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Peer-reviewedCC BY 4.0The Astrophysical Journal

A New Approach to Modeling Line Shapes with Quasi-H 2 + Satellites in Stellar Atmospheres

  • Jackson R. White1,2
  • Thomas A. Gomez3,4
  • Mark C. Zammit2
  • Michael H. Montgomery1
  • Bart H. Dunlap1
  • Ivan Hubeny5
  • Dmitry V. Fursa6
  • Igor Bray6
  • Don E. Winget1
6 affiliations
  1. 1University of Texas at Austin
  2. 2Los Alamos National Laboratory
  3. 3University of Colorado
  4. 4University of Michigan
  5. 5University of Arizona
  6. 6Curtin University
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Abstract

Theoretical spectral line shapes describe the distribution of opacity due to bound electronic transitions in hot dense plasmas, and are used to fit emergent spectra from many astrophysical sources. Deficiencies in line broadening theory have been proposed as a possible explanation for unresolved discrepancies between theoretical and observed spectra in white dwarf star atmospheres and laboratory experiments at white dwarf star photosphere conditions. One possible source of these discrepancies is the formation of quasi-molecules. Quasi-molecules are close (unbound) collisions between atoms, which broaden line shapes and create additional satellite lines. Quasi-molecules are challenging to implement into traditional line shape codes and have historically required a number of physical approximations beyond what is used in standard Stark broadening models. Here we present a new approach to calculating line shapes with quasi-molecular H 2 + resonances, using a novel multiple-basis method that considers both atomic and molecular states. We implement this approach into a simulation line shape code, present hydrogen Lyman-series line shapes with quasi-H 2 + resonances, and demonstrate the impact our new line shapes have on hydrogen-atmosphere white dwarf star model spectra. We find that our new approach leads to broader quasi-molecular features that agree well with observed spectra in initial comparisons.

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Cite

BibTeXRIS
BibTeX
@article{white2026approach,
  title = {{A New Approach to Modeling Line Shapes with Quasi-H 2 + Satellites in Stellar Atmospheres}},
  author = {Jackson R. White and Thomas A. Gomez and Mark C. Zammit and Michael H. Montgomery and Bart H. Dunlap and Ivan Hubeny and Dmitry V. Fursa and Igor Bray and Don E. Winget},
  journal = {The Astrophysical Journal},
  year = {2026},
  month = sep,
  doi = {10.3847/1538-4357/ae8f2d},
  url = {https://iopscience.iop.org/article/10.3847/1538-4357/ae8f2d},
  note = {CC BY 4.0},
}
RIS
TY  - JOUR
TI  - A New Approach to Modeling Line Shapes with Quasi-H 2 + Satellites in Stellar Atmospheres
AU  - Jackson R. White
AU  - Thomas A. Gomez
AU  - Mark C. Zammit
AU  - Michael H. Montgomery
AU  - Bart H. Dunlap
AU  - Ivan Hubeny
AU  - Dmitry V. Fursa
AU  - Igor Bray
AU  - Don E. Winget
PY  - 2026
DA  - 2026/09/30
JO  - The Astrophysical Journal
DO  - 10.3847/1538-4357/ae8f2d
UR  - https://iopscience.iop.org/article/10.3847/1538-4357/ae8f2d
AB  - Theoretical spectral line shapes describe the distribution of opacity due to bound electronic transitions in hot dense plasmas, and are used to fit emergent spectra from many astrophysical sources. Deficiencies in line broadening theory have been proposed as a possible explanation for unresolved discrepancies between theoretical and observed spectra in white dwarf star atmospheres and laboratory experiments at white dwarf star photosphere conditions. One possible source of these discrepancies is the formation of quasi-molecules. Quasi-molecules are close (unbound) collisions between atoms, which broaden line shapes and create additional satellite lines. Quasi-molecules are challenging to implement into traditional line shape codes and have historically required a number of physical approximations beyond what is used in standard Stark broadening models. Here we present a new approach to calculating line shapes with quasi-molecular H 2 + resonances, using a novel multiple-basis method that considers both atomic and molecular states. We implement this approach into a simulation line shape code, present hydrogen Lyman-series line shapes with quasi-H 2 + resonances, and demonstrate the impact our new line shapes have on hydrogen-atmosphere white dwarf star model spectra. We find that our new approach leads to broader quasi-molecular features that agree well with observed spectra in initial comparisons.
SN  - 0004-637X
SN  - 1538-4357
ER  -