On the stability of magnetic wind-driven accretion discs

We consider the stability of winds that flow from accretion discs. We investigate the case that accretion in the disc arises from magnetic torques provided by the wind, while the mass outflow in the wind is centrifugally driven by magnetic torques provided by the disc. We derive a simplified model of the disc-wind magnetic interaction. In general, three possible equilibria can exist. The first solution corresponds to no mass accretion in the disc and no outflow in the wind. The second corresponds to a solution in which the wind removes disc angular momentum smoothly at all rad , with little wind mass outflow compared with disc inflow. The third corresponds to a very strong removal of disc angular momentum at some radius, with nearly all the disc mass locally lost to the wind. We argue that the first solution is stable, the second unstable, and the third is stable but may be unphysical.