Magnetocentrifugally Driven Winds: Comparison of MHD Simulations with Theory

Stationary magnetohydrodynamic (MHD) outflows from a rotating, conductingKeplerian accretion disk threaded by B-field are investigated numerically bytime-dependent, axisymmetric (2.5D) simulations using a Godunov-type code. Alarge class of stationary magneto-centrifugally driven winds are found wherematter is accelerated from a thermal speed at the disk to much larger velocity,greater than the fast magnetosonic speed and larger than the escape speed. Theflows are approximately spherical outflows with only small collimation withinthe simulation region. Numerical results are shown to coincide with thetheoretical predictions of ideal, axisymmetric MHD to high accuracy.Investigation of the influence of outer boundary conditions, particularly thaton the toroidal component of magnetic field shows that the commonly used``free'' boundary condition leads to artificial magnetic forces which can actto give spurious collimation. New boundary conditions are proposed which do notgenerate artificial forces. Artificial results may also arise for cases wherethe Mach cones on the outer boundaries are partially directed into thesimulation region.Comment: 19 pages, 18 figures, emulapj.sty is use