1997A&A...328..219S

We analyze the orbital motion of γ² Velorum based on high resolution optical spectra obtained in 1995 and 1996. By combining our data with values from the literature we find a period P=78.53±0.01d. We determine radial velocity semi-amplitudes K_WR=122±2km/s and K_O=38.4±2km/s for the Wolf-Rayet star and the O star, respectively. The given errors are the standard deviations of the results from individual lines. The inclination of the system is i=65°. This result is obtained by combining M_Osin³i from the orbital analysis with the mass M_O=29M_☉, obtained from its luminosity and stellar evolution tracks. The mass of the Wolf-Rayet component is M_WR=9M_☉. Our O star velocity curve disagrees by 15σ from a previously published result. We have identified the reason for the disagreement in the failure to correct for the WR emission that affects the measurements of the absorption line centers. The correction could have introduced systematic errors that may be larger than the given precision of the amplitudes. However, we can set an upper limit of K_O<50km/s from uncorrected measurements. This yields an upper limit for the Wolf-Rayet mass of M_WR<12M_☉. We find systematic phase-shifts between the velocity curves of some emission lines. We also observe that some (but not all) emission lines deviate significantly in the 1995 data set from the line's orbital solution defined by the 1996 observations. These phenomena may indicate that the radial velocities of the emission lines could be subject to systematic distortions and that the errors of the orbital motion are larger than the internal precision given here.