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Paper: Evolution of Rotation Rates in Massive Stars: Effects of Binarity and Low Metallicity
Volume: 367, Massive Stars in Interactive Binaries
Page: 101
Authors: Penny, L.R.
Abstract: We examine the separate effects of binary membership and low metallicity on the rotation rates of evolved massive stars. Past observations of single stars at Galactic metallicities show that these stars slow down in rotational velocity as they evolve on the Main Sequence. However for members of close binary systems, the dominant effect upon their rotation rates is the synchronization of their spin velocity to their orbital velocity. New NLTE stellar interior models assume an evolution of angular momentum loss for single stars. We caution the use of these models as comparison for members of close binaries based on the differing evolution of angular momentum loss. Recent theoretical predictions for low metallicity massive stars predict that these stars should have drastically reduced equatorial winds (mass loss) while on the main sequence, and as such should retain most of their angular momentum. We present V sin i values for 21 Large Magellanic Cloud and 22 Small Magellanic Cloud O-type stars based on STIS and IUE UV spectroscopy. Despite the theoretical predictions and indirect observational evidence for high rotation, the O type stars in the Magellanic Clouds do not appear to rotate faster than their Galactic counterparts.
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