Modelling differential rotation of red giants: the case of the evolved sun

TL;DR

This study models the differential rotation in red giants, explaining the faster core rotation through angular momentum transport theory, aligning with asteroseismic observations of core-envelope rotational differences.

Contribution

It introduces a differential rotation model based on angular momentum transport theory applied to red giants, explaining core-envelope rotation contrasts observed in asteroseismology.

Findings

Core rotates about ten times faster than the surface.

The rotational contrast increases with stellar age.

Model reproduces observed core spindown scaling.

Abstract

Asteroseismology has revealed that cores of red giants rotate about one order of magnitude faster than their convective envelopes. This paper attempts an explanation for this rotational state in terms of the theory of angular momentum transport in stellar convection zones. A differential rotation model based on the theory is applied to a sequence of evolutionary states of a red giant of one solar mass. The model computations show a rotation of about ten times faster in the cores compared to the stellar surface. This rotational state is caused by the non-diffusive downward convective transport of angular momentum. The contrast in rotational rates between core and envelope increases with the radius (age) of the star. Seismologically detected scaling for the spindown of the giants' cores is also reproduced.