High Mass X-Ray Binary Population Synthesis
Session 65 -- Interacting Binaries: Compact Stars
Oral presentation, Thursday, January 13, 2:15-3:45, Salon V Room (Crystal Gateway)

## [65.01] High Mass X-Ray Binary Population Synthesis

W. W. Dalton, C. L. Sarazin (University of Virginia)

Using modern theoretical stellar evolutionary tracks (Schaller {{\it et al.} \ }1992), we have constructed a library of massive binary evolutions consisting of 28 initial primary masses ranging from 11 to 95 ${ {\,M_\odot} }$ and 30 initial secondary masses ranging from 5 to 90 ${ {\,M_\odot}}$. Each system is evolved from 12 possible starting separations (resulting in a library of 5544 starting configurations) through the following stages: mass loss (via stellar wind and Roche lobe overflow), mass exchange (and common envelope mass ejection, should it occur), the supernova of the primary, X-ray emission from accretion onto the resultant compact object from the companion star (either via stellar wind accretion or Roche lobe overflow).

By assuming an initial mass function and a star formation history for the Galactic disk and applying observed massive binary characteristics (the distribution of mass ratios, the distribution of binary separations, and the binary fraction), we model the present day Galactic high mass X-ray binary (HMXRB) population.

In our models we have varied the fraction ({\it{f}} \ ) of overflow matter that escapes the system during mass exchange. We find that the observable number of bright HMXRB is essentially constant for $0.3 < f < 0.7$. The primary consequence of increasing the mass loss from these systems is to reduce the mean period for bright sources.

We have also run models of the HMXRB population designed to test the mechanism for the X-ray emission in HMXRB. In the first case we have assumed that all of the emission is the result of accretion onto the compact object from the companions spherically symmetric wind. In the second case we initially assume accretion from a spherically symmetric wind, but as the mass losing star fills its Roche volume we employ a simplified model to account for the formation of an accretion disk. We find that in the case of pure wind accretion, the number of very luminous (X-ray luminosity in excess of ${10^{37}} \, \rm{erg} \, \rm{s}^{-1}$) sources produced falls short of the number implied by observations. We find much better agreement in the second case, where accretion disk formation is taken into account.