On the Chemical Mixing Induced by Internal Gravity Waves (IGW)

TL;DR

This paper uses 2D hydrodynamic simulations to quantify how internal gravity waves induce chemical mixing in stars, providing a diffusion model that can improve stellar evolution predictions.

Contribution

It introduces a new parametrization for chemical mixing driven by internal gravity waves based on wave amplitude, suitable for incorporation into stellar models.

Findings

Mixing by IGW can be modeled as a diffusion process.

Diffusion coefficient depends on wave amplitude, not local fluid velocity.

Provides a simple parametrization for stellar evolution codes.

Abstract

Detailed modeling of stellar evolution requires a better understanding of the (magneto-)hydrodynamic processes which mix chemical elements and transport angular momentum. Understanding these pro- cesses is crucial if we are to accurately interpret observations of chemical abundance anomalies, surface rotation measurements and asteroseismic data. Here, we use two-dimensional hydrodynamic simula- tions of the generation and propagation of internal gravity waves (IGW) in an intermediate mass star to measure the chemical mixing induced by these waves. We show that such mixing can generally be treated as a diffusive process. We then show that the local diffusion coefficient does not depend on the local fluid velocity, but rather on the wave amplitude. We then use these findings to provide a simple parametrization for this diffusion which can be incorporated into stellar evolution codes and tested against observations.