MAGNETIC RECONNECTION IN A MAGNETOSPHERE-ACCRETION-DISK SYSTEM - AXISYMMETRICAL STATIONARY STATES AND 2-DIMENSIONAL RECONNECTION SIMULATIONS

In the present paper we investigate the transport of accreting plasma across the magnetopause onto a strongly magnetized massive star (i.e. white dwarf or neutron star) by magnetic reconnection. A simplified ax isymmetric magnetic field model of an aligned rotator is used to study the reconnection process. To be able to separate effects caused by in stabilities of the system from intrinsic time-dependent behaviour, we first construct self-consistent stationary states of the magnetosphere -disk system. We include a rigid magnetospheric rotation and Keplerian rotation of the magnetized disk plasma. The stationary states are com puted numerically with a relaxation method which conserves the magneti c topology. Therefore we can prescribe an initial condition of the rel axation process using a magnetic field consisting of a dipole of the c ompact object and a homogeneous field threading the disk. The magnetop ause then separates the regions of closed field lines with corotating plasma from open field lines with plasma in Keplerian motion. The resi stive stability of the stationary states is examined by two-dimensiona l magnetohydrodynamic simulations. We find that magnetic reconnection leads to mass transport across the magnetopause onto closed magnetic f ield lines The accretion disk material is accelerated along the magnet ic field lines that are connected to the magnetic poles of the compact object and will eventually be accreted by the star at its polar caps.