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http://hdl.handle.net/20.500.12386/28389
Titolo: | Analytic mean-field α^2-dynamo with a force-free corona | Autori: | BONANNO, Alfio Maurizio DEL SORDO, FABIO |
Data pubblicazione: | 2017 | Rivista: | ASTRONOMY & ASTROPHYSICS | Numero: | 605 | Da pagina:: | A33 | Abstract: | 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. <BR /> Aims: We aim to analytically evaluate the effect of coronal currents and of an outer boundary condition on the efficiency of an α<SUP>2</SUP> dynamo. We intend to estimate the change in geometry and dynamo excitation numbers with respect to the current-free case. <BR /> 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 ∇ × B = βB. <BR /> Results: The dynamo number is a decreasing function of β. Moreover, if the current is parallel to the field (β > 0), the dynamo number is smaller than in the force-free case. In contrast, for (β < 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. | URI: | http://hdl.handle.net/20.500.12386/28389 | URL: | https://www.aanda.org/articles/aa/abs/2017/09/aa31330-17/aa31330-17.html | ISSN: | 0004-6361 | DOI: | 10.1051/0004-6361/201731330 | Bibcode ADS: | 2017A&A...605A..33B | Fulltext: | open |
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