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 T_eff = 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 M_W-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.

Subject headings: stars: distances; stars: early-type; stars: fundamental parameters; stars: mass loss; stars: Wolf-Rayet

^* Based on data from the ESA HIPPARCOS astrometry satellite.

Print publication: Issue 2 (1997 August 1)
Received 1997 March 11, accepted for publication 1997 May 22