Astronomy Colloquium

Stellar rotation is intimately connected to some of the most challenging problems in stellar astrophysics: the star and planet formation processes, the origin and generation of magnetic fields, and the transport of angular momentum and associated mixing in stellar interiors.  Nearly complete surveys of rotation periods are now available for star clusters and star forming regions down to much lower masses than were available before, and they are challenging our ideas about angular momentum evolution. We have strong evidence that rapid rotation in M dwarfs, traditionally attributed to weak torques, is imprinted early in their evolution, while higher mass stars are born rotating more slowly.  I will also present evidence for differences between the rotation of (non-synchronized) binary stars and single stars, and environmental effects on the distribution of stellar rotation rates.  Star spots also appear to have a significant impact on stellar structure, inducing significant changes in stellar radii.  For the Kepler field, there is evidence for both a maximum age for rotation as a population diagnostic and a possible transition in stellar dynamos below a critical rotation rate.  Older stars also appear to be able to spin down to very long rotation periods much earlier than anticipated, with a possible change in behavior near the fully convective boundary.  I will close by reviewing the massive data sets that should be available soon and the wide range of potential applications that they will have.