Slow mass transfer in semidetached binaries

It is shown that, if the usual assumption of synchronous rotation (infinitely effective tidal coupling) in semidetached binary systems is replaced by that of detailed conservation of angular momentum with negligible tidal torques, the system is predicted to evolve in a qualitatively different manner after the onset of mass loss. For a wide range of mass ratios, initial mass transfer proceeds on a nuclear rather than a Kelvin time scale and the evolutionary track in the H-R diagram is significantly altered. It is suggested that the actual evolution of the system is determined by the time scale of tidal interaction and that the mass transfer rate probably lies between the classical values and those found here. Possible implications of the present results for X- ray sources such as HZ Her are discussed briefly. (AIP)