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Paper: What Sets the Rotation Rates of Massive Stars?
Volume: 465, Four Decades of Massive Star Research - A Scientific Meeting in Honor of Anthony J. Moffat
Page: 98
Authors: Rosen, A. L.; Krumholz, M. R.; Ramirez-Ruiz, E.
Abstract: The physical mechanisms that set the initial rotation rates in massive stars are a crucial unknown in current star formation theory. It has been shown that the magnetic coupling between the star and its accretion disk is sufficient to spin down low-mass pre-main sequence (PMS) stars to well 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 find that magnetic torques are unable to spin down either low or high mass stars during the main accretion phase, and that massive stars cannot be spun down significantly by magnetic torques during the end stage of their formation either. Spin-down occurs only if massive stars' disk lifetimes are substantially longer or their magnetic fields are much stronger than current observations suggest.
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