Long-term Periodicities and Accretion Disks

• Several well-known long-term periodicities in X-ray binaries (Her X-1, SS 433) can be explained via a tilted or warped accretion disk precessing at a single frequency from the inner to outer disk,

• Many candidate systems with long-term periodicities (LMC X-4, Cyg X-1, XB 1820-303, Cyg X-2, etc.),

• Radiation-driven warping instability (Pringle, 1997), one mechanism for exciting a global disk warp, shows nonlinear behavior over a realistic range of system parameters.