ENERGY-RELEASE IN STELLAR MAGNETOSPHERES

The interaction of a stellar magnetosphere with a thin accretion disk is considered. Specifically, I consider a model in which (1) the accre tion disk is magnetically linked to the star over a large range of rad ii and (2) the magnetic diffusivity of the disk is sufficiently small that there is little slippage of field lines within the disk on the ro tation time scale. In this case the magnetic energy built up as a resu lt of differential rotation between the star and the disk is released in quasi-periodic reconnection events occuring in the magnetosphere (A ly and Kuijpers 1990). The radial transport of magnetic flux in such a n accretion disk is considered. It is show that the magnetic flux dist ribution is stationary on the accretion time scale, provided the time average of the radial component of the field just above the disk vanis hes. A simple model of the time-dependent structure of the magnetosphe re is presented. It is shown that energy release in the magnetosphere must take place for (differential) rotation angles less than about 3 r adians. The magnetic flux distribution in the disk depends on the prec ise value of the rotation angle.