Session 79 - Special Objects in the Galaxy.
Oral session, Thursday, June 11
We present the results of a linearized perturbation analysis of the disk and boundary layer (BL) in cataclysmic variables. In the BL, for the case of large-scale, azimuthal oscillations, we find a triplet of torsional modes consisting primarily of a perturbation of the azimuthal velocity, and a singlet mode consisting primarily of a pressure perturbation. Two of these, which we call the fast torsional modes,'' have rise times short enough for significant amplification of a perturbation entering the BL. They are gravity modes, modified by the large shear and radial acceleration in the BL. The instability is caused by the increase in the inertial force experience by a parcel of accreting material with a perturbed velocity.