30 research outputs found
2MASSJ22560844+5954299: the newly discovered cataclysmic star with the deepest eclipse
Context: The SW Sex stars are assumed to represent a distinguished stage in
CV evolution, making it especially important to study them. Aims: We discovered
a new cataclysmic star and carried out prolonged and precise photometric
observations, as well as medium-resolution spectral observations. Modelling
these data allowed us to determine the psysical parameters and to establish its
peculiarities. Results: The newly discovered vataclysmic variable
2MASSJ22560844+5954299 shows the deepest eclipse amongst the known nova-like
stars. It was reproduced by totally covering a very luminous accretion disk by
a red secondary component. The temperature distribution of the disk is flatter
than that of steady-state disk. The target is unusual with the combination of a
low mass ratio q~1.0 (considerably below the limit q=1.2 of stable mass
transfer of CVs) and an M-star secondary. The intensity of the observed three
emission lines, H_alpha, He 5875, and He 6678, sharply increases around phase
0.0, accompanied by a Doppler jump to the shorter wavelength. The absence of
eclipses of the emission lines and their single-peaked profiles means that they
originate mainly in a vertically extended hot-spot halo. The emission H_alpha
line reveals S-wave wavelength shifts with semi-amplitude of around 210 km/s
and phase lag of 0.03. Conclusions: The non-steady-state emission of the
luminous accretion disk of 2MASSJ22560844+5954299 was attributed to the low
viscosity of the disk matter caused by its unusually high temperature. The star
shows all spectral properties of an SW Sex variable apart from the 0.5 central
absorption.Comment: Accepted for publication in Astronomy & Astrophysics. 12 pages, 11
figures, 6 table
The structure of cool accretion disc in semidetached binaries
We present the results of qualitative consideration of possible changes
occurring during the transition from the hot accretion disc to the cool one. We
argue the possible existence of one more type of spiral density waves in the
inner part of the disc where gasdynamical perturbations are negligible. The
mechanism of formation of such a wave as well as its parameters are considered.
We also present the results of 3D gasdynamical simulation of cool accretion
discs. These results confirm the hypothesis of possible formation of the spiral
wave of a new, "precessional" type in the inner regions of the disc. Possible
observational manifestations of this wave are discussed.Comment: LaTeX, 16 pages, 8 figures, to be published in Astron. Z
A Multi-Wavelength, Multi-Epoch Study of the Soft X-Ray Transient Prototype, V616 Mon (A0620-00)
We have obtained optical and infrared photometry of the soft x-ray transient
prototype V616 Mon (A0620-00). From this photometry, we find a spectral type of
K4 for the secondary star in the system, which is consistent with spectroscopic
observations. We present J-, H-, and K-band light curves modeled with WD98 and
ELC. Combining detailed, independently run models for ellipsoidal variations
due to a spotted, non-spherical secondary star, and the observed ultraviolet to
infrared spectral energy distribution of the system, we show that the most
likely value for the orbital inclination is 40.75 +/- 3 deg. This inclination
angle implies a primary black hole mass of 11.0 +/- 1.9 solar masses.Comment: 29 pages (preprint format), including 7 figures and 4 tables,
accepted for publication in the Nov 2001 issue of A
Quasi-Periodic Occultation by a Precessing Accretion Disk and Other Variabilities of SMC X-1
We have investigated the variability of the binary X-ray pulsar, SMC X-1, in
data from several X-ray observatories. We confirm the ~60-day cyclic variation
of the X-ray flux in the long-term monitoring data from the RXTE and CGRO
observatories. X-ray light curves and spectra from the ROSAT, Ginga, and ASCA
observatories show that the uneclipsed flux varies by as much as a factor of
twenty between a high-flux state when 0.71 second pulses are present and a
low-flux state when pulses are absent. In contrast, during eclipses when the
X-rays consist of radiation scattered from circumsource matter, the fluxes and
spectra in the high and low states are approximately the same. These
observations prove that the low state of SMC X-1 is not caused by a reduction
in the intrinsic luminosity of the source, or a spectral redistribution
thereof, but rather by a quasi-periodic blockage of the line of sight, most
likely by a precessing tilted accretion disk. In each of two observations in
the midst of low states a brief increase in the X-ray flux and reappearance of
0.71 second pulses occurred near orbital phase 0.2. These brief increases
result from an opening of the line of sight to the pulsar that may be caused by
wobble in the precessing accretion disk. The records of spin up of the neutron
star and decay of the binary orbit are extended during 1991-1996 by
pulse-timing analysis of ROSAT, ASCA, and RXTE PCA data. The pulse profiles in
various energy ranges from 0.1 to >21 keV are well represented as a combination
of a pencil beam and a fan beam. Finally, there is a marked difference between
the power spectra of random fluctuations in the high-state data from the RXTE
PCA below and above 3.4 keV. Deviation from the fitted power law around 0.06 Hz
may be QPO.Comment: Accepted to ApJ. 33 pages including 11 figure
Optical spectroscopy of flares from the black hole X-ray transient A0620-00 in quiescence
We present a time-resolved spectrophotometric study of the optical
variability in the quiescent soft X-ray transient A0620-00. Superimposed on the
double-humped continuum lightcurve are the well known flare events which last
tens of minutes. Some of the flare events that appear in the continuum
lightcurve are also present in the emission line lightcurves. From the Balmer
line flux and variations, we find that the persistent emission is optically
thin. During the flare event at phase 1.15 the Balmer decrement dropped
suggesting either a significant increase in temperature or that the flares are
more optically thick than the continuum. The data suggests that there are two
HI emitting regions, the accretion disc and the accretion stream/disc region,
with different Balmer decrements. The orbital modulation of H with the
continuum suggests that the steeper decrement is most likely associated with
the stream/disc impact region. We construct Doppler images of the H and
H emission lines. Apart from showing enhanced blurred emission at the
region where the stream impacts the accretion disc, the maps also show
significant extended structure from the opposite side of the disc. The trailed
spectra show characteristic S-wave features that can be interpreted in the
context of an eccentric accretion disc (abridged).Comment: 13 pages, 10 Figures, accepted my MNRA