The accretion disk in the post period-minimum cataclysmic variable SDSS J080434.20 + 510349.2

Abstract

Aims. This study of SDSS J080434.20+510349.2 is primarily concerned with the double-hump shape in the light curve and its connection with the accretion disk in this bounce-back system. Methods. Time-resolved photometric and spectroscopic observations were obtained to analyze the behavior of the system between superoutbursts. A qualitative geometric model of a binary system containing a disk with two outer annuli spiral density waves was applied to explain the light curve and the Doppler tomography. Results. Observations were carried out during 2008−2009, after the object's magnitude decreased to V ∼ 17.7 ± 0.1 from the March 2006 eruption. The light curve clearly shows a sinusoid-like variability with a 0.07 mag amplitude and a 42.48 min periodicity, which is half of the orbital period of the system. In September 2010, the system underwent yet another superoutburst and returned to its quiescent level by the beginning of 2012. This light curve once again showed a double-hump-shape, but with a significantly smaller (∼0.01 mag) amplitude. Other types of variability like a "mini-outburst" or SDSS1238-like features were not detected. Doppler tomograms, obtained from spectroscopic data during the same period of time, show a large accretion disk with uneven brightness, implying the presence of spiral waves. Conclusions. We constructed a geometric model of a bounce-back system containing two spiral density waves in the outer annuli of the disk to reproduce the observed light curves. The Doppler tomograms and the double-hump-shape light curves in quiescence can be explained by a model system containing a massive ≥0.7 M white dwarf with a surface temperature of ∼12 000 K, a late-type brown dwarf, and an accretion disk with two outer annuli spirals. According to this model, the accretion disk should be large, extending to the 2:1 resonance radius, and cool (∼2500 K). The inner parts of the disk should be optically thin in the continuum or totally void.

Short Orbital Period Cataclysmic Variables

“…Neustroev et al (2016) proposed that the leading side bright spot is caused by irradiation of tidally thickened sectors of the outer disk. We note that the normal hot spot and the emission structure on the opposite side of the disk can possibly explain double-humped light curves observed in WZ Sge-type stars [43,53].…”

“…Direct (spectral) evidence for brown-dwarf secondaries exists only for very few CVs (SDSS J143317.78+101123.3 and WZ Sge [39,40]), whereas the recognition of other candidates is based on radial velocity studies and analysis of the spectral energy distribution. Using such indirect methods, solid evidence for very low mass donor stars was found for GD 552 [41], EZ Lyn [42], V406 Vir [43], SSS J122221.7−311525 [37].…”

“…The contribution of disks to the continuum in WZ Sgetype and bounce-back systems is much less and does not exceed ∼40-50 per cent in the optical range [43]. Various authors support an idea that the inner parts of the disk need to be cleared up during quiescence.…”

“…Some form them are: the origin of long periods no related with orbital periods in FS Aur, GW Lib and V455 And (see [54] and references therein); a source of unexplained quasi-periodic mini-outbursts in EZ Lyn [42] and V406 Vir [43]; the relatively short time (4 years) between superoutbursts in WZ-type system V406 Vir [43]; unusual long lasting super-outburst in WZ-Sge-type system SSS J122221.7-311523 [37].…”

Long-term photometry of the eclipsing dwarf nova V893 Scorpii

“…While there may be mechanisms which lead to a period increase over the scale of the observational time base this is contrary to the expected secular period evolution of cataclysmic variables unless V893 Sco is a period bouncer. This, however, is rather unlikely since it does not exhibit any behaviour considered characteristic for CVs which have evolved beyond the period minimum (Zharikov et al 2013) such as broad Balmer line absorption troughs (see spectra shown by Mason et al 2001) or persistent orbital double humps in the light curve. Moreover, V893 Sco exhibits rather frequent (normal) dwarf nova outbursts, in contrast to the rare (WZ Sge type) superoutbursts expected for period bouncers.…”