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arXiv · 1507.02286

The VLT-FLAMES Tarantula Survey XXI. Stellar spin rates of O-type spectroscopic binaries

O. H. Ramírez-Agudelo·H. Sana·S. E. de Mink·V. Hénault-Brunet·A. de Koter·N. Langer·F. Tramper·G. Gräfener·C. J. Evans·J. S. Vink·P. L. Dufton·W. D. Taylor
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Abstract

The initial distribution of spin rates of massive stars is a fingerprint of their elusive formation process. It also sets a key initial condition for stellar evolution and is thus an important ingredient in stellar population synthesis. So far, most studies have focused on single stars. Most O stars are however found in multiple systems. By establishing the spin-rate distribution of a sizeable sample of O-type spectroscopic binaries and by comparing the distributions of binary sub-populations with one another as well as with that of presumed single stars in the same region, we aim to constrain the initial spin distribution of O stars in binaries, and to identify signatures of the physical mechanisms that affect the evolution of the massive stars spin rates. We use ground-based optical spectroscopy obtained in the framework of the VLT-FLAMES Tarantula Survey (VFTS) to establish the projected equatorial rotational velocities (\vrot) for components of 114 spectroscopic binaries in 30 Doradus. The \vrot\ values are derived from the full-width at half-maximum (FWHM) of a set of spectral lines, using a FWHM vs. \vrot\ calibration that we derive based on previous line analysis methods applied to single O-type stars in the VFTS sample. The overall \vrot\ distribution of the primary stars resembles that of single O-type stars in the VFTS, featuring a low-velocity peak (at $\vrot < 200$ kms) and a shoulder at intermediate velocities ($200 < \vrot < 300$ kms). The distributions of binaries and single stars however differ in two ways. First, the main peak at $\vrot \sim$100 kms is broader and slightly shifted toward higher spin rates in the binary distribution compared to that of the presumed-single stars. Second, the \vrot distribution of primaries lacks a significant population of stars spinning faster than 300 kms while such a population is clearly present in the single star sample.

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O. H. Ramírez-Agudelo, H. Sana, S. E. de Mink, V. Hénault-Brunet, A. de Koter, N. Langer, F. Tramper, G. Gräfener, C. J. Evans, J. S. Vink, P. L. Dufton, W. D. Taylor. 2015-07-08. The VLT-FLAMES Tarantula Survey XXI. Stellar spin rates of O-type spectroscopic binaries. https://doi.org/10.1051/0004-6361%2F201425424

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