# Magnetized fingering convection in stars

## TL;DR

This study tests and extends a model of magnetized fingering convection in stars, revealing its limitations and improving its accuracy for stellar conditions, which impacts understanding of stellar mixing processes.

## Contribution

The paper provides an extended model for magnetized fingering convection that better predicts chemical mixing rates across a wider parameter space in stellar environments.

## Key findings

- The original model does not always accurately predict mixing rates when magnetic diffusivity is high.
- An extended model improves prediction accuracy, especially near marginal stability conditions.
- Implications for stellar structure and evolution are discussed based on the new model.

## Abstract

Fingering convection (also known as thermohaline convection) is a process that drives the vertical transport of chemical elements in regions of stellar radiative zones where the mean molecular weight increases with radius. Recently, Harrington & Garaud (2019) used three-dimensional direct numerical simulations to show that a vertical magnetic field can dramatically enhance the rate of chemical mixing by fingering convection. Furthermore, they proposed a so-called "parasitic saturation" theory to model this process. Here, we test their model over a broad range of parameter space, using a suite of direct numerical simulations of magnetized fingering convection varying the magnetic Prandtl number, magnetic field strength, and composition gradient. We find that the rate of chemical mixing measured in the simulations is not always predicted accurately by their existing model, in particular when the magnetic diffusivity is large. We then present an extension of the Harrington & Garaud (2019) model which resolves this issue. When applied to stellar parameters, it recovers the results of Harrington & Garaud (2019) except in the limit where fingering convection becomes marginally stable, where the new model is preferred. We discuss the implications of our findings for stellar structure and evolution.