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Analytic mean-field alpha(2)-dynamo with a force-free corona
INAF Osservatorio Astrofis Catania, I-95125 Catania, Italy..
KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Yale Univ, Dept Geol & Geophys, POB 6666, New Haven, CT 06511 USA.;Stockholm Univ, S-10691 Stockholm, Sweden..
2017 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 605, article id A33Article in journal (Refereed) Published
Abstract [en]

Context. Stellar dynamos are affected by boundary conditions imposed by stellar coronae. Under some approximations, it is possible to find analytical solutions. Interior dynamo models often consider a current-free corona without taking into account the constraints imposed by the presence of currents in the corona. Aims. We aim to analytically evaluate the effect of coronal currents and of an outer boundary condition on the efficiency of an alpha(2) dynamo. We intend to estimate the change in geometry and dynamo excitation numbers with respect to the current-free case. Methods. We analytically solved the turbulent dynamo induction equation for a homogeneous, non-mirror symmetric turbulence in a spherical domain surrounded by a linear force-free corona with the mean magnetic field B satisfying del x B = beta B. Results. The dynamo number is a decreasing function of beta. Moreover, if the current is parallel to the field (beta > 0), the dynamo number is smaller than in the force- free case. In contrast, for (beta < 0), the dynamo number is greater than in the force-free case. Conclusions. Currents in the corona need to be taken into account because they affect the condition for excitation of a dynamo.

Place, publisher, year, edition, pages
EDP Sciences, 2017. Vol. 605, article id A33
Keywords [en]
dynamo, stars: coronae, stars: magnetic field
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-243503DOI: 10.1051/0004-6361/201731330ISI: 000412231200099Scopus ID: 2-s2.0-85028914380OAI: oai:DiVA.org:kth-243503DiVA, id: diva2:1287390
Note

QC 20190211

Available from: 2019-02-11 Created: 2019-02-11 Last updated: 2019-02-11Bibliographically approved

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