Fundamental Stellar Parameters of γ[TSUP]2[/TSUP] Velorum from [ITAL]HIPPARCOS[/ITAL] Data

Abstract

We report parallax measurements by the HIPPARCOS satellite of γ2 Velorum and a few related objects. The distance of γ2 Vel is d = 258 -->+ 41−31 pc, significantly smaller than the commonly adopted value to Vela OB2. For ζ Puppis d = 429 -->+ 120−77 pc is in agreement with the canonical distance. The total mass of γ2 Vel derived from its parallax, the angular size of the semimajor axis as measured with intensity interferometry, and the period are M(W-R + O) = 29.5 ± 15.9 M☉. This result favors the orbital solution of Pike et al. over that of Moffat et al. The stellar parameters for the O star companion derived from line-blanketed non-LTE atmosphere models are Teff = 34,000 ± 1500 K, log L/L☉ = 5.3 ± 0.15, from which an evolutionary mass of M = 29 ± 4 M☉ and an age of 4.0 -->+ 0.8−0.5 Myr is obtained from single-star evolutionary models. With non-LTE model calculations including He and C, we derive a luminosity log L/L☉ ~ 4.7 ± 0.2 for the W-R star. The mass-luminosity relation of hydrogen-free W-R stars implies a mass of MW-R ~ 5 ± 1.5 M☉. From our data we favor an age of about 10 Myr for the bulk of the Vela OB2 stars. Evolutionary scenarios for ζ Pup and γ2 Vel are discussed in the light of our results.