Chemical Mixing Induced by Internal Gravity Waves in Intermediate Mass Stars

TL;DR

This study investigates how internal gravity waves induce mixing in intermediate-mass stars, revealing that mixing varies with age and mass, and provides a prescription for incorporating this into stellar evolution models.

Contribution

The paper extends previous work by analyzing IGW-induced mixing across different stellar masses and ages, offering a practical prescription for 1D stellar models.

Findings

Mixing profiles vary significantly with stellar age.

More massive stars exhibit stronger mixing.

A prescription for including IGW mixing in 1D models is provided.

Abstract

Internal gravity waves (IGWs) can cause mixing in the radiative interiors of stars. We study this mixing by introducing tracer particles into two - dimensional (2D) hydrodynamic simulations. Following the work of Rogers & McElwaine (2017), arXiv:1709.04920, we extend our study to different masses (3 M$_{\odot}$, 7 M$_{\odot}$ and 20 M$_{\odot}$) and ages (ZAMS, midMS and TAMS). The diffusion profiles of these models are influenced by various parameters such as the Brunt-V\"ais\"al\"a frequency, density, thermal damping, the geometric effect and the frequencies of waves contributing to these mixing profiles. We find that the mixing profile changes dramatically across age. In younger stars, we noted that the diffusion coefficient increases towards the surface, whereas in older stars the initial increase in the diffusion profile is followed by a decreasing trend. We also find that mixing is stronger in more massive stars. Hence, future stellar evolution models should include this variation. In order to aid the inclusion of this mixing in one-dimensional (1D) stellar evolution models, we determine the dominant waves contributing to these mixing profiles and present a prescription that can be included in 1D models.