we view the magnetic curtain's
concave illuminated side.
The HVC is bright and easily to recognize in the trailed spectrogram
around quadrature phases. The observed spectra at these phases correspond
to projections of the map parallel to the $v_x-$axis, hence along the
cometary tail, producing a sharp feature in a spectrogram.
The observed spectra at conjunction phases, on the other hand, correspond
to projections along the $v_y-$axis. At these phases emission from the
horizontal stream is smeared over an interval of $\sim$1000\,km\,s$^{-1}$ \
which produces only very broad spectral features. Hence, at theses phases
the HVC apparently vanishes and we obtain the minima in the lightcurve
of the HVC.

\section{Discussion and conclusions}

We have found two distinct features in the trailed spectrograms of the four
main emission lines in the blue spectral regime of HU~Aqr, in particular the
line of ionized Helium He\,{\sc ii}\,$\lambda$4686, which are potentially useful
for a determination of the stellar masses. These are the amplitude of the
radial velocity curve of the narrow emission line NEL and the location and
curvature of the
horizontal stream in the tomogram, the Doppler image of the HVC.
An additional constraint on the
mass ratio is set by the observed eclipse length. All these constraints are
shown in a $(Q, i)-$plane in Fig.~\ref{qi_rel} with $Q$ being the mass ratio
and $i$ the orbital inclination. The eclipse length is dependent
on the size of the secondary star's Roche lobe and the inclination, hence
relation (1) in the diagram is purely geometrical (it is of course implicitly
assumed that the secondary fills exactly its Roche lobe) (Chanan et
al.~1976). The solid line is valid for the measured eclipse length,
the nearby dashed line is valid for the maximum correction
which accounts for the offset of the accretion spot from the white dwarfs
center, see above. Relation (2)
in the diagram for the NEL makes use of a factor
which relates the center of light of the illuminated hemisphere to the
center of mass. This factor is dependent on $Q$ and shown in Horne \& Schneider
(1989) for the optically thin and in Schwope et al.~(1993) for the
optically thick models. The differences between both modes are negligible as
far as this factor is concerned.
The computation of the curves (2) in the $(Q,i)-$plane makes use further
of the
Roche geometry (approximation of the spherical equivalent Roche-radius
as a function of $Q$ given by Eggleton (1983)) and Kepler's third law.
We have assumed that the secondary is a main sequence star and
can be described by a ZAMS mass-radius relation for late-type stars.
With  $M_2 = 0.146$\,M$_\odot$, the
empirical relation by Caillault \& Patterson (1990) predicts the least
compact secondary for HU~Aqr, the other extreme with $M_2 = 0.206$\,M$_\odot$
is due to the relation by VandenBerg et al.~(1983) (solid and dashed lines in
Fig.~\ref{qi_rel}).
Relation (3) finally is the result
of a fit-per-eye to the location and curvature of the horizontal
stream in the tomogram which relies on the
assumption that the center of light along the ridge of He\,{\sc ii}\,$\lambda$4686 \
marks the single-particle trajectory. This results in the smallest estimates
of $Q$ with $Q \simeq 2.5$.

\begin{figure}[t]
\psfig{figure=qi_rel_ps,width=88mm,bbllx=8mm,bburx=200mm,bblly=53mm,bbury=245mm,clip=}
\caption[qi_rel]{\label{qi_rel}
Mass determination of HU~Aqr \ using the observed length of the eclipse (1), the
radial velocity amplitude of the illuminated hemisphere of the secondary
star with different mass-radius relations (2), and the curvature of the
ballistic stream in the Doppler map (3).
}
\end{figure}

