RADIATION-DRIVEN WARPING - THE ORIGIN OF WARPS AND PRECESSION IN ACCRETION DISKS

A geometrically thin, optically thick, warped accretion disk with a ce ntral source of luminosity is subject to nonaxisymmetric forces due to radiation pressure; the resulting torque acts to modify the warp. In a recent paper, J.E. Pringle used a local analysis to show that initia lly planar accretion disks are unstable to warping that is driven by r adiation torque. Here we extend this work with a global analysis of th e stable and unstable modes. We confirm Pringle's conclusion that thin , centrally illuminated accretion disks are generically unstable to wa rping via this mechanism; we discuss the time evolution and likely ste ady state of such systems, and show specifically that this mechanism c an explain the warping of the disk of water masers in NGC 4258 and the 164 day precession period of the accretion disk in SS 433. Radiation- driven warping and precession provide a robust mechanism for producing warped, precessing accretion disks in active galactic nuclei and X-ra y binary systems.