Modeling Accretional Heating in Dwarf Novae

Abstract

We present a grid of evolutionary models of white dwarfs in cataclysmic variables undergoing accretional heating due to periodic dwarf nova events. Our quasi-static evolutionary sequences incorporate time-variable accretion, compressional heating, and boundary layer irradiation, including the effect of the stellar rotational velocity. The thermal evolution of a white dwarf is followed over many dwarf nova accretion cycles. We assess the effect of accretional heating on the surface observables of the accreting white dwarf as a function of the accretor mass, initial surface temperature, and accretion rate. We compare our theoretical results with recent observations of two systems, both in decline from an outburst of 12 days duration: RX And and U Gem. In order for the theoretical results to fit the observations, we find that RX And must have a massive white dwarf accretor (≈1.2 M⊙). For U Gem the parameters of the white dwarf, particularly the white dwarf mass and temperature, are accurately known, and this leads to a mass accretion rate of 3.0 × 10-10 M⊙ yr-1 during the decline phase, i.e., 20 times smaller than its outburst value.