WR20a: a massive cornerstone binary system comprising two extreme early-type stars

Abstract

We analyse spectroscopic observations of WR20a revealing that this star is a massive early-type binary system with a most probable orbital period of \sim 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 WR20a a cornerstone system for the study of massive star evolution.

5 pages, 3 figures, accepted by A&A Letters

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• Orbits of Four Very Massive Binaries in the R136 Cluster
• A multicolor CCD photometric study of the open clusters NGC 2866, Pismis 19, Westerlund 2, ESO96-SC04, NGC 5617 and NGC 6204

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