It is clear from Fig.~\ref{qi_rel} (as well as from several previous
Figures) that no unique solution exists presently in the framework of the
models presented here.
Relations (1) and (2) suggest high values of the mass ratio and the
inclination with $Q \simeq 4.5 - 5.5, i > 85\degr$ for the Helium lines
and $Q = 5 - 5.5, i > 87\degr$ for the
Balmer lines (the latter are not shown in Fig.~\ref{qi_rel}).
The curvature of the stream of He\,{\sc ii}\,$\lambda$4686, He\,{\sc i}\,$\lambda$4471\ and H$\beta$ on the other
hand suggests, that the mass ratio might be as low as $Q = 2.5$ and that
the inclination correspondingly might be as low as $i \simeq 80\degr$.
Both estimates of the mass ratio seem to exclude each other presently and
it appears likely that neither the NEL (in combination with $K_2$-correction
and ZAMS-approximation) nor the HVC (fitted by a single-particle trajectory)
can be used straightly to give an accurate mass estimate.

The disagreement between both approaches becomes smaller if one assumes that
NEL emission is more concentrated towards
the center of mass of the secondary than we have assumed. An absorbing cloud
of matter in the $L_1$-region which would suppress emission from the `nose'
of the secondary could e.g.~provide the necessary bias of the effective radial
velocity amplitude towards higher values (and could also lower the width of
the line profiles, Fig.~\ref{fwhm_nel}).
The expected re-emission might be responsible for the longish
extension of the bright spot near the $L_1$-point in the tomogram of H$\beta$.
That such bias exists appears likely from the observed higher NEL-velocity
of the Hydrogen Balmer lines with respect to the Helium lines. The `nose'
is more effectively shielded in the more optically thick Hydrogen lines.

The best way to solve the conflict and to calibrate the
M/R-relation of the secondary star would be
to measure the radial velocity of the secondary star independently using
e.g.~photospheric absorption lines. This will help to sort out which
feature (NEL, HVC) of which line may serve as {\it the} estimator of the
mass ratio.
It requires HU~Aqr\ to be observed
in a low state of accretion. Such a measurement is highly demanded in order to
calibrate either of the methods used here for mass determination.
Another hint to the likely mass of the stars and the mass ratio could be
derived from ingress/egress length into/from eclipse of the white dwarf
itself, rather than ingress/egress of the accretion spot on it.

Our model with $Q = 2.5$ implies that the secondary star
in HU~Aqr\ must be as massive as 0.35\,M$_\odot$. It would be much
more compact than a ZAMS-star and in consequence much more
luminous. This would imply that the distance estimates given by
Glenn et al.~(1994) and Schwope et al.~(1993) are lower limits only.

\medskip
We have presented high-resolution spectral observations of the eclipsing
AM Herculis star HU~Aqr\ obtained when the system was in a high state of
accretion. We have identified three emission line components in our
trailed spectra of He\,{\sc ii}\,$\lambda$4686, He\,{\sc i}\,$\lambda$4471, and the H-Balmer lines. These could be
uniquely identified as originating on the illuminated hemisphere of the
secondary star (the narrow emission line NEL), the stream in the orbital
plane (the high-velocity component HVC) following a ballistic trajectory,
and the stream coupled onto field lines out of the orbital plane
(the broad-base component BBC). We have uniquely identified
the horizontal stream in this AM Her-binary by means of Doppler tomography
and could trace it from the $L_1$-point down to the stagnation region.
On the assumption that the
NEL of He\,{\sc ii}\,$\lambda$4686 is formed on the surface of the Roche-lobe of the companion
star we have determined its mass. This estimate is in disagreement with an
estimate derived from the tomogram. We propose that Doppler tomography
of the ballistic stream can be used as a new tool for the mass determination
of accreting binaries provided we can calibrate this method using an
independent mass determination.

