Linear stability analysis of spherical accretion flows onto compact objects

Abstract

The steady state structure and linear stability of spherical accretionflows onto compact objects are investigated over a wide range ofaccretion rates (ARs) for a variety of cooling functions as a functionof the ratio of specific heats (gamma). Both radial and nonradial shockperturbations are considered. The flows become more extended as ARdecreases. The cooling function has a significant effect on the extendedstructure of settling solutions with gamma = 5/3. In contrast, theextended structure of settling solutions with gamma = 4/3 is nearlyindependent of the form of the cooling function. For both gamma = 4.3and gamma = 5.3, radial shock oscillation in the fundamental and firstovertone modes are destabilized in spherically extended accretionenvelopes. The application of these results to postsupernova neutronstar accretion flows and to luminosity oscillations in AM Her objectsare discussed.