The VLT-FLAMES Tarantula Survey XXII. Multiplicity properties of the B-type stars

• Published in: Astronomy and astrophysics (Berlin) Vol. 580; p. A93
• Main Authors: Dunstall, P R, Dufton, P L, Sana, H, Evans, C J, Howarth, I D, Simon-Diaz, S, de Mink, S E, Langer, N, Apellaniz, J Maiz, Taylor, W D
• Format: Journal Article
• Language: English
• Published: 01.08.2015
• Subjects: Astronomy; B stars; Clusters; Constants; Estimates; Magellanic clouds; Populations; Spectroscopy
• ISSN: 0004-6361; 1432-0746
• DOI: 10.1051/0004-6361/201526192

We investigate the multiplicity properties of 408 B-type stars observed in the 30 Doradus region of the Large Magellanic Cloud with multi-epoch spectroscopy from the VLT-FLAMES Tarantula Survey (VFTS). We use a cross-correlation method to estimate relative radial velocities from the helium and metal absorption lines for each of our targets. Objects with significant radial-velocity variations (and with an amplitude larger than 16 km s super(-1)) are classified as spectroscopic binaries. We find an observed spectroscopic binary fraction (defined by periods of <10 super(3,5)d and mass ratios >0.1) for the B-type stars, (obs) = 0.25 + or - 0.02, which appears constant across the field of view, except for the two older clusters (Hodge 301 and SL639). These two clusters have significantly lower binary fractions of 0.08 + or - 0.08 and 0.10 + or - 0.09, respectively. Using synthetic populations and a model of our observed epochs and their potential biases, we constrain the intrinsic multiplicity properties of the dwarf and giant (i.e. relatively unevolved) B-type stars in 30 Dor. We obtain a present-day binary fraction f sub(B)(true) = 0.58 + or - 0.11, with a flat period distribution. Within the uncertainties, the multiplicity properties of the B-type stars agree with those for the O stars in 30 Dor from the VFTS.