\acknowledgements
We thank M.~Giampapa for helpful comments concerning chromospheric emission
from late-type stars and H.~Ritter for useful hints concerning their
mass-radius relation. We thank an anonymous referee for helpful comments.
This work was supported in part by the Deutsche Forschungsgemeinschaft
under grant Schw 536/4-1 and the BMFT under grant 50 OR 9403 5.

redpajama_set_name: RedPajamaArXiv


text:
Chance meetings can lead to incredible results: for the two core members of Thus Owls, it has led not only to love, but also to almost a decade's worth of music-making.
Comprised of husband and wife Erika and Simon Angell, Thus Owls have been performing since 2007 – initially as a quartet fronted by the Swedish-bred Erika before she had met Simon, who had been working as a guitarist for Patrick Watson and would eventually join the group after meeting Erika in Amsterdam while both were touring Europe – and have released three full-length LPs; the last of which was 2014's Turning Rocks, which was long-listed for that year's Polaris Music Prize.
This Thursday, the duo will be at the Gésu playing a show for Montréal en Lumière, which the duo are treating like a release show of sorts for their new EP Black Matter, released in November on Secret City Records. Both this show and their show in Toronto four days earlier will be their last for a while, as they are expecting their first child in early March.
"It's the first big show we've done in a while in our hometown," says Erika. "It's also the first time that we're able to play the music from that EP with strings and backup singers and everything that was arranged for the music, so it's super exciting for us."
Black Matter itself is a six-song mixture of very experimental, sometimes ominous-sounding indie pop with a visible influence of electronic music, with a heavy emphasis on synths this time around. Written largely over the course of two weeks while the duo had a residency in New York, influence for the EP came partially through experimental artists like Ben Frost and Daniel Bjarnason – the latter of whom collaborated on the EP – as well as shows and museums they went to during their stay. Musically, the EP came partially through the two wanting to get out the more avant-garde side of the music they've been listening to, in addition to being a sort of "offspring" of their previous bodies of work.
"There was a longing and a need enough to do something in a different kind of musical lane that is also who we are, but that we haven't maybe expressed through Thus Owls before," she says. "We just wanted to create a little collaborative album – ourselves and a few musicians that we really enjoy and we like to work with: Liam O'Neill from Suuns and Daniel Bjarnason from Iceland who worked on our string arrangements. It was so much fun; it was very spontaneous and super important for us, but a very natural process."
The inspiration for certain songs also came through unconventional circumstances – for example, the title track was borne in part from an iPhone-recorded drum riff sent from drummer Stefan Schneider to Erika and Simon, which the two then wrote music over. Regardless of how each song came together, it's an effort that may have been created with a more relaxed attitude this time around.
"I think [with] an EP, you don't have the same heavy image of a whole record in front of you," she adds. "When you create it, it's more just for the fun of it or the inspiration. It's different mentally somehow, and the whole process of it was very easy. It's different than Thus Owls might have sounded before, but at the same time, it's very much our songwriting that shines through."
In terms of what Black Matter means to her from a personal standpoint, Erika says it's a bit like a wrap-up of the experience she had moving to Canada from Sweden, and "coming out on the other side" after overcoming the phase of adapting to a new country and environment.
"It's a little bit like starting high school, coming to a new country like 'who am I here? Who will be?', feeling insecure and all that," she says. "I felt that I set my feet down properly around the time when these lyrics came together, and that I could be all of me here."
Dave MacIntyre Blog at WordPress.com.

