Starspots as tracers of differential surface rotation

Abstract

Differential rotation is a key ingredient in theories of stellar magnetic field generation. The solar surface differential rotation was initially discovered via the simple method of tracking the rotation rates of individual starspots at different latitudes. Today, the same technique can be applied to rapidly rotating stars, using sequences of Doppler images spanning several stellar rotations. Early results suggest that solar-like differential rotation patterns prevail on rapidly rotating dwarf stars, but much remains to be done in tracing global flow patterns on pre-main sequence stars, giants, and tidally-locked binary components. I outline the relative merits of the three main methods that have so far been used to track the latitude dependence of starspot rotation rates, and discuss the validity of the physical assumptions that underpin them.