Wolf-Rayet stars and relativistic objects: Distinctions between the mass distributions in close binary systems

The observed properties of Wolf-Rayet stars and relativistic objects in clo se hi nary systems are analyzed. The final masses M-CO(f) for the carbon-ox ygen cores of WR stars in WR + O binaries are calculated taking into accoun t the radial loss of matter via stellar wind, which depends on the mass of the star. The analysis includes new data on the clumpy structure of WR wind s, which appreciably decreases the required mass-loss rates (M) over dot(WR ) for the WR stars. The masses M-CO(f) lie in the range (1-2)M.-(20-44)M. a nd have a continuous distribution. The masses of the relativistic objects M -x are 1-20M. and have a bimodal distribution: the mean masses for neutron stars and black holes are 1.35 +/- 0.15M. and 8-10M., respectively, with a gap from 2-4M. in which no neutron stars or black holes are observed in clo se binaries. The mean fnal GO-core mass is (M) over bar (f)(CO) = 7:4-10.3M ., close to the mean mass for the black holes. This suggests that it is not only the mass of the progenitor that determines the nature of the relativi stic object, but other parameters as well-rotation, magnetic field, etc. On e SBIR Wolf-Rayet binary and 11 suspected WR + C binaries that may have low -mass companions (main-sequence or subgiant M-A stars) are identified; thes e could be the progenitors of low-mass X-ray binaries with neutron stars an d black holes. (C) 2001 MAIK "Nauka/Interperiodica".