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text:
Home Science Reports Reports and News Life Sciences
Systems Biology of Antibiotics
Bacteria can quickly become resistant to antibiotics. Which mechanisms are responsible for this and how to counteract it? Dr. Ana Rita Brochado, who is setting up a new Emmy Noether Junior Research Group at the University of Würzburg, is investigating this.
Bacteria have fascinating properties. They adapt excellently to their respective environment, and they existed long before humans. Their toughness has led to the fact that bacteria have successfully spread all over the world for three billion years – even in places where humans could not survive, for example in the hottest springs and in the coldest places on earth.
Dr. Ana Rita Brochado investigates the effect of antibiotics on bacteria.
Bild: Jörg Fuchs / Universität Würzburg
However, they were only discovered a few hundred years ago. Since that time, research has been examining these tiny creatures more and more closely.
Biotechnology engineer Dr. Ana Rita Brochado has also taken a liking to microbes. She has been setting up an Emmy Noether Junior Research Group at the Biocenter of Julius-Maximilians-Universität Würzburg (JMU) in Bavaria, Germany, since early 2019. Her topic: "Systems Biology of Antibiotics in Gram-negatives."
»Biocenter »Biotechnology »DFG »EMBL »Escherichia coli »antibiotic »bacteria
Dr. Brochado is funded by the JMU Biocenter Nachwuchsprogramm, by the ZINF Young Investigator program and by the German Research Foundation (DFG). The Emmy Noether Programme by DFG offers outstanding young researchers the opportunity to lead junior research groups on their own responsibility and thus qualify for a professorship. The DFG will provide Brochado with up to 1,82 million euros for her group.
Gram-negative bacteria at a glance
Dr. Brochado is interested in bacterial pathogens. "Bacteria are very small but extremely tough creatures. They use complex mechanisms to cope with their environmental conditions," said the researcher. This can lead to problems if they infect humans. "Mutations can quickly make bacteria resistant to antibiotics that will no longer work," she explains. "The weapons with which medicine fights bacterial infections quickly become dull. New strategies are permanently in demand."
Her research focuses particularly on gram-negative bacteria. These are infectious agents which are particularly difficult to treat, due to the complex structure of their cellular envelope: in addition to the cell wall, they have an external biomembrane that makes them very resistant to external compounds, such as antibiotics.
Reviving old antibiotics with vanilla against pathogens
Ana Rita Brochado and her group are investigating the molecular mechanisms underlying antibiotic activity using a systems biology approach. "It is not the case that bacteria simply die when they come into contact with an antibiotic," she explains, "in this process numerous mechanisms are set in motion. We will use different compounds alone and in combination to better understand the complexity of the bacterial response to these compounds."
Among other things, the scientist showed that different bacteria react in a very specific manner to antibiotic combinations, and also that food compounds can be used to enhance the activity of antibiotics against resistant bacteria. For instance, particular clinical isolates of Escherichia coli which are resistant to the antibiotic spectinomycin could be successfully combated by combining the antibiotic with the aroma substance vanillin (Brochado et al., Nature, 2018). Vanillin is the major component of vanilla flavor.
Career of the junior research group leader
Ana Rita Brochado has completed several research stations in Europe. She obtained her Master's degree in Biotechnology Engineering in her native Portugal at the Instituto Superior Técnico in Lisbon. She received her PhD from the Technical University of Denmark in Lyngby in 2012 with a thesis modelling of yeast metabolism.
