Dynamo Simulations Confirm Predominantly Toroidal Fields in Near-Core Region of an Intermediate-Mass Star

Recent asteroseismic analysis of the main-sequence F star KIC 9244992 has revealed evidence for a strong, predominantly toroidal magnetic field in its deep radiative interior. Motivated by this result, we present three-dimensional anelastic magneto-hydrodynamic simulations of a rotating 2 solar mass main-sequence star to investigate whether such internal magnetic field strengths and geometries naturally arise in global stellar dynamo simulations for stars within a similar mass range. These simulations self-consistently generate magnetic fields with azimuthal components that dominate over radial components by factors of several near the peak of the Brunt-Vaisala frequency left behind as the core recedes. Moreover, these field strengths arise despite near-uniform, spherically-averaged, rotation from the near-core region to the surface. When the Reynolds number is greater than 100 and the appropriate Rossby number is used, the resulting field strengths and geometrical properties are consistent with those inferred asteroseismically for KIC 9244992. These results indicate that a dominant toroidal field in the near-core region is a generic field configuration in core-convecting stars and should be considered in future asteroseismic inferences.