Torques and instabilities in intermediate polars

The observed spin periods of the primaries in intermediate polars require the presence of torques additional to the standard expectation of material and magnetic torques from an accretion disc. In an extension of earlier work by Wickramasinghe, Wu and Ferrario, from rates of mass transfer deduced from optical and X-ray fluxes, and assuming surface magnetic fields similar to those observed in the most rapidly rotating low mass main sequence stars, it is shown that the magnetohydrodynamic torque between the partially shielded primary and the secondary is sufficient to account for the observed spin periods. It is further found that there is a range of magnetic moments and mass transfer rates in which synchronized rotation of the primary can occur even though it possesses an accretion disc. This may account for the structures deduced for V795 Her and V2051 Oph. An analysis of the observed outbursts (or lack of) in the intermediate polars shows that whereas many systems are explainable in terms of the standard theory of ct-discs, in some systems the magnetic structure is supressing expected outbursts and instabilities that are as yet not understood appear in their place.