Long-term evolution of a dipole type magnetosphere interacting with an accretion disk. II. Transition into a quasi-stationary spherically radial outflow

Abstract

The evolution of an initially stellar dipole type magnetosphere interacting with an accretion disk is investigated numerically using the ideal MHD ZEUS-3D code in the 2D-axisymmetry option. The simulations last several thousands of Keplerian periods of the inner disk. A Keplerian disk is assumed as a boundary condition prescribing a mass inflow into the corona. Additionally, a stellar wind from a rotating central star is prescribed. Our major result is that the initially dipole type field develops into a spherically radial outflow pattern with two main components, a disk wind and a stellar wind component. These components evolve into a quasi- stationary final state. The poloidal field lines follow a conical distribution. As a consequence of the initial dipole, the field direction in the stellar wind is opposite to that in the disk wind. The maximum speed of the outflow is about the Keplerian speed at the inner disk radius. With the chosen mass flow rates and field strength we see almost no indication for a flow self-collimation.