She then moved to Germany, where she did postdoctoral research at the group of Dr. Athanasios Typas at the European Molecular Biology Laboratory (EMBL) in Heidelberg until the end of 2018. During her postdoc, she became interested in antibiotic action and developed high-throughput approaches to study antibiotic combinations in bacteria.
Ana Rita Brochado moved from EMBL to JMU Würzburg at the beginning of 2019. Here she is setting up her Emmy Noether Junior Research Group at the Chair of Microbiology at the Biocenter. She does not only want to cooperate with Professor Thomas Rudel, who holds the chair, but also with other groups: "I am particularly interested in quantitative biology and biology of infection. Thanks to its well-connected research landscape, JMU offers me the best conditions to carry out combined basic research in these fields."
But that's not all. "Of course, we want to make our findings useful for patient care," said Brochado. "To do this, many research teams have to work together to successfully transfer research results from the laboratory into clinical studies. I see excellent opportunities for this in Würzburg."
Long research tradition in Würzburg
She is not alone with this assessment. Würzburg has a long and successful tradition in the research of bacteria. As early as 1880, the physician Theodor Escherich discovered a bacterium in the human intestine in Würzburg that was named after him – Escherichia coli.
Even today, Würzburg is an outstanding supra-regional location for bacterial research. Founded in 1993, the ZINF Research Center for Infectious Diseases of JMU – which Ana Rita Brochado is also a member as a Young Investigator – is the oldest university institution in Germany dedicated to the interdisciplinary and cross-faculty research of infectious diseases. The Helmholtz Institute for RNA-based Infection Research, founded in 2017, is also of particular importance. The subsidiary institute of the Braunschweig Helmholtz Centre – Germany's largest institution for infection research – works and conducts research within the framework of a strategic partnership with the JMU.
Dr. Ana Rita Brochado, Chair of Microbiology, Biocenter, University of Würzburg, T +49 931 31-88860, anarita.brochado@uni-wuerzburg.de
https://www.biozentrum.uni-wuerzburg.de/mikrobio/mitarbeiter/dr-ana-rita-brochad... Website Dr. Brochado
https://www.eurekalert.org/pub_releases/2018-07/embl-cac070218.php "Combining antibiotics changes their effectiveness": EMBL press release about the publication in Nature
Robert Emmerich | Julius-Maximilians-Universität Würzburg
Further reports about: > Biocenter > Biotechnology > DFG > EMBL > Escherichia coli > antibiotic > bacteria
More articles from Life Sciences:
15.07.2019 | Max Planck Institute of Immunobiology and Epigenetics
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text:
Q: Microdata Markup - 'Brand > Logo' with Icon Font for Logo
The above class='logo' applies a font to the icon element. Can we apply the 'glyph' defined in the class (e.g.,  font-family: 'AnyFont'; content: '/e600') as a Microdata Markup DataType "Brand > Logo" to render the Logo in a rich-snippet the same as a image would render in the rich-snippet?
This doesn't seem likely as an image has a URL based src="..." property and a font character does not, none the less I've been researching this I've found no documentation or discussion on this and need to know if the community is aware of a way to make this work if it does't already work. Or do we have to forfeit the many well-known benefits of using an icon-font to display a logo in rich-snippets?
As validation to the common application of microdata to an image and not an font-character we see that this heavily used microdata generator doesn't give us an option to apply microdata to an element with a font applied to it. And based on the 'Brand > Logo' documentation, the only options are ImageObject and URL (which many very well may believe this answers the question (there's bound to be a way to do this without having to go back 4 years and use an image instead of a font)).

