 Author

H. Sana
A. de Koter
S.E. de Mink
P.R. Dunstall
C.J. Evans
V. HénaultBrunet
J. Maíz Apellániz
O.H. RamírezAgudelo
W.D. Taylor
N.R. Walborn
J.S. Clark
P.A. Crowther
A. Herrero
M. Gieles
N. Langer
D.J. Lennon
J.S. Vink  Year
 2013
 Title
 The VLTFLAMES Tarantula Survey. VIII. Multiplicity properties of the Otype star population
 Journal
 Astronomy & Astrophysics
 Volume
 550
 Pages (fromto)
 A107
 Number of pages
 22
 Document type
 Article
 Faculty
 Faculty of Science (FNWI)
 Institute
 Anton Pannekoek Institute for Astronomy (API)
 Abstract

Context. The Tarantula Nebula in the Large Magellanic Cloud is our closest view of a starburst region and is the ideal environment to investigate important questions regarding the formation, evolution and final fate of the most massive stars.
Aims. We analyze the multiplicity properties of the massive Otype star population observed through multiepoch spectroscopy in the framework of the VLTFLAMES Tarantula Survey. With 360 Otype stars, this is the largest homogeneous sample of massive stars analyzed to date.
Methods. We use multiepoch spectroscopy and variability analysis to identify spectroscopic binaries. We also use a MonteCarlo method to correct for observational biases. By modeling simultaneously the observed binary fraction, the distributions of the amplitudes of the radial velocity variations and the distribution of the time scales of these variations, we constrain the intrinsic current binary fraction and period and massratio distributions.
Results. We observe a spectroscopic binary fraction of 0.35 ± 0.03, which corresponds to the fraction of objects displaying statistically significant radial velocity variations with an amplitude of at least 20 km s1. We compute the intrinsic binary fraction to be 0.51 ± 0.04. We adopt powerlaws to describe the intrinsic period and massratio distributions: f(log 10P/d) ~ (log 10P/d)π (with log 10P/d in the range 0.15−3.5) and f(q) ~ qκ with 0.1 ≤ q = M2/M1 ≤ 1.0. The powerlaw indexes that best reproduce the observed quantities are π = −0.45 ± 0.30 and κ = −1.0 ± 0.4. The period distribution that we obtain thus favours shorter period systems compared to an Öpik law (π = 0). The mass ratio distribution is slightly skewed towards low mass ratio systems but remains incompatible with a random sampling of a classical mass function (κ = −2.35). The binary fraction seems mostly uniform across the field of view and independent of the spectral types and luminosity classes. The binary fraction in the outer region of the field of view (r > 7.8′, i.e. ≈117 pc) and among the O9.7 I/II objects are however significantly lower than expected from statistical fluctuations. The observed and intrinsic binary fractions are also lower for the faintest objects in our sample (Ks > 15.5 mag), which results from observational effects and the fact that our O star sample is not magnitudelimited but is defined by a spectraltype cutoff. We also conclude that magnitudelimited investigations are biased towards larger binary fractions.
Conclusions. Using the multiplicity properties of the O stars in the Tarantula region and simple evolutionary considerations, we estimate that over 50% of the current O star population will exchange mass with its companion within a binary system. This shows that binary interaction is greatly affecting the evolution and fate of massive stars, and must be taken into account to correctly interpret unresolved populations of massive stars.  URL
 go to publisher's site
 Language
 English
 Permalink
 http://hdl.handle.net/11245/1.404300
Disclaimer/Complaints regulations
If you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library, or send a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible.