Formation of magnetohydrodynamic jets: flares as triggers of internal shocks

We investigate how the overall jet formation process is affected by a variation in the accretion disk magnetic flux profile and/or the existence of a central stellar magnetosphere using axisymmetric magnetohydrodynamic (MHD) simulations. These simulations evolve from an initial, hydrostatic equilibrium state in a force-free magnetic field configuration. Two different simulation setups will be considered. In the first approach the role of the disk magnetic flux profile and disk mass loss profile is investigated concerning the jet collimation degree. Our results suggest (and quantify) that in general outflows launched from a very concentrated region close to the inner disk radius tend to be un-collimated. In the second approach, jet formation is numerically investigated from a magnetic field configuration consisting of a stellar dipole superposed by a disk field. The central dipole is found to de-collimate the disk wind considerably. Reconnecting flares are launched by the interaction of the disk and stellar magnetic field and may change the overall mass flux in the outflow by a factor of two. We apply the energetics and time scales of our numerical flare model to XRB sources