Journal Article

A semi-analytic approach to angular momentum transport in stellar radiative interiors

F. Spada, A. C. Lanzafame and A. F. Lanza

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 404, issue 2, pages 641-660
Published in print May 2010 | ISSN: 0035-8711
Published online May 2010 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2010.16325.x
A semi-analytic approach to angular momentum transport in stellar radiative interiors

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We address the problem of angular momentum transport in stellar radiative interiors with a novel semi-analytic spectral technique, using an eigenfunction series expansion, that can be used to derive benchmark solutions in hydromagnetic regimes with very high Reynolds number (107–108). The error arising from the truncation of the series is evaluated analytically. The main simplifying assumptions are the neglect of meridional circulation and of non-axisymmetric magnetic fields. The advantages of our approach are shown by applying it to a spin-down model for a 1 M main-sequence star. The evolution of the coupling between core and envelope is investigated for different values of the viscosity and different geometries and values of the poloidal field. We confirm that a viscosity enhancement by ∼104 with respect to the molecular value is required to attain a rigid rotation in the core of the Sun within its present age. We suggest that a quadrupolar poloidal field may explain the short coupling time-scale needed to model the observed rotational evolution of fast rotators on the zero-age main-sequence, while a dipolar geometry is indicated in the case of slow rotators. Our novel semi-analytic spectral method provides a conceptually simple and rigorous treatment of a classic magnetohydrodynamic problem and allows us to explore the influence of various parameters on the rotational history of radiative interiors.

Keywords: MHD; methods: analytical; methods: numerical; stars: late-type; stars: magnetic fields; stars: rotation

Journal Article.  10912 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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