The evolutionary thermal response of a white dwarf to compressional heating by periodic dwarf nova accretion events
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Abstract
The thermal response of the underlying white dwarf in a cataclysmic variable to the periodic deposition of mass by a dwarf nova accretion event is simulated with a quasi-static stellar evolution code incorporating time variable accretion. After accretion at rates typical of dwarf nova outbursts (approx. 10-7 to 10-8/yr) for outburst durations of days to 2 weeks, the radial infall is shut off and the evolution of the white dwarf is followed during dwarf nova quiescence. The matter is assumed to accrete softly with the same entropy as the white dwarf outer layers. In some sequences accretion is resumed and shut off repeatedly at intervals of months to simulate the thermal evolution of the white dwarf in typical dwarf novae such as SS Cygni and U Geminorum, between successive dwarf nova outbursts. Thermal timescales for white dwarf cooling following a given dwarf nova outburst depend upon the accretion rate, outburst duration, and white dwarf mass; they are nominally in the range 0.2-0.8 years for parameters typical of dwarf novae (white dwarf masses in the range 1.2-0.6 solar mass, outburst accretion rates in the range 1 x 10-7-10-8 solar mass/yr, outburst durations in the range 7-14, days and quiescent intervals of 30-300 days). If the e-folding timescale of the white dwarf cooling is shorter than the quiescent interval bewteen outbursts, then the effect of compressional heating is too small to be observationally detectable.
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