Nonaxisymmetricg‐Mode andp‐Mode Instability in a Hydrodynamic Thin Accretion Disk

It has been suggested that quasi-periodic oscillations of accreting X-raysources may relate to the modes named in the title. We considernon-axisymmetric linear perturbations to an isentropic, isothermal,unmagnetized thin accretion disk. The radial wave equation, in which the numberof vertical nodes (n) appears as a separation constant, admits a wave-actioncurrent that is conserved except, in some cases, at corotation. Waves withoutvertical nodes amplify when reflected by a barrier near corotation. Theiraction is conserved. As was previously known, this amplification allows the n=0modes to be unstable under appropriate boundary conditions. In contrast, wefind that waves with n >0 are strongly absorbed at corotation rather thanamplified; their action is not conserved. Therefore, non-axisymmetric p-modesand g-modes with n>0 are damped and stable even in an inviscid disk. Thiseliminates a promising explanation for quasi-periodic oscillations inneutron-star and black-hole X-ray binaries.Comment: A new version of the paper. The technical error in version 1 has been correcte