Co-existence of Internal Gravity Waves and Tayler-Spruit Magnetic Fields in the Radiative Core of Low-mass Stars

TL;DR

This study investigates how magnetic fields generated by the Tayler-Spruit dynamo influence internal gravity waves in low-mass stars, affecting their oscillation spectra and angular momentum transport.

Contribution

It models the interaction between TSD-generated magnetic fields and internal gravity waves, revealing their conversion into magneto-gravity waves during stellar evolution.

Findings

Low-frequency gravity waves can become magneto-gravity waves due to TSD magnetic fields.

Most internal gravity waves in red giants may convert into magneto-gravity waves in the core.

Magnetic fields influence angular momentum transport in stellar radiative zones.

Abstract

The Tayler-Spruit dynamo (TSD) is able to generate a small-scale magnetic field in the differentially rotating stably stratified layers of stars and was recently observed in numerical simulations. In parallel, the propagation of internal gravity waves in stars can be modified in the presence of a magnetic field. Here we first want to estimate the interaction between a magnetic field generated by the TSD and internal gravity waves in the radiative core of low-mass stars. This allows us to then characterise the effect of this interplay on the observed standing modes spectrum and on the internal transport of angular momentum by progressive waves. To do this, we use the STAREVOL evolution code to compute the structure of low-mass rotating stars along their evolution. In particular, we implement a formalism to describe the TSD and estimate the regions where the generated magnetic field is strong enough to change the identity of internal gravity waves to magneto-gravity waves. In addition, we evaluate the possible limitation of angular momentum transport by the combined action of rotation and magnetism. We show that along the pre-main sequence and main-sequence evolution, the lowest frequencies of the excited gravity wave spectrum could be converted to magneto-gravity waves by the magnetic field generated by the TSD. During the red-giant branch we find that most of the excited spectrum of progressive internal gravity waves could be converted into magneto-gravity waves in the very central region.