Optical spectroscopy of X-Mega targets - II. The massive double-lined O-type binary HD 93205

A new high-quality set of orbital parameters for the O-type spectroscopic binary HD 93205 has been obtained combiningand coude CCD observations. The radial velocity orbits derived from the He ii �4686u (primary component) and He i �4471u (secondary component) absorption lines yield semiamplitudes of 133±2 and 314±2 kms −1 for each binary component, resulting in minimum masses of 31 and 13 M⊙ (q = 0.42). We also confirm for the binary components the spectral classification of O3V + O8V previously assigned. Assuming for the O8V component a "normal" mass of 22 - 25 M⊙ we would derive for the primary O3V a mass of "only" 52 - 60 M⊙ and an inclination of about 55 ◦ for the orbital plane. We have also determined for the first time a period of apsidal motion for this system, namely 185 ± 16 years using all available radial velocity data-sets of HD 93205 (from 1975 to 1999). Phase-locked variations of the X-ray emission of HD 93205 consisting of a rise of the observed X-ray flux near periastron passage, are also discussed.