A WIND-DRIVEN WARPING INSTABILITY IN ACCRETION DISKS

ABSTRACT A wind passing over a surface may cause an instability in the surface, such as the Ñapping seen when wind blows across a Ñag or waves when wind blows across water. We show that when a radially outÑowing wind blows across a dense thin rotating disk, an initially Ñat disk is unstable to warping. When the wind is subsonic, the growth rate is dependent on the lift generated by the wind and the phase lag between the pressure perturbation and the vertical displacement in the disk caused by drag. When the wind is supersonic, the growth rate is primarily dependent on the form drag caused by the surface. While the radiative warping instability proposed by Pringle is promising for generating warps near luminous accreting objects, we expect that the wind-driven instability introduced here would dominate in objects that generate energetic outÑows