Reaching Higher Densities for Laboratory White Dwarf Photospheres to Measure Spectroscopic Line Profiles

TL;DR

This study extends laboratory measurements of white dwarf atmosphere line profiles to higher electron densities, revealing divergences among models and aiding in their validation and the study of occupation probabilities.

Contribution

It provides experimental data at higher densities than previously benchmarked, testing and constraining theoretical line-profile models for white dwarf atmospheres.

Findings

Divergence observed between line-shape models at high densities

Experimental validation of line profiles beyond previous benchmarks

Measurement of occupation probabilities from line strengths

Abstract

As part of our laboratory investigation of the theoretical line profiles used in white dwarf atmosphere models, we extend the electron-density ($n_{\rm e}$) range measured by our experiments to higher densities (up to $n_{e}\sim80\times10^{16}$ cm$^{-3}$). Whereas inferred parameters using the hydrogen-$\beta$ spectral line agree among different line-shape models for $n_{\rm e}\lesssim30\times10^{16}$ cm$^{-3}$, we now see divergence between models. These are densities beyond the range previously benchmarked in the laboratory, meaning theoretical profiles in this regime have not been fully validated. Experimentally exploring these higher densities enables us to test and constrain different line-profile models, as the differences in their relative H-Balmer line shapes are more pronounced at such conditions. These experiments also aid in our study of occupation probabilities because we can measure these from relative line strengths.