Voracious vortexes in cataclysmic variables. A multi-epoch tomographic study of HT Cassiopeia

We present multi-epoch, time-resolved optical spectroscopic observations of the dwarf nova HT Cas, obtained during 1986, 1992, 1995 and 2005 with the aim to study the properties of emission structures in the system. We determined that the accretion disc radius, measured from the double-peaked emission line profiles, is persistently large and lies within the range of 0.45-0.52a, where a is the binary separation. This is close to the tidal truncation radius r_max=0.52a. This result contradicts with previous radius measurements. An extensive set of Doppler maps has revealed a very complex emission structure of the accretion disc. Apart from a ring of disc emission, the tomograms display at least three areas of enhanced emission: the hot spot from the area of interaction between the gas stream and the disc, which is superposed on the elongated spiral structure, and the extended bright region on the leading side of the disc, opposite to the location of the hot spot. The position of the hot spot in all the emission lines is consistent with the trajectory of the gas stream. However, the peaks of emission are located in the range of distances 0.22-0.30a, which are much closer to the white dwarf than the disc edge. This suggests that the outer disc regions have a very low density, allowing the gas stream to flow almost freely before it starts to be seen as an emission source. We have found that the extended emission region in the leading side of the disc is always observed at the very edge of the large disc. Observations of other cataclysmic variables, which show a similar emission structure in their tomograms, confirm this conclusion. We propose that the leading side bright region is caused by irradiation of tidally thickened sectors of the outer disc by the white dwarf and/or hot inner disc regions.Comment: 15 pages, 12 figures. Minor modifications to match version published by Astronomy & Astrophysic

Time resolved spectroscopy and photometry of the dwarf nova FS Aurigae in quiescence

We present results of non-simultaneous time resolved photometric and spectroscopic observations of little-studied dwarf nova FS Aur in quiescence. The spectrum of FS Aur shows strong and broad emission lines of hydrogen and HeI, and of weaker HeII 4686 and CIII/NIII blend, similar to other quiescent dwarf novae. All emission lines are single-peaked, however their form varies with an orbital phase. Absorption lines from a late-type secondary are not detected. From the radial velocity measurements of the hydrogen lines H_beta and H_gamma we determined a most probable orbital period P=0.059+-0.002 d. This period agrees well with the 0.0595+-0.0001 estimate by TPST. On the other hand, the period of photometric modulations is longer than spectroscopic period and can be appreciated at least as 3 hours. Longer time-scale coverage during a single night is needed to resolve this problem. Using semi-amplitude of the radial velocities, obtained from measurements of hydrogen and helium lines, and some empirical and theoretical relations we limited basic parameters of the system: a mass ratio q>=0.22, a primary mass M_1=0.34 \div 0.46 M_sun, a secondary mass M_2<=0.1M_sun, and an inclination angle i=51^{\circ }-65^{\circ}. Doppler tomography have shown at least two bright region in accretion disk of FS Aur. The first more bright spot is located at phase about 0.6. The second spot is located opposite to the first one and occupies an extensive area at phases about 0.85-1.15

Dark spot, Spiral waves and the SW Sex behaviour: it is all about UX Ursae Majoris

We present an analysis of time-resolved, medium resolution optical spectroscopic observations of UX UMa in the blue (3920-5250 A) and red (6100-7200 A) wavelength ranges, that were obtained in April 1999 and March 2008 respectively. The observed characteristics of our spectra indicate that UX UMa has been in different states during those observations. The blue spectra are very complex. They are dominated by strong and broad single-peaked emission lines of hydrogen. The high-excitation lines of HeII 4686 and the Bowen blend are quite strong as well. All the lines consist of a mixture of absorption and emission components. Using Doppler tomography we have identified four distinct components of the system: the accretion disc, the secondary star, the bright spot from the gas stream/disc impact region, and the unique compact area of absorption in the accretion disc seen as a dark spot in the lower-left quadrant of the tomograms. In the red wavelength range, both the hydrogen (H_alpha) and neutral helium (HeI 6678 and HeI 7065) lines were observed in emission and both exhibited double-peaked profiles. Doppler tomography of these lines reveals spiral structure in the accretion disc, but in contrast to the blue wavelength range, there is no evidence for either the dark spot or the gas stream/disc impact region emission, while the emission from the secondary star is weak. During the observations in 1999, UX UMa showed many of the defining properties of the SW Sex stars. However, all these features almost completely disappeared in 2008. We have also estimated the radial velocity semi-amplitudes K_1 and K_2 and evaluated the system parameters of UX UMa. These estimates are inconsistent with previous values derived by means of analysis of WD eclipse features in the light curve in the different wavelength ranges.Comment: 16 pages, 9 figures, Accepted for publication by MNRA

The origin of seed photons for Comptonization in the black hole binary Swift J1753.5-0127

Aims. The black hole binary SWIFT J1753.5-0127 is providing a unique data set to study accretion flows. Various investigations of this system and of other black holes have not, however, led to an agreement on the accretion flow geometry or on the seed photon source for Comptonization during different stages of X-ray outbursts. We place constraints on these accretion flow properties by studying long-term spectral variations of this source. Methods. We performed phenomenological and self-consistent broad band spectral modeling of Swift J1753.5-0127 using quasi-simultaneous archived data from INTEGRAL/ISGRI, Swift/UVOT/XRT/BAT, RXTE/PCA/HEXTE and MAXI/GSC instruments. Results. We identify a critical flux limit, F \sim 1.5 \times 10^{-8} erg/cm^2/s, and show that the spectral properties of SWIFT J1753.5-0127 are markedly different above and below this value. Above the limit, during the outburst peak, the hot medium seems to intercept roughly 50 percent of the disk emission. Below it, in the outburst tail, the contribution of the disk photons reduces significantly and the entire spectrum from the optical to X-rays can be produced by a synchrotron-self-Compton mechanism. The long-term variations in the hard X-ray spectra are caused by erratic changes of the electron temperatures in the hot medium. Thermal Comptonization models indicate unreasonably low hot medium optical depths during the short incursions into the soft state after 2010, suggesting that non-thermal electrons produce the Comptonized tail in this state. The soft X-ray excess, likely produced by the accretion disk, shows peculiarly stable temperatures for over an order of magnitude changes in flux. Conclusions. The long-term spectral trends of SWIFT J1753.5-0127 are likely set by variations of the truncation radius and a formation of a hot, quasi-spherical inner flow in the vicinity of the black hole. (abridged)Comment: 16 pages, 8 figures, published in A&