Rotational synchronisation of B-type binaries in 30 Doradus

Abstract

The spin evolution of stars in close binary systems can be strongly affected by tides. We investigate the rotational synchronisation of the stellar components for 69 SB1 systems and 14 SB2 B-type systems in the 30 Doradus region of the Large Magellanic Cloud using observations from the VFTS and BBC surveys. Their orbital periods range from a few to a few hundred days, while estimated primary masses for these systems are in the range ∼5−20 M_{⊙ with mass ratio ranges of q ∼ 0.03 − 0.5 and q ∼ 0.6 − 1.0 for the SB1 and SB2 systems, respectively. Projected rotational velocities of the stellar components have been compared with their synchronous velocities derived from the orbital periods. We find that effectively all systems with an orbital period of more than 10 days must be asynchronous, whilst all the systems with periods of less than 3 days are likely synchronised. In terms of the stellar fractional radius (r), our results imply that all systems with r < 0.1 are asynchronous, with those having r > 0.2 probably being synchronised. For the apparently synchronised systems, our results are more consistent with synchronisation at the mean orbital angular velocity rather than with that at periastron.}