Evolution of a (1+0.75) solar mass close binary system with mass exchange and gravitational radiation losses.

Abstract

The evolution of two low-mass close binary systems is followed numerically through the phase of mass exchange, both with and without the inclusion of gravitational radiation losses. In both systems, the primary, mass-losing components are initially homogeneous zero-age main-sequence stars of Populations I and II, respectively, whereas the secondary components are just assumed to be compact (i.e., white dwarfs, neutron stars, or black holes). It is found that gravitational radiation, via orbital angular-momentum losses, markedly influences the evolution of the system: (a) mass loss starts much earlier; and (b) the system spends a much longer time in the mass-exchange phase with, therefore, a smaller mass-transfer rate when compared with the case where gravitational radiation is neglected. The implications for observations are briefly discussed. In particular, these systems with white dwarfs as secondaries would constitute realistic models for cataclysmic variables, whereas if the compact component is a neutron star or black hole, the systems would be producing X-rays (L/sub x/approximately-less-than10/sup 36/ ergs s/sup -1/) for about 10/sup 10/ years and would constitute low-intensity globular cluster X-ray sources.