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The Sun is the most studied of all stars, and thus constitutes a benchmark for stellar models. However, our vision of the Sun is still incomplete, as illustrated by the current debate on its chemical composition. The problem reaches far beyond chemical abundances and is intimately linked to microscopic and macroscopic physical ingredients of solar models such as radiative opacity, for which experimental results have been recently measured that still await the- oretical explanations. We present opacity profiles derived from helioseismic inferences and compare them with detailed theoretical computations of individual element contributions using three different opacity computation codes, in a complementary way to experimental results. We find that our seismic opacity is about 10% higher than theoretical values used in current solar models around 2 million degrees, but lower by 35% than some recent available theoretical values. Using the Sun as a laboratory of fundamental physics, we show that quantitative comparisons between various opacity tables are required to understand the origin of the discrepancies between reported helioseismic, theoretical and experimental opacity values. 

This work is part of the groundwork for iron opacity calculations for solar modeling. A B S T R A C T An extensive set of E1 transitions with spectral features for Fe V obtained using relativistic Breit–Pauli R-matrix (BPRM) method is presented. The results correspond to a larger amount of atomic data and of higher accuracy in comparison to the earlier R-matrix results. We report 1,712,655 transitions among 4300 fine structure levels with 𝑗 ≤ 10, 2𝑆 + 1 = 5, 3, 1, 𝐿 ≤ 10, of even and odd parities of n ≤ 10 and 𝑙 ≤ 9. The close coupling wavefunction expansion of Fe V includes ground and 18 excited levels of the core ion Fe VI. The theoretical spectroscopy of the fine structure levels for unique identifications was carried out using an algorithm based on quantum defect theory and angular algebra. The completeness of the calculated data sets is verified for all possible bound levels belonging to the relevant 𝐿𝑆 terms. The energies are in very good agreement with measured values within a few percent for most levels. Comparison of transition parameters and lifetimes also indicate general agreement with others. The present data processed for spectral features that show the detectability of Fe V is well within range of James Webb Space Telescope and other observatories. The present results for Fe VI, obtained from relativistic atomic structure calculations in Breit–Pauli approximation using code SUPERSTRUCTURE, include allowed E1 and forbidden E2, M1, E3, M2 transitions, 506,512 in total among 1021 energy levels, bound and continuum. Calculations show much larger number of bound levels of configurations of 3𝑠23𝑝53𝑑4 than those listed at NIST compilation table. The calculations included an optimized set of 9 configurations with orbitals going up to 4f. Comparison of energies, oscillator strengths, lifetimes with available values show good agreement although some large differences are also noted. In contrast to Fe V, the spectral features of Fe VI show three regions of strong lines in the soft-xray to ultraviolet wavelengths.