POPULATION SYNTHESIS OF HIGH-MASS BINARIES

We present a model for the evolution of a population of single stars a nd binaries, in which the eccentricity of initial binaries and mass tr ansfer between the binary components are taken into account. To illust rate the model, we apply it to the formation of neutron stars, both si ngle and in binaries. The eccentricity of primordial binaries allows a wide, non-interacting binary to survive the first and second supernov ae in many more cases than suggested by previous calculations that ass ume circular orbits. Mass transfer in binaries enhances the rate of ty pe I supernovae with respect to that of the type II supernovae. A siza ble fraction of initial binaries merge into a single star; 10 - 15 % o f the type II supernovae are from such mergers. Models in which neutro n stars receive a kick velocity at birth predict birth rates for wide and close radio-pulsar binaries, and for high-mass (including Be-) X-r ay binaries that are roughly in agreement with observations. All our m odels produce too many Her X-1 type binaries. The formation rate of ra dio-pulsars that remain in a binary after the first supernova explosio n and are released at the second supernova event is predicted by our m odels to be comparable to the formation rate of recycled binary radio pulsars, i.e. less than a few per cent of the formation rate of single radio pulsars.