Kinematics, close binary evolution, and ages of the O stars

Abstract

Accurate proper motions were determined for O4-B2 stars, Wolf-Rayets, and B9-K3 supergiants. Space velocities were calculated for these stars and used to investigate the kinematics of the O stars. Observations suggest that the group H stars were produced from mass exchange in massive close binary (MCB) systems, and the high space velocities typical of these stars were caused by binary supernovae. Hence, 50% of the O stars were probably produced by mass accretion in MCS systems. A model is presented describing the evolution of a MCB system for the case of no mass loss from the system: (1) for stars exploding as supernovae, 15% of the initial stellar mass will form a collapsed remnant, (2) stars with masses at least equal to 12 solar masses will eventually explode as supernovae, and (3) the group H stars with masses greater than 45 solar masses probably have black hole binary companions.