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The dependence of the Rosseland Mean Opacity (RMO) on the equation of state and the number of included atomic levels of iron ions prevalent at the solar radiative/convection boundary is investigated. The 'chemical picture' Mihalas–Hummer–Däppen (MHD) equation-of-state (EOS), and its variant QMHD–EOS, are studied at two representative temperature–density sets at the base of the convection zone and the Sandia Z experiment: (2 × 106 K, 1023/cc) and (2.11 × 106 K, 3.16 × 1022/cc), respectively. It is found that whereas the new atomic data sets from accurate R-matrix calculations for opacities (RMOP) are vastly overcomplete, involving hundreds to over a thousand levels of each of the three Fe ions considered – Fe  xvii , Fe  xviii , Fe  xix – the EOS constrains contributions to RMOs by relatively fewer levels. The RMOP iron opacity spectrum is quite different from the Opacity Project distorted wave model and shows considerably more plasma broadening effects. This work points to possible improvements needed in the EOS for opacities in high-energy–density plasma sources. [ABSTRACT FROM AUTHOR]

Based on new calculations, we reconfirm the low- and high-density limits on the forbidden fine-structure line intensity ratio [O ii] and . Employing [O ii] collision strengths calculated using the Breit–Pauli -matrix method, we rule out any significant deviation due to relativistic effects from these canonical values. The present results are in substantial agreement with older calculations by Pradhan, and validate the extensive observational analyses of gaseous nebulae by Copetti & Writzel and Wang et al. that reach the same conclusions. The present theoretical results and the recent observational analyses differ significantly from the calculations by McLaughlin & Bell and Keenan et al. The new Maxwellian averaged effective collision strengths are presented for the 10 transitions among the first five levels to enable computations of [O ii] line ratios. [ABSTRACT FROM AUTHOR]