Global Analysis of Mass Transfer Cycles in Cataclysmic Variables

We give a global analysis of mass transfer variations in CVs. We show that limit cycles driven by variations of the secondary star's radius alone require this radius to be sensitive to the instantaneous mass transfer rate. The only promising mechanism for this is irradiation of the secondary by the accreting primary. Explicit modelling of this process shows however that cycles do not occur for secondary masses < 0:65M. For such masses, the thermal inertia of the convective envelope is so large that irradiation cannot expand it relative to the Roche lobe, and the system nds a stable mass transfer rate. In constrast large{amplitude limit cycles occur for all secondary masses if the angular momentum losses from the binary are assumed to increase rather modestly with the mass transfer rate simultaneously with the radius variations.