Laboratory Observations of Hydrogen Balmer Line Profiles

As the endpoints of stellar evolution, white dwarf stars contain a wealth of information about the star formation history of Galactic stellar populations, inform our understanding of cosmologically relevant type Ia supernovae, and provide us with proxy laboratories for studying matter at extreme energy densities. These and many other results stemming from the observations of white dwarf stars depend on accurate white dwarf model spectra, which, in turn, depend on accurate theoretical line profiles. The white dwarf photosphere experiment uses the Z machine at Sandia National Labs to recreate the plasma conditions observed in the line-forming regions of white dwarf atmospheres (1 – 2 eV and 10¹⁶ – 10¹⁸ cm^-3) with the goal of making benchmark measurements of line profiles. In this talk, we review our progress in measuring hydrogen Balmer line profiles in absorption and emission, including measurements at higher densities (~ 10¹⁸ cm^-3). We also discuss existing model uncertainties and how these and future measurements can provide useful constraints.