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A nonlinear model for rotating cool stars

Published online by Cambridge University Press:  26 August 2011

Sydney A. Barnes
Sydney A. Barnes*
Affiliation:
Lowell Observatory, 1400 W. Mars Hill Road, Flagstaff, AZ 86001, USA email: barnes@lowell.edu
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Abstract

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A simple nonlinear model is introduced here to describe the rotational evolution of main sequence cool (FGKM) stars. It is formulated only in terms of the ratio of a star's rotation period, P, to its convective turnover timescale, τ, and two dimensionless constants which are specified using solar- and open cluster data. The model explains the origin of the two sequences, C/fast and I/slow, of rotating stars observed in open cluster color-period diagrams, and describes their evolution from C-type to I-type through the rotational gap, g, separating them. It explains why intermediate-mass open cluster stars have the longest periods, while higher- and lower-mass cool stars have shorter periods. It provides an exact expression for the age of a rotating cool star in terms of P and τ, thereby generalizing gyrochronology. The possible range of initial periods is shown to contribute upto 128 Myr to the gyro age errors of solar mass field stars. A transformation to color-period space shows how this model explains some detailed features in the color-period diagrams of open clusters, including the shapes and widths of the sequences, and the observed number density of stars across these diagrams.

Keywords

Convection, methods: analyticalstars: evolutionstars: late-typestars: rotation
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 6 , Symposium S273: The Physics of Sun and Star Spots , August 2010 , pp. 465 - 468
Copyright
Copyright © International Astronomical Union 2011

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