Magnetized accreting stars: Studies of the inner accretion disk edge by a magnetohydrodynamical approach. I. Construction and analysis of magnetopause equilibria

In this paper a numerical model of the interaction between the accretion di sk and the magnetosphere of an accreting object (e.g., a neutron star) is u sed to study mechanisms that can lead to fast accretion of matter due to ma gnetic forces. The framework of magnetohydrodynamics (MHD) provides a simpl e but powerful tool for such a study on a semiglobal scale. The aim of this work is the construction of stationary states that describe the inner-edge region of the accretion disk with the star's rotating magnetosphere suppor ting the inner disk edge against gravitation. The equilibrium magnetic fiel ds are computed numerically by a finite difference scheme using the magneto friction method within ideal magnetohydrodynamics. To study the mass loadin g onto the magnetosphere we vary disk mass density and pressure. Magnetosph ere rotation speed and magnetopause thickness are additonal variables contr ibuting to the shape of the magnetosphere and the currents in the magnetopa use at the disk edge.