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