The Hipparcos distance determination of the Wolf-Rayet system gamma(2) Velorum (WC8+O) and its ramifications

Hipparcos parallax measurements give a distance to the Wolf-Rayet WC8 + O spectroscopic binary gamma(2) Vel of d = 258(-31)(+41) pc and a distance to the O4I(n)f star zeta Pup of d = 429(-77)(+120) pc. Adopting for gamma(2) Vel an interstellar extinction of A(v) = 0.06 mag, this implies an absolute magnitude M-v = -5.4 mag for the WC8 + O binary system. Given that the binary components have a magnitude difference Delta m = 1.4 mag, we derive M-v(WC8) = -3.7 and M-v(O) = -5.0 mag. The latter indicates an 08.5III rather than an O9I companion, as was adopted during the last 25 years. Apparently gamma(2) Vel is not a member of, but a foreground object before the open cluster Cr173 and the association Vel OB2. Given a re-assessment of the distance of the Gum Nebula, gamma(2) Vel is still one of its ionizing sources, while zeta Pup appears to be located at the back of the Gum Nebula. Consequences of the Hipparcos distance determination of gamma(2) Vel for its mass, mass loss rate, luminosities at various wavelengths, and, briefly, its association with the Gum Nebula, are discussed. (C) 1997 Elsevier Science B.V

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