Implications of massive close binaries for black hole formation and supernovae

The progenitor evolution of the massive X-ray binary Wray 977 is investigated using new models of massive close binary evolution. These models yield constraints on the mass limit for neutron star/black hole formation in single stars, MBH. We argue for quasi-conservative evolution in this system, and we find MBH > 13::21M from the existence of a neutron star in Wray 977, with the uncertainty being due to uncertainties in the treatment of convection. Our results revise earlier published much larger values of MBH derived from the parameters of Wray 977. Then, on the basis of a grid of 37 evolutionary models for massive close binaries with various initial masses, mass ratios and periods, we derive primary initial-final mass, initial mass- final helium core mass, and initial mass-final CO-core mass relations for the various mass transfer cases of close binary evolution. From these models we derive for single stars that MBH < 25M, independent of whether most black hole bina- ries formed through the Case A/B or the Case C binary channel. Using our grid of binary models, we obtain a consistent scenario for the formation of black holes in binary systems. We emphasize that in binaries the critical initial mass limits for neutron star/black hole formation and for white dwarf/neutron star formation are very different from the cor- responding values in single stars. While the first may well be above 100M in Case A/B binaries, the latter is found to be in the range 12...15M instead of the canonical value of 8...10 M usually quoted for single stars. This effect should not be ne- glected in population synthesis studies of massive binary sys- tems. Also, neutron star and black hole mass functions obtained for single stars can not per se compared to the masses of compact objects in binary systems. Massive close binaries produce also Type Ib and Ic super- novae. We find two different types of supernova progenitor structure in our models, one with remaining helium masses of the order of 1M which stems from an intermediate progeni- tor initial mass range (about 16...25 M), and another with one order of magnitude smaller remaining helium masses from ini- tial masses above and below this. A possible connection to the