Constraining the core-rotation rate in red-giant stars from Kepler space photometry

TL;DR

This study uses Kepler space photometry to analyze rotational splitting in red giant stars, providing new constraints on their internal rotation profiles and advancing understanding of stellar evolution.

Contribution

It presents the first large sample analysis of dipole mode splitting in red giants, constraining core-to-surface rotation rates through asteroseismology.

Findings

Core-to-surface rotation rate constraints for evolved stars

Detection of rotational splitting in individual dipole modes

Insights into internal stellar rotation dynamics

Abstract

Rotation plays a key role in stellar structure and its evolution. Through transport processes which induce rotational mixing of chemical species and the redistribution of angular momentum, internal stellar rotation influences the evolutionary tracks in the Hertzsprung-Russell diagram. In turn, evolution influences the rotational properties. Therefore, information on the rotational properties of the deep interior would help to better understand the stellar evolution. However, as the internal rotational profile cannot be measured directly, it remains a major unknown leaving this important aspect of models unconstrained. We can test for nonrigid rotation inside the stars with asteroseismology. Through the effect of rotational splitting of non-radial oscillation modes, we investigate the internal rotation profile indirectly. Red giants have very slow rotation rates leading to a rotational splitting on the level of a few tenth of a \mu Hz. Only from more than 1.5 years of consecutive data from the NASA Kepler space telescope, these tiny variations could be resolved. A qualitative comparison to theoretical models allowed constraining the core-to-surface rotation rate for some of these evolved stars. In this paper, we report on the first results of a large sample study of splitting of individual dipole modes.