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Astronomy & Astrophysics Letters

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, B-4000 Liège (Sart Tilman), 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

* Research Associate FNRS, Belgium
** Research Fellow FNRS, Belgium

+ Based on observations collected at the European Southern Observatory (La Silla, Chile).


     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 ± 4.0 and 68.8 ±3.8 M 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

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