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The spin-up of contracting red supergiants
A. Heger 1 and
N. Langer 2
Received 15 January 1998 / Accepted 17 February 1998
We report on a mechanism which may lead to a spin-up of the surface of a rotating single star leaving the Hayashi line, which is much stronger than the spin-up expected from the mere contraction of the star.
By analyzing rigidly rotating, convective stellar envelopes, we qualitatively work out the mechanism through which these envelopes may be spun up or down by mass loss through their lower or upper boundary, respectively. We find that the first case describes the situation in retreating convective envelopes, which tend to retain most of the angular momentum while becoming less massive, thereby increasing the specific angular momentum in the convection zone and thus in the layers close to the stellar surface. We explore the spin-up mechanism quantitatively in a stellar evolution calculation of a rotating star, which is found to be spun up to critical rotation after leaving the red supergiant branch.
We discuss implications of this spin-up for the circumstellar matter around several types of stars, i.e., post-AGB stars, B[e] stars, pre-main sequence stars, and, in particular, the progenitor of Supernova 1987A.
Key words: stars: evolution stars: rotation circumstellar matter stars: supergiants supernovae: individual: SN 1987A
Send offprint requests to: A. Heger
© European Southern Observatory (ESO) 1998
Online publication: May 12, 1998