A Lifetime of Influence: Abstracts, Talks, and Posters
 

Rotational Velocities For Early Type Stars and the Relationship Between Rotation Speed and Density in Star-Forming Regions

S. C. Wolff
NOAO

S. E. Strom
NOAO

We present a summary of recent work aimed at characterizing the rotation speeds of young intermediate and high mass (2-30 solar masses) stars located in different environments. We present evidence that strongly suggests that the mean rotation speeds found among stars born in rich, dense bound clusters are significantly higher than those formed in loose, unbound associations. This difference is primarily the result of the paucity of slowly rotating stars in bound clusters. Our analysis of rotation properties among clusters and associations of differing ages suggests that the observed difference in mean rotation speed cannot be the result of evolution-driven changes in rotation speeds combined with a difference in the mean ages of the cluster and association samples.

We argue that the differences in the rotational properties of stars located in bound clusters and associations result primarily from differences in initial conditions, in particular, the higher turbulent speeds that characterize molecular gas located in high-density, cluster-forming regions. In turn, higher turbulent speeds likely lead to higher time-averaged accretion rates during the stellar assembly phase. In the context of stellar angular momentum regulation via "disk-locking," higher accretion rates result in both higher initial angular momenta and evolution-driven increases in surface rotation rates as stars contract from the birth line to the zero-age main sequence (ZAMS), thereby accounting for the higher rotation speeds of stars born in dense regions. If this explanation is correct, it suggests a direct link between initial conditions and outcome stellar properties - a result of potentially critical importance to guiding our understanding of how intermediate and high mass stars form.