Third BCool Meeting

According to dynamo models, the variable magnetic field of the Sun is the consequence of the interplay between two main ingredients. The first ingredient is the radial and latitudinal differential rotation that succeeds at generating a large-scale toroidal magnetic field from an initial poloidal field. The second ingredient is still a matter of debate, with models invoking either the cyclonic convection in the convection zone or the transport of decaying active regions by meridional circulation as possible processes to regenerate the poloidal magnetic component. When acting together, both effects succeed at building continuously a large-scale magnetic field that oscillates with time, giving rise to the 22 yr period of the solar cycle. Despite considerable progress in this field since the very first solar dynamo models, there are still many aspects of solar magnetism that the current models cannot reproduce or did not thoroughly explore.

Our understanding of the solar dynamo can benefit from the observation of solar-type stars, where dynamo types marginal or inactive in the Sun can be observed, either because these analogues of the Sun are caught by chance in an unfrequented activity state (similar, e.g., to the Maunder minimum) or because their physical properties (in particular their mass and rotation rate) differ sufficiently from the Sun’s to lead to a different dynamo output. Using spectropolarimetric observations, the magnetic fields of cool stars can now be directly characterized from the polarized signatures they produce in spectral lines, and the associated field geometries can be reconstructed using tomographic imaging techniques, like Zeeman-Doppler-Imaging.

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