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Astron. Astrophys. 345, 163-171 (1999)


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The [FORMULA] Velorum binary system

I. O star parameters and light ratio

Orsola De Marco and W. Schmutz

Institut für Astronomie, ETH-Zentrum, Scheuchzerstrasse 7, CH-8092 Zürich, Switzerland

Received 27 August 1998 / Accepted 9 February 1999

Abstract

In this paper we demonstrate how previous determinations of the light ratio between the O and Wolf-Rayet stellar components of the [FORMULA] 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 [FORMULA]=1.47[FORMULA]0.13 mag. From the light ratio and the system's luminosity we find [FORMULA](O) = -5.14 mag and [FORMULA](WR) = -3.67 mag. Simultaneously we determine [FORMULA](O) = 35 000 K, L(O) = 2.1[FORMULA]105 [FORMULA] and [FORMULA](O) = 30 M[FORMULA]. An age of 3.59[FORMULA]106 yr 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 [FORMULA](O) = 1.8[FORMULA]10-7 M[FORMULA] yr-1 and [FORMULA](O) = 2500 km s-1.

From the O star mass derived here and the mass ratio from the literature we derive the mass of the Wolf-Rayet star, [FORMULA](WR) = 9 M[FORMULA]. The mass-luminosity relation for Wolf-Rayet stars then leads to L(WR) = 1.5[FORMULA]105 [FORMULA]. We finally present the [FORMULA] Vel Wolf-Rayet spectrum de-convolved from the O star in the range 3800-6700 Å.

Key words: stars: binaries: spectroscopic – stars: early-type – stars: fundamental parameters – stars: individual: fl Vel – stars: Wolf-Rayet

Send offprint requests to: orsola@astro.phys.ethz.ch

© European Southern Observatory (ESO) 1999

Online publication: April 12, 1999

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