Rotational Velocities of B Stars

Abstract

We measured projected rotational velocities for nearly 1100 B stars with these results. (1) They average substantially less than those published in the Bright Star Catalogue and are about one-quarter of the break-up velocities. (2) For the late B stars the deconvolved distribution in V is bimodal; one lobe consists of rapidly-rotating normal stars and and the other lobe of slowly-rotating Ap stars. This is consistent with diffusion theory by Michaud. (3) Using interior models by Bertelli et al. we predicted rotational velocities of giants and found that they agree with observational ones for rigid-body rotation. Combining this with other data, we conclude that if the expansion of post-main sequence stars is a factor of < 4, the conservation of angular momentum is by rigid-body rotation but for factors > 4, it is in shells. (4) In binaries the primaries have synchronized rotational and orbital motions for periods < 2.4 days. For the A stars studied by Abt & Morrell the limit is 5.0 days. (5) In binaries the orbits are circularized for periods < 1.5 days and for A star < 2.5 days. For binaries of 10^7.5 — 10^10.2 yr the maximum circularized period is 0.0016 A ^0.40 days.