Solar and Stellar Magnetic Activity, CAPS
- C. Schrijver, C. Zwaan
Betelgeuse is an example of a nearby cool super-giant that displays temporal brightness fluctuations and irregular surface structures. Recent numerical simulations by Freytag and collaborators of the outer convective envelope comprising most of the entire star under realistic physical assumptions, have shown that the fluctuations in the star’s apparent luminosity may be caused by giant cell convection, very dissimilar to solar convection. These detailed simulations bring forth the possibility of addressing another question regarding the nature of Betelgeuse and super-giants in general; namely whether these stars may harbor magnetic activity, which may contribute to their variability. Taking the detailed numerical simulations of the star at face value, we have applied a kinematic dynamo analysis to study whether or not the flow field of this super-giant may be able to amplify a weak seed magnetic field. We find that the giant cell convection does indeed allow a positive exponential growth rate of magnetic energy. The possible Betelgeusian dynamo can be characterized as belonging to the class of so-called “local small-scale dynamos” another often mentioned example of which is the dynamo action in the solar photosphere that may be responsible for the formation of small-scale flux tubes (magnetic bright points). However, in the case of Betelgeuse this designation is less meaningful since the generated magnetic field is both global and large-scale.