1999A&A...345..163D

In this paper we demonstrate how previous determinations of the light ratio between the O and Wolf-Rayet stellar components of the γ Vel system are affected by large uncertainties. This is due, amongst other things, to the difficulty of measuring the equivalent widths of emission and absorption lines. We then present a new technique to de-blend and measure spectral lines, in which we compensate for the observed absorption features with synthetic profiles. From the new values of the diagnostic line strengths we determine a hotter spectral type for the O star companion (O7.5) than previously published. The light ratio is then determined, together with the stellar parameters, via a spectroscopic analysis. We obtain ΔM_V=1.47±0.13mag. From the light ratio and the system's luminosity we find M_V(O)=-5.14mag and M_V(WR)=-3.67mag. Simultaneously we determine T_eff(O)=35000K, L(O)=2.1x10⁵L_☉ and M(O)=30M_☉. An age of 3.59x10⁶yr is derived from these parameters and evolutionary tracks. We find that the H/He abundance ratio is solar. From a hydro-dynamical calculation of the radiation-driven wind we obtain {dot}(M)(O)=1.8x10^–7M☉/yr and v_∞(O)=2500km/s. From the O star mass derive from the literature we derive the mass of the Wolf-Rayet star, M(WR)=9M_☉. The mass-luminosity relation for Wolf-Rayet stars then leads to L(WR)=1.5x10⁵L_☉. We finally present the γ Vel Wolf-Rayet spectrum de-convolved from the O star in the range 3800-6700Å.