THE GROWTH-RATE OF TIDALLY EXCITED WAVES IN ACCRETION DISKS

Accretion disks in close binary systems are subject to a tidally drive n parametric instability that leads to the growth of internal waves ne ar the outer edges of such disks. These waves are important in underst anding the torque exerted on a disk by tidal forces and may play a rol e in the structure of the disk at small radii. Here we calculate the g rowth rate of this instability, including the effects of vertical stru cture and fluid compressibility. We find growth rates that are only sl ightly different from Goodman's original results, except that near the vertical resonance radius the growth rate can have an extremely broad and strong peak when the disk is stably stratified in the vertical di rection. Higher order modes, in the sense of increasing number of vert ical nodes, have similar growth rates. Our results differ from a previ ous calculation along these lines by Lubow et al. The difference is mo stly due to their neglect of radial gradients in the tidally distorted streamlines.