The spectrum of the very massive binary system WR 20a (WN6ha + WN6ha): Fundamental parameters and wind interactions

Details The spectrum of the very massive binary system WR 20a (WN6ha + WN6ha): Fundamental parameters and wind interactions The spectrum of the very massive binary system WR 20a (WN6ha + WN6ha): Fundamental parameters and wind interactions

Mar 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005a%26a...432..985r&link_type=abstract

Astronomy and Astrophysics, Volume 432, Issue 3, March IV 2005, pp.985-998

Astronomy and Astrophysics

Astrophysics

54

Stars: Binaries: Spectroscopic, Stars: Early-Type, Stars: Fundamental Parameters, Stars: Individual: Wr 20A, Stars: Wolf-Rayet

Scientific paper

We analyse the optical spectrum of the very massive binary system WR 20a (WN6ha + WN6ha). The most prominent emission lines, Hα and He ii λ 4686, display strong phase-locked profile variability. From the variations of their equivalent widths and from a tomographic analysis, we find that part of the line emission probably arises in a wind interaction region between the stars. Our analysis of the optical spectrum of WR 20a indicates a reddening of AV ≃ 6.0 mag and a distance of 7.9 kpc, suggesting that the star actually belongs to the open cluster Westerlund 2. The location of the system at ˜ 1.1 pc from the cluster core could indicate that WR 20a was gently ejected from the core via dynamical interactions. Using a non-LTE model atmosphere code, we derive the fundamental parameters of each component: Teff = 43 000 ± 2000 K, log{Lbol/L&sun;} ≃ 6.0, dot{M} = 8.5 × 10-6 M&sun; yr-1 (assuming a clumped wind with a volume filling factor f = 0.1). Nitrogen is enhanced in the atmospheres of the components of WR 20a, while carbon is definitely depleted. Finally, the position of the binary components in the Hertzsprung-Russell diagram suggests that they are core hydrogen burning stars in a pre-LBV stage and their current atmospheric chemical composition probably results from rotational mixing that might be enhanced in a close binary compared to a single star of same age.
Based on observations collected at the European Southern Observatory, La Silla, Chile.

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