MHD models of accretion/ejection phenomena in young stellar objects.

Abstract

   Nowadays there is a general consensus on the fact that accretion and ejection phenomena in Young Stellar Objects are strongly related and most likely driven by magnetohydrodynamic (MHD) processes. In particular organized large-scale magnetic fields can be responsible for the launching and collimation of jets and outflows. Despite a general agreement on the physics of the acceleration process, it is still debated whether the launching region is situated in the circumstellar accretion disk, on the surface of the rotating protostar, or in the region of interaction between the stellar magnetosphere and the disk. In this talk I will briefly review MHD numerical models of extended disk-winds, stellar winds and magnetospheric ejections. I will elucidate the physical conditions required to launch the different types of outflows. I will describe the dynamical characteristics of these ejection phenomena and their impact on the evolution of the stellar and disk angular momentum. Finally, I will try to test the different models against some observational constraint.