Dynamo action and the period gap in cataclysmic variables |
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Authors: | A. F. Lanza,M. Rodonò , R. Rosner |
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Affiliation: | Osservatorio Astrofisico di Catania, CittàUniversitaria, Viale A. Doria 6, I-95125 Catania, Italy; Department of Astronomy &Astrophysics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637, USA; Istituto di Astronomia, Universitàdegli Studi di Catania, Viale A. Doria 6, I-95125 Catania, Italy |
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Abstract: | The conjecture is presented that the gap in the distribution of the orbital periods of cataclysmic variables is related to a particular kind of hydromagnetic dynamo, called an interface dynamo, operating near the base of the convective envelope of their secondary components. Such a dynamo is characterized by the spatial separation of the regions where differential rotation and the α effect operate. Unlike conventional dynamos, the linear growth rate of an interface dynamo becomes negative for highly supercritical dynamo numbers, leading to the disappearance of the dynamo action. If such a result, from linear theory, is confirmed by non-linear calculations, it may provide a physical basis for the so-called disrupted magnetic braking hypothesis, invoked to explain the existence of the period gap by several evolutionary models of cataclysmic variables. |
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Keywords: | magnetic fields MHD stars: activity stars: magnetic fields novae, cataclysmic variables |
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