July 11-15, 2011
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What Sets the Rotation Rates of Massive Stars?

Anna Rosen (UC Santa Cruz)

Rosen A.L., Krumholz M.R., Ramirez-Ruiz E. (Department of Astronomy, University of California, Santa Cruz, CA 95064, US)

The physical mechanisms that set the initial rotation rates in massive stars are a crucial unknown in current star formation theory. Observations of young, massive stars provide evidence that they form in a similar fashion to their low-mass counterparts. It has been shown that the magnetic coupling between the star and its accretion disk is sufficient to spin down low-mass PMS stars to below breakup at the end stage of their formation when the accretion rate is low. However, we find that these magnetic torques are insufficient to spin down massive PMS stars due to their short formation times and high accretion rates. To explore this issue we model the angular momentum evolution for a wide range of stellar masses by considering both magnetic and gravitational torques. We explore the regimes in which each mechanism dominates in regulating the stellar rotation rate, and predict the mass dependence of the initial rotation rates of stars.

Mode of presentation: poster