Rotational Velocities For B0-B3 Stars in 7 Young Clusters: Further Study of the Relationship between Rotation Speed and Density in Star-Forming Regions

We present the results of a study aimed at assessing the differences in the dis- tribution of rotation speeds, N (v sin i) among young (1-15 Myr) B stars spanning a range of masses 6 < M/M < 12 and located in different environments: 7 low density (rho < 1 M /pc^3) ensembles that are destined to become unbound stellar associations, and 8 high density (rho >> 1 M /pc^3) ensembles that will survive as rich, bound stellar clusters for ages well in excess of 10^8 years. Our results demonstrate (1) that independent of environment, the rotation rates for stars in this mass range do not change by more than 0.1 dex over ages t ~ 1 to t ~ 15 Myr; and (2) that stars formed in high density regions lack the cohort of slow rotators that dominate the low density regions and young field stars. We suggest that the differences in N(v sin i) between low and high density regions may reflect a combination of initial conditions and environmental effects: (1) the higher turbulent speeds that characterize molecular gas in high density, cluster- forming regions; and (2) the stronger UV radiation fields and high stellar densities that characterize such regions.