Large-scale measurements of the red giant core rotation through asteroseismology

TL;DR

This study uses a new automated asteroseismic method to measure core rotation in nearly 1200 red giants, revealing slower core braking than previously thought and no dependence on stellar mass.

Contribution

An automated technique for measuring red giant core rotation from Kepler data, enabling large-scale analysis and future application to PLATO data.

Findings

Core rotation braking rate is lower than earlier estimates.

Core rotation rate does not depend on stellar mass.

Method can analyze hundreds of thousands of spectra.

Abstract

Red giant stars are solar-like pulsators presenting mixed-modes. Such modes consist in a coupling between pressure waves propagating in the external convective envelope and gravity waves propagating in the radiative interior. Therefore, the red giant asteroseismology provides us with a direct view on their core and opens the possibility to monitor the evolution of their core rotation. Previous measurements of the mean core rotation revealed that angular momentum is efficiently transferred from the core to the envelope inside red giants, but the physical mechanisms at work are not yet fully understood. We thus need stronger observational constraints on the evolution of the red giant core rotation. In this context, we developed an automated method to determine the mean core rotation of red giant branch stars observed with Kepler. This automated method is paving the way for the future PLATO data, representing hundreds of thousands of potential red giant oscillation spectra. Results obtained for almost 1200 red giant branch stars indicate that the rate of the core rotation braking is lower than previously estimated and does not seem to depend on the stellar mass.