Dynamos with a flat α-effect distribution |
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Authors: | A Brandenburg I Tuominen F Krause |
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Institution: | 1. Observatory and Astrophysics Laboratory , University of Helsinki , T?htitorninm?ki, SF-00131, Helsinki, Finland;2. Sternwarte Babelsberg, Akademie der Wissenschaften der DDR , Rosa-Luxemburg-Str. 17a, Potsdam, German Democratic Republic , 1591 |
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Abstract: | Abstract In order to obtain a better insight into the excitation conditions of magnetic fields in flat objects, such as galaxies, we have calculated critical dynamo numbers of different magnetic field modes for spherical dynamos with a flat α-effect distribution. A simple but realistic approximation formula for the rotation curve is employed. In most cases investigated a stationary quadrupole-type solution is preferred. This is a consequence of the flat distribution of the α-effect. Non-axisymmetric fields are in all cases harder to excite than axisymmetric ones. This seems to be the case particularly for flat objects in combination with a realistic rotation curve for galaxies. The question of whether non-axisymmetric (bisymmetric) fields, which are observed in some galaxies, can be explained as dynamos generated by an axisymmetric αω-effect is therefore still open. |
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Keywords: | α-effect dynamo action galactic dynamos |
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