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(Reference retrieved automatically from Web of Science through information on FAPESP grant and its corresponding number as mentioned in the publication by the authors.)

What Sets the Magnetic Field Strength and Cycle Period in Solar-type Stars?

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Author(s):
Guerrero, G. [1] ; Zaire, B. [1, 2] ; Smolarkiewicz, P. K. [3] ; de Gouveia Dal Pino, E. M. [4] ; Kosovichev, A. G. [5] ; Mansour, N. N. [6]
Total Authors: 6
Affiliation:
[1] Univ Fed Minas Gerais, Phys Dept, Av Antonio Carlos 6627, BR-31270901 Belo Horizonte, MG - Brazil
[2] Univ Toulouse, UPS, CNES, IRAP, CNRS UMR 5277, 14 Ave E Belin, F-31400 Toulouse - France
[3] European Ctr Medium Range Weather Forecasts, Reading RG2 9AX, Berks - England
[4] Univ Sao Paulo, Astron Dept, IAG USP, Rua Matao 1226, BR-05508090 Sao Paulo, SP - Brazil
[5] New Jersey Inst Technol, Newark, NJ 07103 - USA
[6] NASA, Ames Res Ctr, Mountain View, CA 94040 - USA
Total Affiliations: 6
Document type: Journal article
Source: ASTROPHYSICAL JOURNAL; v. 880, n. 1 JUL 20 2019.
Web of Science Citations: 2
Abstract

Two fundamental properties of stellar magnetic fields have been determined by observations for solar-like stars with different Rossby numbers (Ro), namely, the magnetic field strength and the magnetic cycle period. The field strength exhibits two regimes: (1) for fast rotation, it is independent of Ro, and (2) for slow rotation, it decays with Ro following a power law. For the magnetic cycle period, two regimes of activity, the active and inactive branches, have also been identified. For both of them, the longer the rotation period, the longer the activity cycle. Using global dynamo simulations of solar-like stars with Rossby numbers between similar to 0.4 and similar to 2, this paper explores the relevance of rotational shear layers in determining these observational properties. Our results, consistent with nonlinear alpha(2)Omega dynamos, show that the total magnetic field strength is independent of the rotation period. Yet at surface levels, the origin of the magnetic field is determined by Ro. While for Ro less than or similar to 1, it is generated in the convection zone, for Ro greater than or similar to 1, strong toroidal fields are generated at the tachocline and rapidly emerge toward the surface. In agreement with the observations, the magnetic cycle period increases with the rotational period. However, a bifurcation is observed for Ro similar to 1, separating a regime where oscillatory dynamos operate mainly in the convection zone from the regime where the tachocline has a predominant role. In the latter, the cycles are believed to result from the periodic energy exchange between the dynamo and the magneto-shear instabilities developing in the tachocline and the radiative interior. (AU)

FAPESP's process: 13/10559-5 - Investigation of high energy and plasma astrophysics phenomena: theory, numerical simulations, observations, and instrument development for the Cherenkov Telescope Array (CTA)
Grantee:Elisabete Maria de Gouveia Dal Pino
Support type: Research Projects - Thematic Grants