Understanding angular momentum transport in red giants: the case of KIC 7341231

TL;DR

This study models the internal rotation profile of the red giant KIC 7341231 to identify the physical mechanisms responsible for angular momentum transport, emphasizing the need for an additional efficient process beyond meridional circulation and shear mixing.

Contribution

It demonstrates that standard rotational mixing processes are insufficient and highlights the importance of an extra angular momentum transport mechanism active throughout stellar evolution.

Findings

Standard processes produce too steep a rotation profile.

An additional mechanism is required for accurate modeling.

Whole stellar rotational history influences current rotation profiles.

Abstract

Context. Thanks to recent asteroseismic observations, it has been possible to infer the radial differential rotation profile of subgiants and red giants. Aims. We want to reproduce through modeling the observed rotation profile of the early red giant KIC 7341231 and constrain the physical mechanisms responsible for angular momentum transport in stellar interiors. Methods. We compute models of KIC 7341231 including a treatment of shellular rotation and we compare the rotation profiles obtained with the one derived by Deheuvels et al. (2012). We then modify some modeling parameters in order to quantify their effect on the obtained rotation profile. Moreover, we mimic a powerful angular momentum transport during the Main Sequence and study its effect on the evolution of the rotation profile during the subgiant and red giant phases. Results. We show that meridional circulation and shear mixing alone produce a rotation profile for KIC 7341231 too steep compared to the observed one. An additional mechanism is then needed to increase the internal transport of angular momentum. We find that this undetermined mechanism has to be efficient not only during the Main Sequence but also during the much quicker subgiant phase. Moreover, we point out the importance of studying the whole rotational history of a star in order to explain its rotation profile during the red giant evolution.