Launching of jets and the vertical structure of accretion disks

The launching of magnetohydrodynamic outflows from accretion disks is consi dered. We formulate a model for the local vertical structure of a thin disk threaded by a poloidal magnetic field of dipolar symmetry. The model consi sts of an optically thick disk matched to an isothermal atmosphere. The dis k is supposed to be turbulent and possesses an effective viscosity and an e ffective magnetic diffusivity. In the atmosphere, if the magnetic field lin es are inclined sufficiently to the vertical, a magnetocentrifugal outflow is driven and passes through a slow magnetosonic point close to the surface . We determine how the rate of mass loss varies with the strength and incli nation of the magnetic held. In particular, we find that for disks in which the mean poloidal held is sufficiently strong to stabilize the disk agains t the magnetorotational instability, the mass-loss rate decreases extremely rapidly with increasing held strength and is maximal at an inclination ang le of 40 degrees -50 degrees. For turbulent disks with weaker mean fields, the mass-loss rate increases monotonically with increasing strength and inc lination of the field, but the solution branch terminates before achieving excessive mass-loss rates. Our results suggest that efficient jet launching occurs for a limited range of held strengths and a limited range of inclin ation angles in excess of 30 degrees. In addition, we determine the directi on and rate of radial migration of the poloidal magnetic flux and discuss w hether configurations suitable for jet launching can be maintained against dissipation.