Mixing and Overshooting in Surface Convection Zones of DA White Dwarfs: First Results from ANTARES

TL;DR

This study presents the most extensive 3D hydrodynamical simulation of surface convection in a DA white dwarf, revealing detailed velocity decay patterns and implications for mixing and accretion processes.

Contribution

First high-resolution 3D simulation of a DA white dwarf's surface layers, providing new insights into convection and mixing beyond previous models.

Findings

Velocities decay more rapidly horizontally than vertically in wave-dominated regions.

Simulation results align with prior models in unstable and overshooting zones.

Implications for mixing extent influence white dwarf metal accretion estimates.

Abstract

We present results of a large, high resolution 3D hydrodynamical simulation of the surface layers of a DA white dwarf (WD) with $T_{\rm eff}=11800$ K and $\log(g)=8$ using the ANTARES code, the widest and deepest such simulation to date. Our simulations are in good agreement with previous calculations in the Schwarzschild-unstable region and in the overshooting region immediately beneath it. Farther below, in the wave-dominated region, we find that the rms horizontal velocities decay with depth more rapidly than the vertical ones. Since mixing requires both vertical and horizontal displacements, this could have consequences for the size of the region that is well mixed by convection, if this trend is found to hold for deeper layers. We discuss how the size of the mixed region affects the calculated settling times and inferred steady-state accretion rates for WDs with metals observed in their atmospheres.