O-stars in VLT-FLAMES Tarantula Survey

The distribution of Vrot shows a two-component structure: a peak around 80km/s and a high-velocity tail extending up to ~600km/s. This structure is also present in the inferred distribution P(Veq) with around 80% of the sample having 0<Veq<=300km/s 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.

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.