Dynamo cycles in global convection simulations of solar-like stars

Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
e-mail: warnecke@mps.mpg.de

Received: 4 December 2017
Accepted: 25 April 2018

Abstract

Context. Several solar-like stars exhibit cyclic magnetic activity similar to the Sun as found in photospheric and chromospheric emission.

Aims. We seek to understand the physical mechanism involved in rotational dependence of these activity cycle periods.

Methods. We used three-dimensional magnetohydrodynamical simulations of global convective dynamos models of solar-like stars to investigate the rotational dependency of dynamos. We further applied the test-field method to determine the α effect in these simulations.

Results. We find dynamos with clear oscillating mean magnetic fields for moderately and rapidly rotating runs. For slower rotation, the field is constant or exhibit irregular cycles. In the moderately and rapidly rotating regime the cycle periods increase weakly with rotation. This behavior can be well explained with a Parker–Yoshimura dynamo wave traveling equatorward. Even though the α effect becomes stronger for increasing rotation, the shear decreases more steeply, causing this weak dependence on rotation. Similar to other numerical studies, we find no indication of activity branches that have been postulated in former observational studies. However, our simulations seem to agree more with the transitional branch suggested by more recent observational studies. If the Sun exhibited a dynamo wave similar to that which we find in our simulations, it would operate deep inside the convection zone.