On the boundary layer of accretion discs

Stationary models for accretion disc-boundary layer systems based on the sl im disc approximation with radial radiative and advective energy transport included are constructed. Arguing that application of even the modified cau sal alpha-prescription in the boundary layer is questionable, we resort to the classical form of Prandtl's mixing length theory for a parametrization of the viscosity. It is shown that the coupling between pressure and viscos ity inherent in the alpha-prescription is responsible for characteristic fe atures of the boundary layer solutions in the standard approach. This coupl ing is relaxed when using the viscosity proposed in this paper. Then the bo undary layer structure becomes significantly different from standard soluti ons, and major drawbacks of the alpha-model, such as the coexistence of hig h viscosity and rigid rotation, do not occur. The properties of the new bou ndary layer-disc solutions are demonstrated by application to non-magnetic cataclysmic variables.