120 research outputs found
X-ray observations of VY Scl type nova-like binaries in the high and low state
Four VY Scl-type nova-like systems were observed in X-rays during both the
low and the high optical states. We examined Chandra, ROSAT, Swift and Suzaku
archival observations of BZ Cam, MV Lyr, TT Ari, and V794 Aql. The X-ray flux
of BZ Cam is higher during the low state, but there is no supersoft X-ray
source (SSS) as hypothesized in previous articles. No SSS was detected in the
low state of the any of the other systems, with the X-ray flux decreasing by a
factor between 2 and 50. The best fit to the Swift X-ray spectra is obtained
with a multi-component model of plasma in collisional ionization equilibrium.
The high state high resolution spectra of TT Ari taken with Chandra ACIS-S and
the HETG gratings show a rich emission line spectrum, with prominent lines of
in Mg, Si, Ne, and S. The complexity of this spectrum seems to have origin in
more than one region, or more than one single physical mechanism. While several
emission lines are consistent with a cooling flow in an accretion stream, there
is at least an additional component. We discuss the origin of this component,
which is probably arising in a wind from the system. We also examine the
possibility that the VY Scl systems may be intermediate polars, and that while
the boundary layer of the accretion disk emits only in the extreme ultraviolet,
part of the X-ray flux may be due to magnetically driven accretion.Comment: 13 pages, 8 figures, 7 tables. Accepted for publication by MNRA
Photometric and Spectroscopic Investigation of the Dwarf Nova HS 0218+3229: A Short Review
This paper is devoted to the study of the cataclysmic variable HS 0218+3229 using the photometric and spectroscopic observations
Optical studies of the X-ray transient XTE J2123-058 -I. Photometry
We present optical photometry of the X-ray transient XTE J2123-058, obtained
in July-October 1998. The light curves are strongly modulated on the 5.95hrs
orbital period, and exhibit dramatic changes in amplitude and form during the
decline. We used synthetic models which include the effect of partial eclipses
and X-ray heating effects, to estimate the system parameters, and we constrain
the binary inclination to be i=73+-4 degrees. The model is successful in
reproducing the light curves at different stages of the decay by requiring the
accretion disc to become smaller and thinner by 30% as the system fades by 1.7
mags in the optical. From Aug 26 the system reaches quiescence with a mean
magnitude of R=21.7+-0.1 and our data are consistent with the optical
variability being dominated by the companion's ellipsoidal modulation.Comment: 6 pages, 6 figure
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