DISK ACCRETION ONTO A MAGNETIZED YOUNG STAR AND ASSOCIATED JET FORMATION

We investigated disk accretion onto a magnetized young star by perform ing MHD numerical simulations. We considered the case in which the ste llar magnetosphere truncates the accretion disk carrying the interstel lar magnetic field, and the star is magnetized in the same direction a s the disk. In such a case, the interface between the accretion disk a nd the magnetosphere contains a magnetically neutral ring in the equat orial plane. The numerical results show that the disk accretion drives the magnetic reconnection between the magnetospheric field and the di sk magnetic field, which allows mass transfer from the disk to the mag netosphere. Most of the transferred mass accretes to the star along th e reconnected magnetospheric field, while the rest of the mass is acce lerated to the bipolar directions by a Lorentz force along the stellar open magnetic field. This ''reconnection-driven'' jet is further acce lerated magneto-centrifugally due to stellar rotation, and corresponds to optical jets from young stars. The magnetic braking as a reaction of the magneto-centrifugal acceleration of the jet may explain the obs erved slow rotations of young stars in the disk-accretion stage.