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Paper: Rotation and the Circumstellar Environment (Invited Review)
Volume: 361, Active OB-Stars: Laboratories For Stellar and Circumstellar Physics
Page: 15
Authors: Howarth, I.D.
Abstract: The observational effects of rotation on outflows in OB stars are reviewed. Direct evidence of global asymmetries in outflows resulting from moderate rotation are subtle and ambiguous. ‘Discrete absorption components’ have been suggested as indicators of time-dependent rotational modulation, and recurrence timescales do correlate, loosely, with the line-width parameter v sin i, but the underlying mechanism remains elusive; neither magnetic fields nor pulsations offer a satisfactory framework for the interpretation of these episodic features. However, where truly periodic signals are observed in hot-star winds, they are associated with strong magnetic fields; new results on two early-type stars illustrate this. Finally, the role of rapid (near-critical) rotation in Be stars is examined. A simple statistical analysis is used to argue that the observed distribution of v sin i values is consistent with Be stars rotating at ∼95% of critical, which allows ‘weak’ processes (operating at or near the sound speed) to play a significant role in the production of keplerian viscous decretion disks.
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