SDSS J080434.20+510349.2: Cataclysmic Variable Witnessing the Instability Strip?

Abstract

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 ∼ 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 0.013 m to 0.03 m . 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 ∼ 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.

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

“…This short recess between superoutbursts is atypical for WZ Sge-type systems. The amplitude of this superoutburst was similar to the previous, but the shape of the light curve was different: the brightness decreased faster and fewer echoes were detected (Pavlenko et al 2011). By December 2011, more than a year after this superoutburst, the brightness of the system fell practically to the quiescence level.…”

“…V455 And is a proven intermediate polar. In SDSS0804 a number of high-frequency periods were detected (Pavlenko et al 2011), but none was identified as a spin period so far. X-ray observations are needed to probe the magnetic properties of the white dwarfs in bounce-back candidates to verify the intermediate polar hypothesis.…”

“…In the three years after the 2006 superoutburst, the V-band magnitude of the object decreased to about 17.7 mag. However, the object never reached the pre-superoutburst level of March 2006 because in September 2010 SDSS0804 suddenly underwent another superoutburst (Pavlenko et al 2011), only ∼ 4.5 years after the previous one. This short recess between superoutbursts is atypical for WZ Sge-type systems.…”

“…About eight months after the first superoutburst, the brightness decreased to 17.1 magnitude. Variability at different timescales was detected: a rapid modulation with a period of P 1 = 12.6 min and amplitude of ∼ 0.05 mag was interpreted as a strong nonradial pulsation of the cooling (i.e., after the outburst) white dwarf, that entered the instability strip (Pavlenko et al 2006); significant short-term variations with periods P 2 = 21.7 min, P 3 = 14.1 min, and P 4 = 4.28 min that may be ad- ditional pulsation modes (Pavlenko et al 2011); and the superhumps were replaced with orbital double-hump-shape light variations (Zharikov et al 2008;Pavlenko et al 2007). In addition to these, the object also showed a new phenomenon -recurring (∼ 32 day) "mini-outbursts" that lasted approximately four days and increased the brightness to up to ∼ 0.6 mag (Zharikov et al 2008).…”

“…SDSS0804 exhibits some phenomena ("brightenings" and "mini-outbursts") that are not common in other CVs (Zharikov et al 2008). Its superoutburst in September 2010 (Pavlenko et al 2011), which was only about four years after the previous superoutburst, was unexpected. A general description of the characteristics and observational features of SDSS0804 can be found in Szkody et al (2006), Pavlenko et al (2007), Zharikov et al (2008), Kato et al (2009), and Pavlenko et al (2011).…”