Abstract

White Dwarf (WD) stars are the most common stellar remnant in the universe. WDs usually have a hydrogen or helium atmosphere, and helium WD (called DB) spectra can be used to solve outstanding problems in stellar and galactic evolution. DB origins, which are still a mystery, must be known to solve these problems. DB masses are crucial for discriminating between different proposed DB evolutionary hypotheses. Current DB mass determination methods deliver conflicting results. The spectroscopic mass determination method relies on line broadening models that have not been validated at DB atmosphere conditions. We performed helium benchmark experiments using the White Dwarf Photosphere Experiment (WDPE) platform at Sandia National Laboratories' Z-machine that aims to study He line broadening at DB conditions. Using hydrogen/helium mixture plasmas allows investigating the importance of He Stark and van der Waals broadening simultaneously. Accurate experimental data reduction methods are essential to test these line-broadening theories. In this paper, we present data calibration methods for these benchmark He line shape experiments. We give a detailed account of data processing, spectral power calibrations, and instrument broadening measurements. Uncertainties for each data calibration step are also derived. We demonstrate that our experiments meet all benchmark experiment accuracy requirements: WDPE wavelength uncertainties are <1 Å, spectral powers can be determined to within 15%, densities are accurate at the 20% level, and instrumental broadening can be measured with 20% accuracy. Fulfilling these stringent requirements enables WDPE experimental data to provide physically meaningful conclusions about line broadening at DB conditions.

Highlights

  • White Dwarf (WD) stars are the end point of stellar evolution for nearly 98% of all stars including our sun.[1]

  • We demonstrate that our experiments meet all benchmark experiment accuracy requirements: White Dwarf Photosphere Experiment (WDPE) wavelength uncertainties are

  • The spectral power calibration is critical to the WDPE since it allows for the self-emission correction of absorption spectra

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Summary

INTRODUCTION

White Dwarf (WD) stars are the end point of stellar evolution for nearly 98% of all stars including our sun.[1]. The above-described platform developed for benchmark hydrogen line shape experiments can be extended to test van der Waals and Stark broadening models and thereby shed light on DB origins and associated astrophysical problems. For these benchmark experiments, a hydrogen–helium gas mixture is used. Data calibration is the remaining challenge for performing He benchmark experiments This requires accurate wavelength and spectral power calibrations and reliable electron and neutral density measurements. At the end of our data calibration process, we are left with benchmark experimental data that allows us to validate van der Waals and Stark broadening models at DB atmosphere conditions.

THE WDPE AT SANDIA NATIONAL LABORATORIES’ Z-MACHINE
PREPARING WDPE SPECTRA FOR COMPARISONS WITH ATOMIC MODELS
Basic CCD data corrections
CCD spectral power calibrations
DATA CALIBRATION UNCERTAINTIES
Wavelength uncertainty
Spectral power calibration uncertainty
Instrumental broadening uncertainty
Findings
CONCLUDING REMARKS
Full Text
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