Differential Rotation in Sun-like Stars from Surface Variability and Asteroseismology

Abstract

Thanks to helioseismology we know the internal rotation of the Sun as a function of radius and latitude. The presence of a shear at the base of the solar convection zone is thought to play a key role in the generation of magnetic fields. So far however, the internal rotation profiles of stars other than the Sun are unknown, and placing constraints on models of rotation and magnetic dynamos is therefore difficult.. The NASA Kepler mission has provided high-quality photometric data that can be used to study the rotation of stars with two different techniques; asteroseismology and surface activity. First, we developed an automated method for measuring the rotation of stars using surface variability. This was initially applied to 12 000 stars across the main sequence in the Kepler field, providing robust estimates of the surface rotation rates and the associated errors. We compared these measurements to spectroscopic vsin(i) values and found good agreement for F-,G- and K-type stars. Second, we performed an asteroseismic analysis of six Sun-like stars, where we were able to measure the rotational splitting as a function of frequency in the p-mode envelope. The measured splittings were all consistent with a constant value, indicating little differential rotation. Third, we compared the asteroseismic rotation rates of five Sun-like stars to their surface rotation rates. We found that the values were in good agreement, indicating little differential rotation between the regions where the two methods are most sensitive. Finally, we discuss how the surface rotation rates may be used as a prior on the seismic envelope rotation rate, allowing us to find upper limits on the radial differential rotation in Sun-like stars. We find that the rotation rates of the radiative interior and convective envelope likely do not di er by more than 50%.