Rotational Velocities of Southern B Stars and a Statistical Discussion of the Rotational Properties

We have measured the projected rotational velocities of 1023 southern B stars listed in the Bright Star Catalog (BSC) and calibrated them against the 1975 Slettebak et al. system. We joined the sample with the 1091 mostly northern stars of the BSC whose projected rotational velocities were determined in the same way. There were 387 stars in common and with the sample of 1727 B type stars we found that the published values of V sin i for B dwarfs in the BSC average 30% higher than those derived using Slettebak et al. standards. Only 1.8% of the stars have projected rotational velocities larger than 300 km s-1 and 0.2% have V sin i larger than 350 km s-1. The mean projected rotational velocity is only 25% of break-up, implying that impending break-up is not a significant factor in reducing rotational velocities. We have found with the largest sample used up to now that the distribution in V for all B-type stars on the main sequence is bimodal.