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Title: Laboratory measurements of white dwarf photospheric spectral lines: Hβ

We spectroscopically measure multiple hydrogen Balmer line profiles from laboratory plasmas to investigate the theoretical line profiles used in white dwarf (WD) atmosphere models. X-ray radiation produced at the Z Pulsed Power Facility at Sandia National Laboratories initiates plasma formation in a hydrogen-filled gas cell, replicating WD photospheric conditions. We also present time-resolved measurements of Hβ and fit this line using different theoretical line profiles to diagnose electron density, n e, and n = 2 level population, n 2. Aided by synthetic tests, we characterize the validity of our diagnostic method for this experimental platform. During a single experiment, we infer a continuous range of electron densities increasing from n e ~ 4 to ~30 × 10 16 cm -3 throughout a 120-ns evolution of our plasma. Also, we observe n 2 to be initially elevated with respect to local thermodynamic equilibrium (LTE); it then equilibrates within ~55 ns to become consistent with LTE. This also supports our electron-temperature determination of T e ~ 1.3 eV (~15,000 K) after this time. At n e≲ 10 17 cm -3, we find that computer-simulation-based line-profile calculations provide better fits (lower reduced χ 2) than the line profiles currently used in the WDmore » astronomy community. The inferred conditions, however, are in good quantitative agreement. Lastly, this work establishes an experimental foundation for the future investigation of relative shapes and strengths between different hydrogen Balmer lines.« less
Authors:
 [1] ;  [2] ;  [2] ;  [1] ;  [3] ;  [3] ;  [2]
  1. Univ. of Texas, Austin, TX (United States); Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
  2. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
  3. Univ. of Texas, Austin, TX (United States)
Publication Date:
Report Number(s):
SAND-2015-2799J
Journal ID: ISSN 1538-4357; 579911
Grant/Contract Number:
AC04-94AL85000
Type:
Accepted Manuscript
Journal Name:
The Astrophysical Journal
Additional Journal Information:
Journal Volume: 806; Journal Issue: 2; Journal ID: ISSN 1538-4357
Publisher:
Institute of Physics (IOP)
Research Org:
Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Sponsoring Org:
USDOE National Nuclear Security Administration (NNSA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS
OSTI Identifier:
1235283