2002ApJ...575.1050P

We present the first orbital elements for the massive close binary HD 115071, a double-lined spectroscopic binary in a circular orbit with a period of 2.73135±0.00003 days. The orbital semiamplitudes indicate a mass ratio of M₂/M₁=0.58±0.02, and yet the stars have similar luminosities. We used a Doppler tomography algorithm to reconstruct the individual component optical spectra, and we applied well-known criteria to arrive at classifications of O9.5 V and B0.2 III for the primary and secondary, respectively. We present models of the Hipparcos light curve of the ellipsoidal variations caused by the tidal distortion of the secondary, and the best-fit model for a Roche-filling secondary occurs for an inclination of i=48°.7±2°.1. The resulting masses are 11.6±1.1 and 6.7±0.7M_☉ for the primary and secondary, respectively, so both stars are very overluminous for their mass. The system is one of only a few known semidetached, Algol-type binaries that contain O stars. We suggest that the binary has recently emerged from extensive mass transfer (possibly through a delayed contact and common-envelope process).