Stellar Systems Group

Sana, H.; Dunstall, P. R.; Hénault-Brunet, V.; Walborn, N. R.; de Koter, A.; de Mink, S. E.; Dufton, P. L.; Evans, C. J.; Maíz Apellániz, J.; Taylor, W. D.; Vink, J. S.
Proceedings of a Scientific Meeting in Honor of Anthony F. J. Moffat held at Auberge du Lac Taureau, St-Michel-Des-Saints, Québec, Canada, held 11-15 July 2011. ASP Conference Series, Vol. 465. San Francisco: Astronomical Society of the Pacific, p.284 (2012).
12/2012

ABSTRACT

We present the first results on the multiplicity and dynamics of the OB star population in 30 Dor obtained in the framework of the VLT-FLAMES Tarantula Survey. Based on their radial velocity (RV) variations, we have identified over 100 O-type and about 160 B-type spectroscopic binaries. The observed spectroscopic binary fraction for the O and B stars in our sample is of the order 30-35%. Preliminary considerations on the binary detection rate suggest a true spectroscopic binary fraction of the order of 50%. The overall RV dispersion (σ_RV) of the O stars in the complete sample is about 10 km s^-1 but we note that the NGC 2060 and NGC 2070 regions show slightly different dynamical properties. We identified 17 O-type runaway candidates that show deviating RVs. One third of these candidates are On/nn/nnn stars, indicating a large rotational velocity. We show that the fast rotators have different RV properties than the average of the sample and are distributed throughout the field. This suggests a link between large rotation rate and peculiar RVs and, ultimately, the runaway phenomenon. Using the O stars observed within 25″(˜ 6 pc) from the core of R136, we obtain a preliminary upper limit of 7.5 km s^-1 to σ_dyn. Given that this value has yet to be corrected down for contributions of non-detected long period binaries, this indicates that R136 is possibly a dynamically stable cluster.