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 found: the non-linear magnetic field saturates at a super-equipartition value (a factor two above equipartition yielding surface fields with strengths on the order of 500 Gauss), while in the linear regime two different modes of dynamo action are found. 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.