On the progenitors of double neutron star systems
Received 6 November 1996 / Accepted 20 November 1996
We discuss models for calculating the late stages of high-mass binary evolution. Our discussion is based on evolutionary calculations for initial binaries composed of a main-sequence star of mass range 8 to 30 with a neutron star companion. The evolution of the primary is followed with the grids of Schaller et al. (1992) until the two stars interact, and simple analytic fits for helium and carbon-oxygen stars. For non-conservative mass transfer phases, two physical processes are considered: ejection of the excess overflowing matter in the form of jets from the neutron star and common envelope (CE) evolution. For each model, the code allows us to find the progenitors of the four known double neutron star systems (NS-NS) in the disk of the Galaxy. We show that the observed parameters of PSR 1913+16 and PSR 1534+12 are consistent with one or two stages of mass transfer. In contrast, the wide orbits of PSR 2303+46 and PSR J1518+49 are the most difficult to reproduce since a moderate orbital shrinkage is required through a CE phase. In particular, the likelihood of the formation of PSR J1518+49 appears to be very sensitive to the adopted formalism for CE-evolution.
Key words: stars: close binaries stars: evolution stars: mass loss neutron stars WR stars
© European Southern Observatory (ESO) 1997
Online publication: June 5, 1998