163 research outputs found
Swift Observations of Shock Evolution in RS Ophiuchi
Our \textit{Swift} observations of RS Oph form an unprecedented X-ray dataset
to undertake investigations of both the central source and the interaction of
the outburst ejecta with the circumstellar environment. Over the first month,
the XRT data are dominated by emission from rapidly evolving shocks. We discuss
the differences in derived parameters from those found for \textit{RXTE} at
early times and the evolution of the X-ray emission to much later times. It is
apparent that at late times several emission components are present. We find no
strong evidence of the proposed shock break-out in our data.Comment: 5 pages, 3 figures, to appear in ASP conference proceedings Volume
401 "RS Ophiuchi (2006) and the recurrent nova phenomenon
Chandra detection of extended X-ray emission from the recurrent nova RS Ophiuchi
Radio, infrared, and optical observations of the 2006 eruption of the
symbiotic recurrent nova RS Ophiuchi (RS Oph) showed that the explosion
produced non-spherical ejecta. Some of this ejected material was in the form of
bipolar jets to the east and west of the central source. Here we describe Xray
observations taken with the Chandra X-ray Observatory one and a half years
after the beginning of the outburst that reveal narrow, extended structure with
a position angle of approximately 300 degrees (east of north). Although the
orientation of the extended feature in the X-ray image is consistent with the
readout direction of the CCD detector, extensive testing suggests that the
feature is not an artifact. Assuming it is not an instrumental effect, the
extended X-ray structure shows hot plasma stretching more than 1,900 AU from
the central binary (taking a distance of 1.6 kpc). The X-ray emission is
elongated in the northwest direction - in line with the extended infrared
emission and some minor features in the published radio image. It is less
consistent with the orientation of the radio jets and the main bipolar optical
structure. Most of the photons in the extended X-ray structure have energies of
less than 0.8 keV. If the extended X-ray feature was produced when the nova
explosion occurred, then its 1".2 length as of 2007 August implies that it
expanded at an average rate of more than 2 mas/d, which corresponds to a flow
speed of greater than 6,000 km/s (d/1.6 kpc) in the plane of the sky. This
expansion rate is similar to the earliest measured expansion rates for the
radio jets.Comment: accepted in Ap
Resonance line-profile calculations based on hydrodynamical models of cataclysmic variable winds
We present synthetic line profiles as predicted by the models of 2-D line-
driven disk winds due to Proga, Stone & Drew. We compare the model line
profiles with HST observations of the cataclysmic variable IX Vel. The model
wind consists of a slow outflow that is bounded on the polar side by a fast
stream. We find that these two components of the wind produce distinct spectral
features. The fast stream produces profiles which show features consistent with
observations. These include the appearance of the P-Cygni shape for a range of
inclinations, the location of the maximum depth of the absorption component at
velocities less than the terminal velocity, and the transition from absorption
to emission with increasing inclination. However the model profiles have too
little absorption or emission equivalent width. This quantitative difference
between our models and observations is not a surprise because the line-driven
wind models predict a mass loss rate that is lower than the rate required by
the observations. We note that the model profiles exhibit a double-humped
structure near the line center which is not echoed in observations. We identify
this structure with a non-negligible redshifted absorption which is formed in
the slow component of the wind where the rotational velocity dominates over
expansion velocity. We conclude that the next generation of disk wind models,
developed for application to CVs, needs to yield stronger wind driving out to
larger disk radii than do the present models.Comment: LaTeX, 19 pages, to appear in Ap
Dynamics of Line-Driven Winds from Disks in Cataclysmic Variables. I. Solution Topology and Wind Geometry
We analyze the dynamics of 2-D stationary, line-driven winds from accretion
disks in cataclysmic variable stars. The driving force is that of line
radiation pressure, in the formalism developed by Castor, Abbott & Klein for O
stars. Our main assumption is that wind helical streamlines lie on straight
cones. We find that the Euler equation for the disk wind has two eigenvalues,
the mass loss rate and the flow tilt angle with the disk. Both are calculated
self-consistently. The wind is characterized by two distinct regions, an outer
wind launched beyond four white dwarf radii from the rotation axis, and an
inner wind launched within this radius. The inner wind is very steep, up to 80
degrees with the disk plane, while the outer wind has a typical tilt of 60
degrees. In both cases the ray dispersion is small. We, therefore, confirm the
bi-conical geometry of disk winds as suggested by observations and kinematical
modeling. The wind collimation angle appears to be robust and depends only on
the disk temperature stratification. The flow critical points lie high above
the disk for the inner wind, but close to the disk photosphere for the outer
wind. Comparison with existing kinematical and dynamical models is provided.
Mass loss rates from the disk as well as wind velocity laws are discussed in a
subsequent paper.Comment: 21 pages, 10 Postscript figures; available also from
http://www.pa.uky.edu/~shlosman/publ.html. Astrophysical Journal, submitte
Identification of selected sources from the ROSAT Galactic Plane Survey - I
We report on optical searches in the error circles of 93 ROSAT survey sources
located at low galactic latitudes (|b| < 20 deg). These sources were extracted
from the ROSAT Galactic Plane Survey using various selection criteria on
hardness ratio, X-ray and optical brightness and integrated galactic absorption
in the direction of the source. We find optical identifications in 76 cases,
among which are 25 new AGN, 6 new CVs and a new Be/X-ray binary. In order to
illustrate the relevance of the source selections applied here, we
cross-correlated the ROSAT all-sky survey bright source list with SIMBAD.
