Rotational velocities of A-type stars

Abstract

Context. In previous works of this series, we have shown that late B-and early A-type stars have genuine bimodal distributions of rotational velocities and that late A-type stars lack slow rotators. The distributions of the surface angular velocity ratio / crit ( crit is the critical angular velocity) have peculiar shapes according to spectral type groups, which can be caused by evolutionary properties. Aims. We aim to review the properties of these rotational velocity distributions in some detail as a function of stellar mass and age. Methods. We have gathered v sin i for a sample of 2014 B6-to F2-type stars. We have determined the masses and ages for these objects with stellar evolution models. The (T eff , log L/L )-parameters were determined from the uvby- photometry and the HIPPARCOS parallaxes.