SDSS J080434.20+510349.2: Cataclysmic Variable Witnessing the   Instability Strip?
  SDSS J080434.20+510349.2 is the 13th dwarf nova containing a pulsating white dwarf. Among the accreting pulsators that have experienced a dwarf novae outburst, SDSS J0804 has the most dramatic history of events within a short time scale: the 2006 outburst with 11 rebrightenings, series of December 2006 - January 2007 mini-outbursts, the 2010 outburst with 6 rebrightenings. Over 2006-2011, SDSS J080434.20+510349.2 in addition to positive 0.060^d superhumps during the outburst and 1-month post-outburst stage, 0.059005^d orbital humps in quiescence, displayed a significant short-term variations with periods P1 = 12.6 min, P2 = 21.7 min, P3 = 14.1 min and P4 = 4.28 min. The 12.6-min periodicity first appeared 7 months after the 2006 outburst and was the most prominent one during the following \sim 900 days. It was identified as non-radial pulsations of the white dwarf. The period of this pulsations varied within a range of 36 s, and amplitude changed from 0.013m to 0.03m. Simultaneously one could observe the 21.7-min and 14.3-min periodicities with a much lower significance level. During the minioutbursts the 21.7-min periodicity became the most powerful, the 12.6-min periodicity was less powerful, and the 12.6-min periodicity had the lowest significance. After the 2011 outburst the most prominent short-term periodicity appeared \sim 7 months after the outburst, but at 4.28 min. We identified that variability with periods P2, P3 and P4 could be additional pulsation modes, however the relation of P4 to white dwarf pulsation also can't be excluded. 
E. Pavlenko, V. Malanushenko, G. Tovmassian, S. Zharikov, T. Kato, N.   Katysheva, M. Andreev, A. Baklanov, K. Antonyuk, N. ...
astro-ph.SR