Solution to the problem of the surface gravity distribution of cool DA white dwarfs from improved 3D model atmospheres

TL;DR

This study uses advanced 3D hydrodynamical models to correct the surface gravity measurements of cool DA white dwarfs, resolving previous discrepancies caused by simplified convection treatments.

Contribution

It introduces 3D model atmospheres for cool white dwarfs, providing more accurate surface gravity estimates compared to traditional 1D models.

Findings

3D models predict lower, more accurate surface gravities.

Corrected gravities align with expectations for these stars.

The approach reduces the high-log g problem in cool white dwarfs.

Abstract

The surface gravities of cool (Teff < 13,000 K) hydrogen-atmosphere DA white dwarfs, determined from spectroscopic analyses, are found to be significantly higher than the canonical value of log g ~ 8 expected for these stars. It was recently concluded that a problem with the treatment of convective energy transport within the framework of the mixing-length theory was the most plausible explanation for this high-log g problem. We pursue the investigation of this discrepancy by computing model spectra of cool convective white dwarfs from a small sequence (11,300 K < Teff < 12,800 K) of 3D hydrodynamical model atmospheres, which feature a sophisticated treatment of convection and radiative transfer. Our approach is to proceed with a differential analysis between 3D and standard 1D models. We find that the 3D spectra predict significantly lower surface gravities, with corrections of the right amplitude as a function of effective temperature to obtain values of log g ~ 8 on average. We conclude that the surface gravity distribution of cool convective DA white dwarfs is much closer to that of hotter radiative objects when using, for the treatment of the convection, 3D models instead of the mixing-length framework.