A: You could use a link element (which may be used in the body in HTML5+Microdata) to provide the URL of the logo:

  <link itemprop="logo" href="logo.png" />

(I used span instead of i. And for the record, I don't agree that it's a good idea to include a site's logo via CSS instead of HTML.)

redpajama_set_name: RedPajamaStackExchange


text:
Q: I have added Splash screen plugin but splash screen not working in cordova visual studio 2015 I added this in config.xml file. is it any Remaining to add?
`<preference name="SplashScreen" value="screen" />
<preference name="SplashScreenDelay" value="10000" />

<platform name="android">
    <splash src="res/screens/android/320X470.jpg" density="land-hdpi" />
    <splash src="res/screens/android/320X470.jpg" density="land-ldpi" />
    <splash src="res/screens/android/320X470.jpg" density="land-mdpi" />
    <splash src="res/screens/android/320X470.jpg" density="land-xhdpi" />
    <splash src="res/screens/android/320X470.jpg" density="port-hdpi" />
    <splash src="res/screens/android/320X470.jpg" density="port-ldpi" />
    <splash src="res/screens/android/320X470.jpg" density="port-mdpi" />
    <splash src="res/screens/android/320X470.jpg" density="port-xhdpi" />
  </platform>

 <vs:plugin name="cordova-plugin-splashscreen" version="3.0.0" />`

A: I had the same problem. In my case the splash screen was not displayed long enough (although "SplashScreenDelay" was set). The reason for that was the following line in the app.Ready event:
navigator.splashscreen.hide();

I removed that line and the splash screen worked as expected.


