Detailed opacity calculations for astrophysical applications

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 β Cephei-type and Slowly Pulsating B stars, as well as of the Sun. For instance, in β Cephei-type stars, the iron-group opacity peak excites acoustic modes through the "kappa-mechanism". A particular attention is paid to the higher-thanpredicted 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.

Plasma opacity calculations using the Starrett and Saumon average-atom model with ion correlations

“…If the method to evaluate the chemical potential in the up-to-date version of the Starrett and Saumon model does not lead to significant inaccuracies, the account of ion correlations appears to be not very important in the context of the solar opacity problem, thus favoring the assumption that this problem is caused by the existence of some unaccounted deficiencies of the solar modeling (see, e.g., Ref. [15]) rather than by any substantial inaccuracies in the theoretical opacity data.…”

“…It is important to note that detailed calculations of solar opacities using those models, e.g. ATOMIC [7][8][9], OPAS [10][11][12], and SCO-RCG [13][14][15] as well as the earlier OP (Opacity Project) [16][17][18][19] and OPAL [20] calculations, yield similar results, being however unable to explain the data of helioseismic observations and neutrino measurements. This contradiction along with the unexpected results of the Z-machine experiment [6] have spurred the efforts to reveal further potential improvements of theoretical opacity data [15,21,22].…”