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Polar spots and stellar spindown: is dynamo saturation needed?

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Abstract

Dynamo saturation is often invoked when calculating the rotational evolution of cool stars. At rapid rotation rates a saturated dynamo reduces the angular momentum carried away by the stellar wind. This, in turn, may explain the high rotation rates present in the distribution of rotation periods in young clusters. Here we point out that concentration of magnetic flux near the poles of rapidly rotating cool stars provides an alternative to dynamo saturation. A high-latitude concentration of field on rapid rotators saturates the angular momentum loss induced by the stellar wind, due to the reduced torque arm. We show that the inclusion of this effect in model calculations is able to reproduce the observed high rotation rates without the need for dynamo saturation. Taken together with the results of O'Dell et al. (1995) this argues against dynamo saturation at low rotation rates.

Year of Publication
1997
Journal
Astronomy & Astrophysics
Volume
325
Number
3
Number of Pages
1039-1044
Date Published
Sep
ISBN Number
0004-6361
PId
718494099e00e45c5ddee57b5093b1c4
Journal Article
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