text:
Home Features Favorite Rides Favorite Ride: Unexpected Serenity in Southern California
Favorite Ride: Unexpected Serenity in Southern California
Andrew Thweatt
There's 2,000 feet to climb back up from the desert floor on the wonderfully twisty and smooth Banner Grade. (Photos by the author)
Is there any scenic countryside left for motorcyclists in the urban sprawl of Southern California? Actually there is, and it's surprisingly close to the densely populated areas of San Diego County and amazingly diverse in climate, altitude and scenery.
Starting off early on a weekday from my house in Escondido, 30 miles north of San Diego, it's a quick jump onto County Road S6 (Valley Center Road) and past the rural town of Valley Center, and then the Rincon Indian Reservation. It's immediately after Rincon that the ride starts in earnest. A right turn onto State Route 76 takes me directly into long sweepers sculpted perfectly into sloped citrus groves, as I begin climbing the foothills guarding the southern flank of Palomar Mountain. The road steepens suddenly as it leaves the groves, runs through a few tight switchbacks and then empties out on top of a ridge. An immediate left takes me back onto S6, also known as South Grade Road here, and then a steep climb up Palomar. Oak trees give way to pines as I twist left and right through as technical a ride as you will find in Southern California. The dense pine forest lining the pavement acts as an echo chamber and reflects back the dull roar of my Kawasaki ZRX1200 accelerating out of each turn. The road is nearly an elevator, taking me through 21 switchbacks up to the 5,200-foot summit—a 2,500-foot climb in less than seven miles. The view from the top is stunning. On a clear morning like this, you can easily see west to the Pacific Ocean and south to the Mexican border.
Carrying passengers and mail from St. Louis to San Francisco, the Butterfield Stage Line passed through this area of rural Southern California two times each week from 1857 to 1861.
The temperature is pleasantly cool, and nearly 20 degrees lower than back in suburbia. I take off southeast at the summit junction down the East Grade Road (County Road S7), a much more gradual decent, with gentler curves but a rougher road surface that demands concentration. A deer crosses abruptly in front of me a few minutes down the road, a reminder that I'm nowhere near the city now. Soon enough, I catch a glimpse of Lake Henshaw off to the east, signaling the end of the grade and my reunion with the smooth and fast Route 76. Lake-effect fog briefly engulfs me and dampens my face shield as I roll through gentle curves and glide past the lake, emerging back into bright sunshine at the intersection with State Route 79.
A landmark since the 1930s, the Julian Drug Store sports an old-time soda fountain and candy mine.
A quick left and I roll out into decidedly more open country, with brown grass fields and scattered small groves of oaks, reminiscent of the rolling hill country of the California Central Coast. Another right turn onto San Felipe Road (County Road S2), and I begin a gentle climb through rolling hills of cow country dotted with an occasional flock of wild turkeys. A crest over Teofulio Summit at 3,700 feet, and the scenery (and temperature) begins changing rapidly and dramatically. Within seven more miles of the wide, sweeping curves of S2, I spot the first cactus, and I'm opening all the vents on my jacket as the temperature climbs back up to 90 degrees. To my right, the green coastal mountains rise abruptly up to more than 5,000 feet, and to my left are the brown and barren desert hills framing the Anza-Borrego Desert State Park. A stark contrast indeed.
Only 45 minutes from the summit of Palomar Mountain, and the scene has changed from pines to cacti as you skirt the border of the Anza-Borrego Desert State Park.
As I intersect the dry beginnings of San Felipe Wash, the highway tees into State Route 78 at Scissors Crossing, and a hot, dry wind suddenly picks up, indicative of the sudden temperature and pressure changes between the coast and desert. A left turn would drop me immediately into the desert proper, but a right turn instead takes me past an old Butterfield Stage Route stop and, within just a few more miles, the Kawasaki and I are gaining altitude again, assaulting the eastern slope of the San Diego coastal range. Similar to my earlier climb up Palomar, but with fresher asphalt and smoother corners most of the way, Banner Grade, as it's known to locals, writhes its way tightly up the mountain. It climbs nearly 2,000 feet back into the pines and cool temperatures, and empties out at the summit into the quaint little mountain town of Julian. Famous for its apple pies and cider, Julian is a busy tourist attraction even on a mid-week morning, so after a brief stop to stretch my legs, I take a left at the only stop sign, continuing on down through a bending, gradual decent to the old mission settlement of Santa Ysabel. Known to the savvy traveler as the home of Dudley's Bakery, the beautiful Santa Ysabel tempts me to halt my brisk pace and make time for a dash into Dudley's for a cheese Danish and cup of their exceptional coffee, which I do.
Don't look down! It's a nearly 2,500-foot drop from the summit of South Grade Road to the valley below.
Then it's off for the home stretch of the ride. The temperature warms again as I ride through undulating hills and moderate curves in grassy countryside. Old wooden barns, horses and even a buffalo or two on the Star B Ranch make the landscape strangely Wyoming-like at times. Twenty more minutes of beautiful scenery brings me to Ramona, a horse-and-cow rural town full of character, and the last stop before descending a long grade down to the orange groves and dairy farms of the San Pasqual Valley and then back into Escondido. The coastal humidity hits me in full force now, a massive contrast to the dry wind just an hour back at Scissors Crossing. A few more traffic lights and a sprint down the carpool lane on Interstate 15, and I'm at the office by 9:00 a.m.
Four distinct climates in less than three hours, and other than a mild case of helmet hair, no one's the wiser.
You can't say they didn't warn you. There is some serious climbing and twisting ahead to reach the Palomar Mountain summit.
A clear day on the mountain. The marine fog layer from the Pacific encompasses the valley to the west and the hills of Mexico can be seen to the south.
Map of the route taken, by Bill Tipton/compartmaps.com
California Motorcycle Rides
Great Roads West
bob miller January 5, 2017 At 1:17 pm
Please pass this along to Clement Salvadori as this is more of a qustion for him based on his long exprience with motorcycles rather thsn a comment, i recently had an automobile accident and while recovering well I am starting to have some concens about riding my goldwing due to the size and weight. I wanted to ask Clement for a recommendation on a smaller bike still suitable for two up riding and touring.
jsmith January 5, 2017 At 3:08 pm
Thanks for your question. We're guessing you might be a Honda guy since you have a Goldwing, so we'd recommend looking at the CTX1300 as your next bike. At 734 pounds (claimed), it's 100 pounds lighter than the F6B and almost 200 pounds lighter than a Goldwing. We reviewed it back in 2014, and you can read it here: http://ridermagazine.com/2014/05/09/2014-honda-ctx1300-deluxe-road-test/.
We hope that helps!
Andrew Thweatt - January 23, 2023