Different classes of X-ray emitters populate distinct regions of a multi
dimensional parameter space involving flux ratios, galactic latitude and Nh.
This relatively good segregation offers the possibility to build source samples
with enhanced probability of identification with a given class. Complete
optical identification of such subsamples could eventually be used to compute
meaningful probabilities of identification for all sources using as basis a
restricted set of multi-wavelength information.Comment: 18 pages, 7 figures, Postscript. Optical spectra and finding charts
available at ftp://cdsarc.u-strasbg.fr/pub/xray/rgps_idI.ps.gz Submitted to
Astronomy & Astrophysics, Supplement Serie
Infall variability in the Classical T Tauri system VZ Chamaeleonis
We present time series spectroscopy of the Classical T Tauri star VZ Cha. We
follow spectral variations at intermediate resolution over five successive
nights, or approximately two rotation periods. We see profile features which
persist on timescales longer than the expected infall time from the inner disc,
and we see expected evidence of rotational variations in the lines, but we also
note that rotation alone cannot produce all the observed variability and some
other mechanism must be invoked. The behaviour of H-alpha is observed to be
markedly different from that of the other lines. In particular, the evidence of
rotational effects is lacking at H-alpha, and the activity in the red and blue
wings of the line is not significantly correlated, in contrast to the other
Balmer lines.Comment: 10 pages, includes 14 postscript file
Rotation of Jets from Young Stars: New Clues from the Hubble Space Telescope Imaging Spectrograph
We report findings from the first set of data in a current survey to
establish conclusively whether jets from young stars rotate. We observed the
bi-polar jets from the T Tauri stars TH28 and RW Aur, and the blue-shifted jet
from T Tauri star LkH321, using the Hubble Space Telescope Imaging
Spectrograph (HST/STIS). Forbidden emission lines (FELs) show distinct and
systematic velocity asymmetries of 10 -- 25 (+/- 5) km/s at a distance of 0".3
from the source, representing a (projected) distance of ~ 40 AU along the jet
in the case of RW Aur, ~ 50 AU for TH28, and 165 AU in the case of
LkH321. These velocity asymmetries are interpreted as rotation in the
initial portion of the jet where it is accelerated and collimated. For the
bi-polar jets, both lobes appear to rotate in the same direction. Values
obtained were in agreement with the predictions of MHD disk-wind models
(Bacciotti et al 2002, Anderson et al 2003, Dougados et al 2003, Pesenti et al
2003). Finally, we determine, from derived toroidal and poloidal velocities,
values for the distance from the central axis of the footpoint for the jet's
low velocity component of ~ 0.5 - 2 AU, consistent with the models of
magneto-centrifugal launching (Anderson et al 2003).Comment: 17 pages, 10 figures, Accepted by Ap
Astrophysical Fluids of Novae: High Resolution Pre-decay X-ray spectrum of V4743 Sagittarii
Eight X-ray observations of V4743 Sgr (2002), observed with Chandra and
XMM-Newton are presented. The nova turned off some time between days 301.9 and
371, and the X-ray flux subsequently decreased from day 301.9 to 526 following
an exponential decline time scale of days. We use the absorption
lines present in the SSS spectrum for diagnostic purposes, and characterize the
physics and the dynamics of the expanding atmosphere during the explosion of
the nova. The information extracted from this first stage is then used as input
for computing full photoionization models of the ejecta in V4743 Sgr. The SSS
spectrum is modeled with a simple black-body and multiplicative Gaussian lines,
which provides us of a general kinematical picture of the system, before it
decays to its faint phase (Ness et al. 2003). In the grating spectra taken
between days 180.4 and 370, we can resolve the line profiles of absorption
lines arising from H-like and He-like C, N, and O, including transitions
involving higher principal quantum numbers. Except for a few interstellar
lines, all lines are significantly blue-shifted, yielding velocities between
1000 and 6000 km/s which implies an ongoing mass loss. It is shown that
significant expansion and mass loss occur during this phase of the explosion,
at a rate . Our measurements show that the efficiency of the amount of
energy used for the motion of the ejecta, defined as the ratio between the
kinetic luminosity and the radiated luminosity , is
of the order of one.Comment: 25 pages, 9 figures. Accepted in book: Recent Advances in Fluid
Dynamics with Environmental Applications, pp.365-39
Spitzer and ground-based infrared observations of the 2006 eruption of RS Ophiuchi
We present Spitzer Space Telescope and complementary ground-based infrared
observations of the recurrent nova RS Ophiuchi, obtained over the period 64-111
days after the 2006 eruption. The Spitzer IRS data show a rich emission line
spectrum superimposed on a free-free continuum. The presence of fine structure
and coronal infrared lines lead us to deduce that there are at least two
temperatures (1.5e5K and 9e5K) in the ejecta/wind environment, and that the
electron density in the `cooler' region is 2.2e5 cm-3. The determination of
elemental abundances is not straightforward but on the assumption that the Ne
and O fine structure lines arise in the same volume of the ejecta, the O/Ne
ratio is >~0.6 by number.Comment: 13 pages, 4 figures, accepted for publication in ApJ Letter
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