Migrating Dynamo Waves and Consequences for Stellar Current Sheets

Abstract

We study the relation between stellar dynamo-wave propagation and the structure of the stellar magnetic field. Modeling dynamo waves by the well-known Parker migratory dynamo, we vary the intensity of dynamo drivers in order to obtain activity-wave propagation toward the Equator (as in the solar-activity cycle) or towards the Poles. We match the magnetic field in the dynamo-active shell with that in the surrounding stellar material, using a simple dissipative magneto-hydrodynamic system for the transition region. Introducing a weak asymmetry between the stellar hemispheres, we study phase shifts of the dipole, quadrupole, and octupole magnetic components at various distances from the star to demonstrate that a several-percent asymmetry in dynamo drivers is sufficient to obtain a realistic relation between solar dipole and quadrupole moments. We study the behavior of the stellar current sheets and show that for the poleward-propagating activity it is substantially different from solar ones. In particular, we demonstrate conditions in which the conical current sheets propagate opposite to the solar directions.