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Issue A&A
Volume 420, Number 2, June III 2004
Page(s) L9 - L13
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:20040150



A&A 420, L9-L13 (2004)
DOI: 10.1051/0004-6361:20040150

Letter

WR 20a: A massive cornerstone binary system comprising two extreme early-type stars

G. Rauw1, M. De Becker1, Y. Nazé1, P. A. Crowther2, E. Gosset1, H. Sana1, K. A. van der Hucht3, 4, J.-M. Vreux1 and P. M. Williams5

1  Institut d'Astrophysique et de Géophysique, Université de Liège, Allée du 6 Août, Bât. B5c, 4000 Liège, Belgium
2  Department of Physics & Astronomy, University of Sheffield, Hicks Building, Hounsfield Rd., Sheffield S3 7RH, UK
3  SRON National Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
4  Astronomical Institute Anton Pannekoek, University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
5  Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK

(Received 25 March 2004 / Accepted 25 April 2004)

Abstract
We analyse spectroscopic observations of WR 20a revealing that this star is a massive early-type binary system with a most probable orbital period of ~ 3.675 days. Our spectra indicate that both components are most likely of WN6ha or O3If */WN6ha spectral type. The orbital solution for a period of 3.675 days yields extremely large minimum masses of $70.7\,\pm\,4.0$ and $68.8 \pm 3.8~M_{\odot}$ for the two stars. These properties make WR 20a a cornerstone system for the study of massive star evolution.


Key words: binaries: spectroscopic -- stars: early-type -- stars: fundamental parameters -- stars: individual: WR 20a

Offprint request: G. Rauw, rauw@astro.ulg.ac.be

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© ESO 2004


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