Influence of the number of atomic levels on the spectral opacity of low temperature nickel and iron in the spectral range 50–300 eV

Abstract

Abstract. Opacity is a fundamental ingredient for the secular evolution of stars. The calculation of the stellar plasma absorption coefficients is complex due to the composition of these plasmas, generally an H /He dominated mixture with a low concentration of partially ionized heavy ions (the iron group). The international collaboration OPAC recently presented extensive comparisons of spectral opacities of iron and nickel for temperatures between 15 and 40 eV and for densities of ∼ 3 mg/cm 3 , relevant to the stellar envelope conditions [1,2]. The role of Configuration Interaction (CI) and the influence of the number of atomic levels on the opacity using the recently improved version of HULLAC atomic code [3,4] are illustrated in this article. Comparisons with theoretical predictions already presented in [1] are discussed.

Iron and Nickel spectral opacity calculations in conditions relevant for pulsating stellar envelopes and experiments

“…In a companion paper, definitions and illustrations of these calculations are given [7]. In this paper we also present HULLAC-v9 predictions for two sets of experimental conditions typical of 1/ Da Silva et al experiment on iron [8] and 2/ LULI 2010 experiment first analysis on nickel [2].…”

“…In this study, the role of CI and the influence of the number of excited levels is discussed, thanks to the new version of HULLAC-v9 code with full CI calculations. In a companion paper, definitions and illustrations of these calculations are given [7]. In this paper we compare also HULLAC-v9 predictions to two experimental conditions 1/ Da Silva et al (iron) [8,9] and 2/ LULI 2010 experiment (nickel) first analysis [2].…”

“…In HULLAC-v9 and OP calculations full Configuration Interaction (CI) can be included [5,6,10]. In HULLAC-v9, the computation of fine structure levels with CI (mode L for Levels) is chosen by the user for defined groups of levels (GRL), see [7]. Selecting the "CIinNRC" mode, HULLAC-v9 computes the usual Relativistic CI (RCI) between all levels of one Non Relativistic Configuration (NRC), see [5,6] for more details or illustrations.…”

“…We present and include in the opacity code comparisons new HULLAC-v9 calculations [5,6] that include full CI. To illustrate the importance of this effect we compare different CI approximations (modes) available in HULLAC-v9 [7]. These results are compared to previous predictions and to experimental data.…”