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» Appealing a child support order
Appealing a child support order
On Behalf of Lenington, Gratton, & Associates LLP | May 19, 2021 | Family Law & Divorce |
If you currently owe child support, or you are in the midst of a divorce and you worry about your ability to make payments in the future, it is vital to explore various issues related to this facet of family law.
Sometimes, non-custodial parties can modify their child support order because of job loss or other major financial changes, making payments more tolerable. Furthermore, some people have the ability to appeal a child support order, but there are certain restrictions in place.
How can you appeal a child support order?
According to the Pennsylvania Child Support Program's website, those who wish to appeal a child support order can do so as long as they file the appeal in no more than 20 days following the order's date or the date they received the order.
If you appeal a child support order, you need to file your appeal in the Domestic Relations Section for the county in which the order originated. Moreover, you should note that filing an appeal is the only way to change a child support order.
What if a parent cannot appeal a child support order?
If more than 20 days have passed since the issuance of your child support order and you have lost the ability to file an appeal, review other courses of action if you wish to make changes regarding child support. For example, some parents can modify, reinstate or terminate child support orders. Falling behind on child support payments carries harsh repercussions and if you are a non-custodial parent with child support obligations, you should familiarize yourself with your options.
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Three reasons why a suit to quiet title may be necessary
Preparing to tell your children about divorce
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Bristol City and Nottingham Forest amongst a host of clubs interested in former-Middlesbrough defender
By Oliver Dixon on Jun 19, 2019 0 Comments
According to an exclusive report from TEAMtalk, Forest Green Rovers defender Nathan McGinley is attracting several Championship sides.
The report states that Bristol City, Huddersfield Town, Nottingham Forest and Swansea City are the four second tier sides keen on bringing McGinley back to the Championship.
The defender was previously on the books at Middlesbrough, although he only made one appearance for his hometown club in his four years on Teesside. McGinley's only game for Boro came earlier this season, as he played the full 90 minutes at left back in the Carabao Cup win over Notts County.
IN OTHER NEWS: Birmingham City sign ex-Arsenal midfielder- Fans reaction
After impressing on loan at Forest Green at the start of last season, his move was made permanent in January 2019, joining for an undisclosed fee.
He played 38 games in League Two last season for Rovers, helping them to achieve a fifth placed finish in just their second year in the Football League. Having made the League Two Play Off Semi Finals, they lost out on a trip to the final at Wembley, after being defeated over two legs against eventual Play Off winners Tranmere Rovers.
McGinley is a versatile defender, and has played at right back, left back and even centre back in his short career as a professional footballer. He is still only 22 years old and if he was to move to a Championship side in the near future, they would be ultimately be paying for potential.
IN OTHER NEWS: Luton Town hoping to complete deal for Croatia international goalkeeper
The report states that Forest Green Rovers manager Mark Cooper is bracing himself for offers for the youngster.
Oliver Dixon
Lifelong Boro fan - from the highs of watching Juninho and the Carling Cup victory, to the lows of Gordon Strachan and Lee Dong Gook
Cardiff tease Bristol City fans after former-defender Aden Flint signs from Middlesbrough
Former Birmingham City, Sheffield Wednesday and Charlton Athletic defender signs for Reading
Former Leeds defender says Newcastle goalkeeper could have blown his chances of a move
NEW IN THE CHAMPIONSHIP
NEW IN LEAGUE ONE
Coventry City to step up Nottingham Forest hotshot chase as Chaplin departs for Barnsley
Blackburn Rovers, Cardiff City and Charlton Athletic keen on midfielder after Aston Villa release
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Credit card processing online or card-not-present (keyed) merchants must take more precautions than merchants that process credit cards face-to-face, since they do not have the luxury of seeing the actual card or cardholder.
International shipping address -International banks (except Canada & UK) do not support address verification (AVS), so you need to be extra careful when shipping worldwide. Having the cardholder fax or email you a copy of their ID & credit card (front & back) is a good way to verify you are working with the real cardholder.
Multiple orders placed on the same card in a short time period – someone could be attempting to "charge a card" until the account is shut down or overdrawn.
Big ticket items – items that are easy to resell for big profits.
First time shopper – scammers are always looking for new sites that are "card able" and don't take fraud seriously.
Multiple orders for a single IP address – If someone is placing multiple orders using multiple cards from the same IP address this should throw up a big flag.
"Next day" shipping or "Rush" orders – Thieves want your product ASAP so they can accept delivery and resale before the fraudulent transaction is noticed or reported.
Orders from customers that use free email services – Since these services involve no billing, the user has not been verified and cannot be tracked.
Transactions placed on multiple cards but shipped to the same address – possible sign of a batch of stolen cards being used or account numbers being generated by a software program.
Always obtain an authorization code.
Verify additional information on the card such as the expiration date, Card Verification Value 2 (CVV2), and address verification service (AVS). If the cardholder is unable to provide this additional information or it does not match up, it may mean they do not actually have the card on their person.
Look for general warning signs (listed above).
If you suspect fraud (but still obtained an authorization code), ask for additional information (the name of the financial institution that issued the card), contact the cardholder directly, confirm the order by sending a note to the customers billing address first (if shipping address is different), and have the cardholder fax or email you a copy of their ID & credit card.
Address Verification Service (AVS) -Most software & terminals support AVS on all "keyed" transactions. AVS verifies that the street number and zip code being used as the billing address matches up with the actual address on the cardholder's credit card billing statement.
Card Verification Value 2 (CVV2) – 3 digit number found on the back right side of all Visa, MasterCard, and Discover cards used as an additional way to verify that the customer placing the order has the card in hand. On American Express the CVV2 code is 4 digits and is located on the front top right of the card.