AAS 199th meeting, Washington, DC, January 2002
Session 5. Stellar and Intermediate Mass Black Holes
Display, Monday, January 7, 2002, 9:20am-6:30pm, Exhibit Hall

## [5.04] The Origin and Nature of the Microquasar LS 5039

M.V. McSwain, D.R. Gies (GSU), R.L. Riddle (ISU), Z. Wang (MIT ), D.W. Wingert (GSU)

LS 5039 is a relatively faint (V = 11.2) and hot star (O7 V) that is one of only four confirmed massive X-ray binaries with associated radio emission. It also has radio-emitting relativistic jets characteristic of galactic microquasars and probably high energy gamma ray emission as well. We recently determined that the system is a short period (P = 4.117 ±0.011 days) binary with the highest known eccentricity (e = 0.41 ±0.05) among O star binaries with comparable periods (McSwain et al. 2001). The system's large eccentricity and high rotational velocity (V\sin i = 131 ±6 km~s-1) indicate that this is likely a youthful system, and it presents a unique opportunity to study the early evolution of MXRBs.

The high eccentricity of the system also indicates that it must have undergone significant mass loss during the supernova that created the compact companion. Here we present constraints on the original system based on the period, eccentricity, and probable masses (Bhattacharya & van den Heuvel 1991; Nelemans et al. 1999). We estimate that the progenitor lost at least 15 M\odot during the supernova event and that the original period was \approx 1.6 days.