A stellar audit: the computation of encounter rates for 47 Tucanae and ω Centauri

Abstract

Using King-Mitchie Models, we compute encounter rates between the various stellar species in the globular clusters ω Cen, and 47 Tuc. We also compute event rates for encounters between single stars and a population of primordial binaries. Using these rates, and what we have learnt from hydrodynamical simulations of encounters performed earlier, we compute the production rates of objects such as low-mass X-ray binaries (LMXBs), smothered neutron stars and blue stragglers (massive main-sequence stars). If 10 per cent of the stars are contained in primordial binaries, the production rate of interesting objects from encounters involving these binaries is as large as that from encounters between single stars. For example, encounters involving binaries produce a significant number of blue stragglers in both globular cluster models. The number of smothered neutron stars may exceed the number of LMXBs by a factor of 5–20, which may help explain why millisecond pulsars are observed to outnumber LMXBs in globular clusters.