Gas dynamics of semidetached binaries

Abstract

The gas dynamics of semidetached binary systems is analyzed in the context of the Roche model. It is shown that the steady flow can be formulated in terms of a problem with multiple length scales if it is assumed that the contact component rotates synchronously and the flow occurs isothermally with the thermal speed being a small fraction of the relative orbital speed of the two stars. This concept and semianalytical methods are used to demonstrate that material escapes from the surface of the contact component in a highly anisotropic stellar wind, that the wind throttles into a narrow stream of material whose width is a function of the orbital separation and whose density is a function of the mass transfer rate and the relative orbital speed of the two stars, and that the stream results in the formation of a disk of material of prescribed size orbiting the detached component if the latter is smaller than a specified size.