Asteroseismology of evolved stars to constrain the internal transport of angular momentum. VI. Testing a parametric formulation for the azimuthal magneto-rotational instability

TL;DR

This study tests a parametric model of the azimuthal magneto-rotational instability (AMRI) to explain the internal angular momentum transport in evolved stars, aligning stellar evolution models with asteroseismic observations of core rotation rates.

Contribution

It introduces and evaluates a parametric formulation of AMRI as a candidate mechanism for angular momentum transport in evolved stars, matching observational constraints.

Findings

The AMRI-based model reproduces core rotation rates in red giants and core-helium burning stars.

The efficiency of AMRI correlates with the differential rotation within radiative zones.

Current asteroseismic data support AMRI as a plausible process for angular momentum redistribution.

Abstract

Asteroseismic measurements of the internal rotation rate in evolved stars pointed out to a lack of angular momentum (AM) transport in stellar evolution models. Several physical processes in addition to hydrodynamical ones were proposed as candidates for the missing mechanism. Nonetheless, no current candidate can satisfy all the constraints provided by asteroseismology. We revisit the role of a candidate process whose efficiency scales with the contrast between the rotation rate of the core and the surface which was proposed to be related to the azimuthal magneto-rotational instability (AMRI) by Spada et al. We compute stellar evolution models of low- and intermediate-mass stars with the parametric formulation of AM transport proposed by Spada et al. until the end of the core-helium burning for low- and intermediate-mass stars and compare our results to the latest asteroseismic constraints available in the post main sequence phase. Both hydrogen-shell burning stars in the red giant branch and core-helium burning stars of low- and intermediate-mass in the mass range $1 M_{\odot} \lesssim M \lesssim 2.5 M_{\odot}$ can be simultaneously reproduced by this kind of parametrisation. Given current constraints from asteroseismology, the core rotation rate of post-main sequence stars seems to be well explained by a process whose efficiency is regulated by the internal degree of differential rotation in radiative zones.