The dependence of differential rotation on temperature and rotation

Abstract

We use Doppler imaging techniques to determine the dependence of starspot rotation rates on latitude in an homogeneous sample of young, rapidly rotating solar analogues. A solar-like differential rotation law is used, where the rotation depends on sin2θ, where θ is the stellar latitude. By including this term in the image reconstruction process, using starspots as tracers, we are able to determine the magnitude of the shear over more than one rotation cycle. We also consider results from matched filter starspot tracking techniques, where individual starspot rotation rates are determined. In addition we have re-analysed published results and present a new measurement for the K3 dwarf Speedy Mic.

A total of 10 stars of spectral type G2–M2 are considered. We find a trend towards decreasing surface differential rotation 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.