Differential rotation in K, G, F and A stars

Abstract

Rotational light modulation in Kepler photometry of K-A stars is used to estimate the absolute rotational shear. The rotation frequency spread in 2562 carefully selected stars with known rotation periods is measured using time-frequency diagrams. Because rotational shear is both a function of effective temperature and rotation rate, it is necessary to separate the two effects by calculating the rotation shear in restricted ranges of effective temperature and rotation period. The shear increases to a maximum in F stars, but decreases somewhat in the A stars. Theoretical models reproduce the variation of rotational shear with effective temperature quite well for all rotation rates. The dependence of the shear on the rotation rate is weak in K and G stars, increases rapidly for F stars and is strongest in A stars. For stars earlier than type K, a discrepancy exists between the predicted and observed variation of shear with rotation rate.