Parameter-free Stark Broadening of Hydrogen Lines in DA White Dwarfs

TL;DR

This paper introduces a parameter-free model for Stark broadening of hydrogen lines in white dwarf atmospheres, leading to more accurate spectral analysis without ad-hoc parameters.

Contribution

It develops a new, parameter-free Stark broadening model incorporating non-ideal gas effects directly into line profile calculations for white dwarf atmospheres.

Findings

First grid of parameter-free model spectra for hot DA white dwarfs

Significant differences in atmospheric parameters compared to previous models

Improved accuracy in spectroscopic analysis of white dwarf stars

Abstract

We present new calculations for the Stark broadening of the hydrogen line profiles in the dense atmospheres of white dwarf stars. Our improved model is based on the unified theory of Stark broadening from Vidal, Cooper & Smith, but it also includes non-ideal gas effects from the Hummer & Mihalas occupation probability formalism directly inside the line profile calculations. This approach improves upon previous calculations that relied on the use of an ad-hoc free parameter to describe the dissolution of the line wing opacity in the presence of high electric microfields in the plasma. We present here the first grid of model spectra for hot Teff >~ 12,000 K DA white dwarfs that has no free parameters. The atmospheric parameters obtained from optical and UV spectroscopic observations using these improved models are shown to differ substantially from those published in previous studies.