A model for WZ Sge with "standard" values of alpha

Abstract

We present a model for the dwarf nova WZ Sge which does not require assuming unusually and unexplained low values of the viscosity alpha-parameter during exceptionally long quiescent states of this system. We propose that the inner parts of the accretion disc are disrupted by either a magnetic field or evaporation, so that the disc is stable (or very close to being stable) in quiescence, as the mass transfer rate is very low and the disc can sit on the cool, lower branch of the thermal equilibrium curve. Outbursts are triggered by an enhanced mass transfer, which brings the disc into the unstable regime of the standard dwarf nova disc instability model. The resulting eruptions are strongly affected by the irradiation of the secondary star. Our model reproduces very well the recurrence time and the characteristics of the light curve in outburst.