Magnetic activity in late-type giant stars: Numerical MHD simulations of non-linear dynamo action in Betelgeuse

Evidence is presented from numerical magneto-hydrodynamical simulations for the existence of magnetic activity in late-type giant stars. A red supergiant with stellar parameters similar to that of Betelgeuse (alpha Orionis) is modeled as a star-in-a-box with the high-order Pencil Code. Both linear kinematic and non-linear saturated dynamo action are possible: the non-linear magnetic field saturates at a super-equipartition value corresponding to surface magnetic field of field strengths up to similar to500 Gauss. In the linear regime two different modes of dynamo action are found with exponential growth rates of similar to4 and 25 years, respectively. It is speculated that magnetic activity of late-type giants may influence dust and wind formation and possibly lead to the heating of the outer atmospheres of these stars.