Across the Tachocline Divide: Convection and Dynamo Action in M-Dwarf Stars

Abstract: The onset of the vigorous magnetic activity which characterizes the M-dwarfs coincides with a transition to fully spherical convection and consequently the loss of the tachocline—a shear layer with considerable importance for the solar dynamo. We report on a series of more than 80 massively parallel, fully 3D global MHD convection simulations used to study the dynamo action of M-dwarfs on either side of this transition. We observe a great diversity of potential magnetic behaviors, highlights from which we present here. We observe an abundance of single hemisphere dynamo states, strong magnetic interactions between travelling nests of modulated convection, self-consistent buoyant magnetic flux ropes, and major differences in the projected spin-down for stars on either side of the Tachocline Divide.