Differential rotation in K, G, F and A stars

TL;DR

This study measures and analyzes the differential rotation in K, G, F, and A stars using Kepler data, revealing how shear varies with temperature and rotation rate, and comparing observations with theoretical models.

Contribution

It provides the first comprehensive measurement of rotational shear across a wide range of stellar types and compares these with theoretical predictions.

Findings

Shear peaks in F stars and decreases in A stars.

Weak shear dependence on rotation rate in K and G stars.

Strong increase in stars with zero frequency spread at higher temperatures.

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. The variation of rotational shear as a function of effective temperature in restricted ranges of rotation period is determined. The shear increases to a maximum in F stars, but decreases somewhat in the A stars. Theoretical models reproduce the temperature variation quite well. The dependence of rotation shear on rotation rate in restricted temperature ranges is also determined. 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. There is a strong increase in the fraction of stars with zero frequency spread with increasing effective temperature. The time-frequency diagrams for A stars are no different from those in cool stars, further supporting the presence of spots in stars with radiative envelopes.