The effect of rotation on fingering convection in stellar interiors

TL;DR

This study investigates how rotation influences fingering convection in stellar interiors, revealing minimal effects generally but identifying a case where large-scale vortices significantly enhance compositional transport, with implications for stellar mixing.

Contribution

The paper provides the first direct numerical simulation analysis of rotation effects on fingering convection at low Prandtl number, highlighting conditions that lead to large-scale vortex formation and increased mixing.

Findings

Rotation generally has little effect on vertical transport.

Large-scale vortices can form at low density ratios and low Rossby numbers.

Vortices significantly enhance compositional transport rates.

Abstract

We study the effects of rotation on the growth and saturation of the double-diffusive fingering (thermohaline) instability at low Prandtl number. Using direct numerical simulations, we estimate the compositional transport rates as a function of the relevant non-dimensional parameters - the Rossby number, inversely proportional to the rotation rate, and the density ratio which measures the relative thermal and compositional stratifications. Within our explored range of parameters, we generally find rotation to have little effect on vertical transport. However, we also present one exceptional case where a cyclonic large scale vortex (LSV) is observed at low density ratio and fairly low Rossby number. The LSV leads to significant enhancement in the fingering transport rates by concentrating compositionally dense downflows at its core. We argue that the formation of such LSVs could be relevant to solving the missing mixing problem in RGB stars.