Powering Stellar Magnetism: Energy Transfers in Cyclic Dynamos of Sun-like Stars

We use the anelastic spherical harmonic code to model the convective dynamo of solar-type stars. Based on a series of 15 3D MHD simulations spanning four bins in rotation and mass, we show what mechanisms are at work in these stellar dynamos with and without magnetic cycles and how global stellar parameters affect the outcome. We also derive scaling laws for the differential rotation and magnetic field based on these simulations. We find a weaker trend between differential rotation and stellar rotation rate, (Delta Omega proportional to (vertical bar Omega vertical bar/Omega(circle dot))(0.46)) in the MHD solutions than in their HD counterpart (vertical bar Omega vertical bar/Omega(circle dot))(0.66)) yielding a better agreement with the observational trends based on power laws. We find that for a fluid Rossby number between 0.15 less than or similar to ROf less than or similar to 0.65, the solutions possess long magnetic cycle, if ROf less than or similar to 0.42 a short cycle and if ROf greater than or similar to 1 (antisolar-like differential rotation), a statistically steady state. We show that short-cycle dynamos follow the classical Parker-Yoshimura rule whereas the long-cycle period ones do not. We also find efficient energy transfer between reservoirs, leading to the conversion of several percent of the star's luminosity into magnetic energy that could provide enough free energy to sustain intense eruptive behavior at the star's surface. We further demonstrate that the Rossby number dependency of the large-scale surface magnetic field in the simulation (B-L,B-surf similar to ROf (-1.)(26)) agrees better with observations (B-V similar to ROs-1.4 +/- 0.1) and differs from dynamo scaling based on the global magnetic energy (B-bulk similar to ROf-0.5).