Detection of differential rotation inψCap with profile analysis

We report detection of differential rotation on the F5 dwarf ψ Cap using line profile analysis. The Fourier transform of both Fe i λ5775 and Si i λ5772 are used to obtain a projected rotational velocity of $v \sin{i}=42\pm1$ km s-1. Modelling of the Fourier transformed profiles shows that the combined effects of equatorial velocity, inclination and differential rotation dominate the line profile while limb darkening and turbulence velocities have only minor effects. Rigid rotation is shown to be inconsistent with the measured profiles. Modelling the line profiles analogous to solar differential rotation we find a differential rotation parameter of $\alpha=0.15\pm0.1$ ($15\pm10$% ) comparable to the solar case. To our knowledge this is the first successful measurement of differential rotation through line profile analysis.