Time-dependent accretion onto magnetized white dwarfs

Abstract

Time-dependent accretion onto magnetized white dwarfs is considered. A detailed description of a numerical method of solution to the hydrodynamical equations is given. The postshock flow is cooled by optically thin bremsstrahlung and is thermally unstable. As a result the shock height undergoes periodic oscillations. The properties of this oscillation are considered as a function of the accretion rate and of the mass and radius of the white dwarf. The structure of the accretion flow depends on a single scaling parameter. Below a critical accretion rate, which depends on the particular white dwarf, the nature of the accretion flow changes and the shock propagates up the accretion column indefinitely.