# Detailed opacity calculations for astrophysical applications

## TL;DR

This paper presents precise spectral opacity calculations for astrophysical applications, emphasizing the importance of laboratory experiments to validate data, with a focus on iron opacity relevant to stellar oscillations and solar interior models.

## Contribution

It introduces state-of-the-art opacity calculations and compares them with experimental data, highlighting discrepancies and theoretical considerations for astrophysical modeling.

## Key findings

- Measured iron opacity at Sandia Z-machine exceeds predictions.
- Laboratory spectra are systematically compared with SCO-RCG code.
- Discussion of density effects and autoionization in opacity calculations.

## Abstract

Nowadays, several opacity codes are able to provide data for stellar structure models, but the computed opacities may show significant differences. In this work, we present state-of-the-art precise spectral opacity calculations, illustrated by stellar applications. The essential role of laboratory experiments to check the quality of the computed data is underlined. We review some X-ray and XUV laser and Z-pinch photo-absorption measurements as well as X-ray emission spectroscopy experiments involving hot dense plasmas produced by ultra-high-intensity laser irradiation. The measured spectra are systematically compared with the fine-structure opacity code SCO-RCG. Focus is put on iron, due to its crucial role in understanding asteroseismic observations of $\beta$ Cephei-type and Slowly Pulsating B stars, as well as of the Sun. For instance, in $\beta$ Cephei-type stars, the iron-group opacity peak excites acoustic modes through the "kappa-mechanism". A particular attention is paid to the higher-than-predicted iron opacity measured at the Sandia Z-machine at solar interior conditions. We discuss some theoretical aspects such as density effects, photo-ionization, autoionization or the "filling-the-gap" effect of highly excited states.