Disc accretion onto white dwarfs

In non-magnetic cataclysmic variables (CVs) a white dwarf accretes matter from a main-sequence secondary star via an accretion disc. The dynamical behaviour of the accretion disc determines the accretion rate onto the white dwarf. Thermal instabilities in the accretion disc associated with the ionisation of hydrogen can lead to a limit-cycle behaviour in which the disc switches quasi-periodically between high and low accretion states. This thermal limit-cycle model is the generally accepted explanation for dwarf nova outbursts observed in many CVs. The process of disc accretion in non-magnetic CVs is subject to a number of external conditions, namely mass transfer variations of the secondary star, stream overflow and irradiation by the white dwarf. In this thesis I develop a model for time-dependent disc accretion onto white dwarfs and analyse the influence of these external conditions on the accretion process. I examine the effects of mass transfer variations by deriving real mass transfer variations from light curve monitoring of the disc-less CV AM Her. These mass transfer variations I include in simulations of disc accretion onto white dwarfs in non-magnetic systems and find that the mass accretion rate of the disc relaxes to an equilibrium with the prevailing mass transfer rate on a rather short timescale. I conclude that the observed changes in outburst duration and outburst magnitude are caused by nearly simultaneous variations of the mass loss rate from the secondary