Rotational Properties of the O-type Star Population in the Tarantula Region

The 30 Doradus (30 Dor) region in the Large Magellanic Cloud (also known as the Tarantula Nebula) is the nearest starburst region, containing the richest sample of massive stars in the Local Group. It is a perfect laboratory to investigate aspects of the formation and evolution of massive stars. Here, we focus on rotation which is a key parameter in the evolution of these objects. We establish the projected rotational velocity, v_{e}sini, distribution of an unprecendented sample of 216 radial velocity constant ΔRV ≤ 20 km s^{-1} O-type stars in 30 Dor observed in the framework of the VLT-FLAMES Tarantula Survey (VFTS). We also apply the  iterative deconvolution procedure of Lucy to infer the probability density, P(v_e), of the equatorial rotational velocity, v_ e. The distribution of v_{e}sini shows a two-component structure: a peak around 100 km s^{-1} and a high velocity tail extending up to 600 km s^{-1}. This structure is also present in the inferred probability distribution with around 75% of the sample having 0 ≤ v_{e} ≤ 240 km s^{-1} and the other 25% distributed in the high velocity region. The low velocity peak is consistent with that found in other studies of late-O and early-B stars. We conclusively identify a well populated high velocity tail containing two extremely fast rotators. The high velocity tail is compatible with expectations from binary interaction synthesis models and may be predominantly populated by post-binary interaction, spun up, objects. This may have important implications for the nature of progenitors of long-duration gamma ray bursts.status: publishe