Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006mnras.373..819l&link_type=abstract
Monthly Notices of the Royal Astronomical Society, Volume 373, Issue 2, pp. 819-826.
Astronomy and Astrophysics
Astronomy
9
Stars: Activity, Stars: Individual: Ab Dor, Stars: Individual: Lq Hya, Stars: Late-Type, Stars: Magnetic Fields, Stars: Rotation
Scientific paper
A model for the angular momentum transfer within the convection zone of a rapidly rotating star is introduced and applied to the analysis of recent observations of temporal fluctuations of the differential rotation on the young late-type stars AB Doradus (AB Dor) and LQ Hydrae (LQ Hya). Under the hypothesis that the mean magnetic field produced by the stellar dynamo rules the angular momentum exchanges and that the angular velocity depends only on the distance s from the rotation axis and the time, the minimum azimuthal Maxwell stress |BsBϕ|, averaged over the convection zone, is found to range from ~0.04 to ~0.14T2. If the poloidal mean magnetic field Bs is of the order of 0.01T, as indicated by the Zeeman-Doppler imaging maps of those stars, then the azimuthal mean field Bϕ can reach an intensity of several teslas, which significantly exceeds equipartition with the turbulent kinetic energy. Such strong fields can account also for the orbital period modulation observed in cataclysmic variables and RS Canum Venaticorum systems with a main-sequence secondary component. Moreover, the model allows us to compute the kinetic energy dissipation rate during the maintenance of the differential rotation. Only in the case of the largest surface shear observed on LQ Hya may the dissipated power exceed the stellar luminosity, but the lack of a sufficient statistic on the occurrence of such episodes of large shear does not allow us to estimate their impact on the energy budget of the convection zone.
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