Rapidly rotating red giants

TL;DR

This paper presents an automated method to measure core rotation in red giants using seismic data, focusing on stars with rapid core rotation and complex spectra, to enhance understanding of stellar interior dynamics.

Contribution

The authors develop and validate a new automated technique to accurately measure core rotation in red giants, especially those with rapid rotation and complex spectra.

Findings

Method effectively measures core rotation in rapid rotators.

Identification of mode crossings improves measurement precision.

Application to Kepler and CoRoT data yields new insights into stellar core dynamics.

Abstract

Stellar oscillations give seismic information on the internal properties of stars. Red giants are targets of interest since they present mixed modes, which behave as pressure modes in the convective envelope and as gravity modes in the radiative core. Mixed modes thus directly probe red giant cores, and allow in particular the study of their mean core rotation. The high-quality data obtained by CoRoT and Kepler satellites represent an unprecedented perspective to obtain thousands of measurements of red giant core rotation, in order to improve our understanding of stellar physics in deep stellar interiors. We developed an automated method to obtain such core rotation measurements and validated it for stars on the red giant branch. In this work, we particularly focus on the specific application of this method to red giants having a rapid core rotation. They show complex spectra where it is tricky to disentangle rotational splittings from mixed-mode period spacings. We demonstrate that the method based on the identification of mode crossings is precise and efficient. The determination of the mean core rotation directly derives from the precise measurement of the asymptotic period spacing {\Delta}{\Pi}1 and of the frequency at which the crossing of the rotational components is observed.