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Anharmonic and Standing Dynamo Waves: Theory and Observation of Stellar Magnetic Activity

机译:非谐波和常驻发电波:恒星磁活动的理论与观测

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The familiar decadal cycle of solar activity is one expression of interannual variability of surface magnetism observed in stars on or near the lower main sequence. Records of Ca II H and K fluxes obtained for such stars by Mount Wilson Observatory's HK Project extend back over 35 years. From these records, we define a new measure of anharmonicity that connects to the 2-D description of a Parker dynamo model. We explore the parameter space of this model and find an excellent counterpart to solutions containing highly anharmonic, standing dynamo waves in the records of several of the lowest mass (late K- to early M-type) active stars in the sample. We interpret anharmonicity as resulting from non-propagating or standing dynamo waves, which operate in a substantially supercritical regime. There, for most of the cycle, large-scale magnetic fields are generated and maintained by winding of field by differential rotation rather than by joint action of differential rotation and helical convection. Further, less active stars like the Sun show simple harmonic, migratory and/or intermediate-type dynamo wave patterns over a broad range of dynamo parameters.

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