The Orbits of the γ-ray Binaries LS I +61 303 and LS 5039

Abstract

LS I +61 303 and LS 5039 are two of only a handful of known high-mass X-ray binaries (HMXBs) that exhibit very high energy emission in the MeV-TeV range, and these "γ-ray binaries" are of renewed interest due to the recent launch of the Fermi Gamma-ray Space Telescope. Here we present new radial velocities of both systems based on recent red and blue optical spectra. Both systems have somewhat discrepant orbital solutions available in the literature, and our new measurements result in improved orbital elements and resolve the disagreements. The improved geometry of each orbit will aid in studies of the high-energy emission region near each source. © 2009. The American Astronomical Society.