[Previous] | [Session 95] | [Next]
E. Pfahl, S. Rappaport (MIT ), Ph. Podsiadlowski (Oxford), H. Spruit (MPA)
We investigate the statistical significance and implications of a new class of high-mass X-ray binaries (HMXBs), with Porb > 30 days and e < 0.2. The orbital parameters suggest that the neutron stars in these systems did not receive a very large kick at the time of formation. We develop a scenario wherein the neutron stars born in the new class of HMXBs receive kick speeds of only < 50 km/s, while neutron stars born in isolation and in low-mass X-ray binaries receive the conventional large kicks of 200-300 km/s. This apparent dichotomy may be explained if the kick speed depends on the rotation rate of the pre-collapse core, such that rapidly rotating core yield small kicks, and vice versa for slowly rotating cores.