The VLT-FLAMES Tarantula Survey XII. Rotational velocities of the single O-type stars

O.H. Ram'{i}rez-Agudeloinst{1},
S. Sim'on-D'{i}az inst{2,3},
H. Sana inst{1,4},
A. de Koter inst{1,5},
C. Sab'{i}n-Sanjul'{i}an inst{2,3},
S.E. de Mink inst{6,7},
P. L. Dufton inst{8},
G. Gr"afener inst{9},
C.J. Evans inst{10},
A. Herrero inst{2,3},
N. Langer inst{11},
D.J. Lennon inst{12},
J. Ma'{i}z Apell'aniz inst{13},
N. Markova inst{14},
F. Najarro inst{15},
J. Puls inst{16},
W.D. Taylor inst{10},
J.S. Vink inst{9}

^{1} Astronomical Institute Anton Pannekoek, Amsterdam University, Science Park 904, 1098~XH, Amsterdam, The Netherlands
^{2} nstituto de Astrof'{i}sica de Canarias, C/ V'{i}a L'{a}ctea s/n, E-38200 La Laguna, Tenerife, Spain
^{3} Departamento de Astrof'{i}sica, Universidad de La Laguna, Avda. Astrof'{i}sico Francisco S'{a}nchez s/n, E-38071 La Laguna, Tenerife, Spain
^{4} Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
^{5} Instituut voor Sterrenkunde, Universiteit Leuven, Celestijnenlaan 200 D, 3001, Leuven, Belgium
^{6} Observatories of the Carnegie Institution for Science, 813 Santa Barbara St, Pasadena, CA 91101, USA
^{7} Cahill Center for Astrophysics, California Institute of Technology, Pasadena, CA 91125, USA
^{8} Astrophysics Research Centre, School of Mathematics and Physics, Queen's University of Belfast, Belfast BT7 1NN, UK
^{9} Armagh Observatory, College Hill, Armagh, BT61 9DG, Northern Ireland, UK
^{10} UK Astronomy Technology Centre, Royal Observatory Edinburgh, Blackford Hill, Edinburgh, EH9 3HJ, UK
^{11} Argelander-Institut f"ur Astronomie, Universit"at Bonn, Auf dem H"ugel 71, 53121 Bonn, Germany
^{12} European Space Astronomy Centre (ESAC), Camino bajo del Castillo, s/n Urbanizacion Villafranca del Castillo, Villanueva de la Ca~nada, E-28692 Madrid, Spain
^{13} nstituto de Astrof'{i}sica de Andaluc'{i}a-CSIC, Glorieta de la Astronom'ia s/n, E-18008 Granada, Spain
^{14} Institute of Astronomy with NAO, Bulgarian Academy of Science, PO Box 136, 4700 Smoljan, Bulgaria
^{15} Centro de Astrobiolog'{i}a (CSIC-INTA), Ctra. de Torrej'on a Ajalvir km-4, E-28850 Torrej'on de Ardoz, Madrid, Spain
^{16} Universit"atssternwarte, Scheinerstrasse 1, 81679 M"unchen, Germany

% context heading (optional)
% {} leave it empty if necessary resultsssss
{The 30 Doradus (30,Dor) region of the Large Magellanic Cloud, also known as the Tarantula Nebula, is the nearest starburst region. It contains the richest population of massive stars in the Local Group and it is thus
the best possible laboratory to investigate open questions in the formation and evolution of massive stars.}
% aims heading (mandatory)
{Using ground based multi-object optical spectroscopy obtained in the framework of the VLT-FLAMES Tarantula Survey (VFTS), we aim to establish the (projected) rotational velocity distribution for a sample of 216 presumably single O-type stars in 30 Dor. The size of the sample is large enough to obtain statistically significant information and to search for variations among sub-populations -- in terms of spectral type, luminosity class, and spatial location -- in the field of view.}
% methods heading (mandatory)
{We measured projected rotational velocities, vrot, by means of a Fourier transform method and a profile fitting
method applied on a set of isolated spectral lines. We also used an iterative deconvolution procedure to infer the probability density,
$rm{P(veq)}$, of the equatorial rotational velocity, veq.}
% results heading (mandatory)
{The distribution of vrot shows a two-component structure: a peak around 80~kms
and a high-velocity tail extending up to $sim$600 kms. This structure is also present in the inferred distribution $rm{P(veq)}$
with around 80% of the sample having 0 $<$ veq, $leq, 300$~kms and the other 20% distributed in the high-velocity
region. The presence of the low-velocity peak is consistent with that found in other studies for late O- and early B-type stars. }
% conclusions heading (optional), leave it empty if necessary
{Most of the stars in our sample rotate with a rate less than 20% of their break-up velocity.
For the bulk of the sample, mass-loss in a stellar wind and/or envelope expansion is not efficient enough
to significantly spin down these stars within the first few Myr of evolution. If massive-star formation
results in stars rotating at birth with a large fraction of their break-up velocities, an alternative
braking mechanism, possibly magnetic fields, is thus required to explain the present day rotational
properties of the O-type stars in 30,Dor. The presence of a sizeable population of fast rotators is
compatible with recent population synthesis computations that investigate the influence of binary evolution
on the rotation rate of massive stars. Despite the fact that we have excluded stars that show significant
radial velocity variations, our sample may have remained contaminated by post-interaction binary products.
The fact that the high-velocity tail may be preferentially (and perhaps even exclusively), populated by
post-binary interaction products, has important implications for the evolutionary origin of systems
that produce gamma-ray bursts.

Reference: A&A (in press)
Status: Manuscript has been accepted


Comments: Accepted for publication in Astronomy & Astrophysics