MHD simulations of the long-term evolution of a dipolar magnetosphere surrounded by an accretion disk

The evolution of an initially stellar dipole type magnetosphere interacting with an accretion disk is investigated using numerical ideal MHD simulations. The simulations follow several 1000 Keplerian periods of the inner disk. The initial dipole type magnetic field develops into a spherically radial outflow pattern with two main components both evolving into a quasi-stationary final state. A neutral field line divides both components, along which small plasmoids are ejected in irregular time intervals. The half opening angle of the stellar wind cone varies from 30 to 55 degrees depending on the ratio of the mass flow rates of disk wind and stellar wind. The maximum speed of the outflow is about the Keplerian speed at the inner disk radius. An axial jet forms during the first decades of rotation. However, this feature does not survive on the very long time scale and a pressure driven low velocity flow along the axis evolves.