Dynamical Instabilities and Mass Exchange in Binary Systems

Abstract

A hydrodynamic scheme is presented by means of which the dynamical behaviour of stars transferring mass in semidetached binary systems may be investigated. Cool stellar envelopes are found to be dynamically unstable when in contact with the Roche lobe, but only so long as the recombination energy is sufficient to overcome the gravitational potential change to the surface. Such unstable states are followed by phases in which the photosphere shrinks inside the Roche lobe, readjusting to thermal equilibrium. The quasi-periodic mass transfer that results is suggested as being responsible for dwarf nova eruptions, and may be of importance in X-ray sources, Algol systems, and binary symbiotic variables.