Hydrogen shell flashes in a white dwarf with mass accretion

Abstract

The evolution of a 0.8-solar-mass white dwarf accreting hydrogen-rich matter at various rates is followed through a number of hydrogen shell flashes in order to discover those properties of the evolutionary models which are independent of the initial conditions. The initial model has an isothermal degenerate hydrogen-exhausted core, a stationary hydrogen-burning shell source, and a static hydrogen-rich envelope. It is found that the flash strength generally decreases with increasing accretion rate, that the interflash period decreases very strongly with increasing accretion rate, and that the maximum surface luminosity for all flashes followed past maximum is essentially the luminosity given by the degenerate-core mass-luminosity relation for red giants (about 22,000 suns). The results also indicate that hydrogen shell burning is stable when the accretion rate is high and that models which undergo shell flashes exist in either a high or a low state. It is noted that the models considered are not relevant to novae or dwarf novae, but may explain the behavior of some symbiotic stars.