Journal Article

Modelling the rotational evolution of solar-like stars: the rotational coupling time-scale

F. Spada, A. C. Lanzafame, A. F. Lanza, S. Messina and A. Collier Cameron

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 416, issue 1, pages 447-456
Published in print September 2011 | ISSN: 0035-8711
Published online August 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2011.19052.x
Modelling the rotational evolution of solar-like stars: the rotational coupling time-scale

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We investigate the rotational evolution of solar-like stars with a focus on the internal angular momentum transport processes. The double-zone model, in which the star’s radiative core and convective envelope are assumed to rotate as solid bodies, is used to test simple relationships between the core–envelope coupling time-scale, τc, and rotational properties, like the envelope angular velocity or the differential rotation at the core–envelope interface. The trial relationships are tested by fitting the model parameters to available observations via a Markov chain Monte Carlo method. The synthetic distributions are tested for compatibility with their observational counterparts by means of the standard Kolmogorov–Smirnov (KS) test.

A power-law dependence of τc on the inner differential rotation leads to a more satisfactory agreement with observations than a two-valued prescription for τc, which would imply a dichotomy between the initially slow (Prot≳ 3 d) and fast (Prot≲ 3 d) rotators. However, we find it impossible to reconcile the high fraction of fast rotators in α Per with the rotation period distributions in stellar systems at earlier and later evolutionary stages. This could be explained by local environmental effects (e.g. early removal of circumstellar discs due to ultraviolet radiation and winds from nearby high-mass stars) or by observational biases.

The low KS probability that the synthetic and observed distributions are not incompatible, found in some cases, may be due to oversimplified assumptions of the double-zone model, but the large relative uncertainties in the age determination of very young clusters and associations are expected to play a relevant role. Other possible limitations and uncertainties are discussed.

Keywords: methods: numerical; stars: interiors; stars: late-type; stars: pre-main-sequence; stars: rotation

Journal Article.  7352 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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