Abstract:
The primary white dwarf of the cataclysmic variable SDSS J074531.92+453829.6 was discovered to exhibit nonradial
pulsations in 2006 January. This accreting white dwarf underwent its first recorded dwarf nova outburst
in 2006 October, during which its brightness increased by more than 5 mag. A Hubble Space Telescope (HST)
ultraviolet spectrum, obtained one year after the outburst, revealed a white dwarf temperature of 16,500 K, hotter
than all other known accreting white dwarf pulsators. This implies that the accreting primary white dwarf of
SDSS J074531.92+453829.6 was heated to temperatures beyond the instability strip during the outburst. Optical
observations acquired a year after the outburst did not reveal any evidence of pulsations, suggesting that the white
dwarf had not cooled to quiescence by then. We recently acquired optical high-speed time-series photometry on
this cataclysmic variable SDSS J074531.92+453829.6 more than three years after its outburst to find that pulsations
have now returned to the primary white dwarf. Moreover, the observed pulsation periods agree with pre-outburst
periods within the uncertainties of a few seconds. This discovery is significant because it indicates that the outburst
did not affect the interior stellar structure, which governs the observed pulsation frequencies. It also suggests
that the surface of the white dwarf has now cooled to quiescence. Using this discovery in addition to the prior
HST temperature measurement of 16,500 K, we have been able to constrain the matter accreted during the 2006
outburst. This is the first time an accreting white dwarf was unambiguously observed to resume pulsating after
an outburst.
