paper

Winds from accretion disks driven by the radiation and magnetocentrifugal force

arXiv:astro-ph/0002441 · doi:10.1086/309154

Abstract

We study the 2-D, time-dependent hydrodynamics of radiation-driven winds from luminous accretion disks threaded by a strong, large-scale, ordered magnetic field. The radiation force is due to spectral lines and is calculated using a generalized multidimensional formulation of the Sobolev approximation. The effects of the magnetic field are approximated by adding a force that emulates a magnetocentrifugal force. Our approach allows us to calculate disk winds when the magnetic field controls the flow geometry, forces the flow to corotate with the disk, or both. In particular, we calculate models where the lines of the poloidal component of the field are straight and inclined to the disk at a fixed angle. Our numerical calculations show that flows which corotate with the disk have a larger mass loss rate than their counterparts which conserve specific angular momentum. The difference in the mass loss rate between these two types of winds can be several orders of magnitude for low disk luminosities but vanishes for high disk luminosities. Winds which corotate with the disk have much higher velocities than angular momentum conserving winds. Fixing the wind geometry stabilizes winds which are unsteady when the geometry is derived self-consistently. The inclination angle between the poloidal velocity and the normal to the disk midplane is important. Non-zero inclination angles allow the magnetocentrifugal force to increase the mass loss rate for low luminosities, and increase the wind velocity for all luminosities. Our calculations also show that the radiation force can launch winds from magnetized disks. The line force can be essential in producing MHD winds from disks where the thermal energy is too low to launch winds or where the field lines make an angle of < 30^o with respect to the normal to the disk.

arXiv commentLaTeX, 11 pages, 6 color postscript or PJEG files, to appear in ApJ

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