The decrease in differential rotation with decreasing stellar mass in a sample of young rapidly rotating main sequence stars

Abstract

In the Sun, global fluid circulation generates the large-scale magnetic field through cyclic dynamo action. Shear at the solar core/convection zone interface ensures that the convection zone does not rotate as a solid body. At the solar surface, this leads to the equatorial regions completing one more rotation than the polar regions every similar to 120 d. Similar surface rotation patterns axe observable on other stars, allowing us to determine how the fluid circulation patterns that drive their dynamos depend on fundamental stellar parameters such as mass, age and rotation rate. Here we present measurements for the differential rotation in an homogeneous sample of young, rapidly-rotating single G2V to M2V stars. By using Doppler imaging to measure the dependence of starspot rotation rates as a function of latitude, we find that the magnitude of the surface differential rotation shear decreases with decreasing effective temperature. The implied approach to solid body rotation with increasing relative convection zone depth implies that the dynamo mechanism operating in low-mass stars may be substantially different from that in the Sun.