http://arxiv.org/abs/1908.10867
In our earlier Paper I, we showed that the accretion disc radius of the dwarf nova HT Cas in its quiescent state has not changed significantly during many years of observations, remaining consistently large, close to the tidal truncation radius. This result is not consistent with the modern understanding of the evolution of the disc radius through an outburst cycle. Spectroscopic observations of HT Cas during its superoutburst offered us an exceptional opportunity to compare the properties of the disc of this object in superoutburst and in quiescence. We obtained a new set of time-resolved spectra of HT Cas in the middle of its 2017 superoutburst. We used Doppler tomography to map emission structures in the system, which we compared with those detected during the quiescent state. The superoutburst spectrum is similar in appearance to the quiescent spectra, although the strength of most of the emission lines decreased. Most of the line profiles are complex with a mix of absorption and emission components. H$\alpha$ in superoutburst was much narrower than in quiescence, whereas the profiles of other Balmer and HeI lines did not change significantly. Doppler maps of the Balmer and He I lines are dominated by a bright emission arc in the right side of the tomograms, superposed on a diffuse ring of emission. The location of the leading arc on the H$\beta$, He I, and Si II maps is consistent with Keplerian velocities at the tidal truncation radius. However, the bulk of the H$\alpha$ emission has significantly lower velocities. We show that the accretion disc radius of HT Cas during its superoutburst has remained the same size as it was in quiescence. Instead, we detected cool gas beyond the accretor’s Roche-lobe, possibly expelled from the hot disc during the superoutburst.
V. Neustroev and S. Zharikov
Fri, 30 Aug 19
44/58
Comments: 10 pages, 8 figures, 2 tables. Submitted to A&A. This is the second paper of a series of two. The first paper can be found here arXiv:1506.04753
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