Pure-hydrogen 3D model atmospheres of cool white dwarfs

TL;DR

This paper presents 3D pure-hydrogen atmosphere models for cool white dwarfs, showing significant convective property variations and demonstrating their superiority over 1D models in spectroscopic analysis and mass distribution accuracy.

Contribution

It introduces detailed 3D models for DA white dwarfs, highlighting their insensitivity to numerical parameters and improved spectral analysis over traditional 1D models.

Findings

3D models show significant convective property variations.

3D spectra improve white dwarf mass distribution estimates.

1D models fail to account for convective overshoot effects.

Abstract

A sequence of pure-hydrogen CO5BOLD 3D model atmospheres of DA white dwarfs is presented for a surface gravity of log g = 8 and effective temperatures from 6000 to 13,000 K. We show that convective properties, such as flow velocities, characteristic granulation size and intensity contrast of the granulation patterns, change significantly over this range. We demonstrate that these 3D simulations are not sensitive to numerical parameters unlike the 1D structures that considerably depend on the mixing-length parameters. We conclude that 3D spectra can be used directly in the spectroscopic analyses of DA white dwarfs. We confirm the result of an earlier preliminary study that 3D model spectra provide a much better characterization of the mass distribution of white dwarfs and that shortcomings of the 1D mixing-length theory are responsible for the spurious high-log g determinations of cool white dwarfs. In particular, the 1D theory is unable to account for the cooling effect of the convective overshoot in the upper atmospheres.