Re-analysis of plasma temperature and density for stellar iron opacity experiments

Iron opacities measured at stellar interior conditions were significantly higher than calculated [Bailey, Nature 517, 56 (2015)]. While this helps resolve a decade old solar problem, the question remains: What is responsible for the model-data discrepancy? One recurring question is the accuracy of plasma temperature and density. Accurate determination of plasma conditions are challenging due to multiple sources of uncertainties such as uncertainties due to spectral-line-broadening model, background subtraction, areal density, and analysis method itself. Specifically, uncertainty in the line-broadening models was raised as a serious concern [Nagayama HEDP 2016, Iglesias HEDP 2016]. Recently, the line-shape theory was refined by removing three common approximations. The background determination methods were also improved. Here, we reanalyze the temperature and density of the iron opacity data using the latest line-broadening model and the background determination methods. We also discuss the trade offs between an analysis strategy that infers all desired plasma parameters from the entire spectrum at once and an alternative strategy that infers one plasma parameter at a time using only the spectral features that provide the most sensitivity to the individual parameters. We will summarize the changes in the inferred conditions and its impact on the reported model-data opacity discrepancies.