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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]

Being the backbone element of deoxyribonucleic acid, phosphorus is a key component in the search for life in the Universe. To aid in its detection, we present line emissivity ratios for the five lowest-lying forbidden [P  ii ] transitions, namely those among the levels 3s23p2(3P0, 3P1, 3P2, 1D2, and 1S0). The wavelengths range between 0.44 and 70 µm, and several lie within the spectroscopic domain observable with the JWST. These line ratios have been calculated using a new collisional-radiative-cascade (CRR) model combining calculated collision strengths and level-specific recombination rate coefficients, with both data sets computed using the accurate Breit–Pauli R-matrix method. The CRR model includes a new scheme for (e + ion) recombination to emission-line formation. We compare its effect to models incorporating only electron-impact excitation and spontaneous radiative decay. We find that (e + ion) recombination has a significant impact on all line ratios, and represents a major improvement in physical accuracy of emission-line models. [ABSTRACT FROM AUTHOR]

Phosphorus abundance is crucial for DNA-based extraterrestrial life in exoplanets. Atomic data for observed spectral lines of P-ions are needed for its accurate determination. We present the first calculations for collision strengths for the forbidden [P  iii ] fine structure transition $$\mathrm{ 3s^23p (^2P^o_{1/2{\text{--}}3/2})}$$ within the ground state at 17.9 $$\mu$$ m , as well as allowed UV transitions in the $$\mathrm{ 3s^23p (^2P^o_{1/2,3/2}) \rightarrow 3s3p^2 (^2D_{3/2,5/2}, ^2S_{1/2}, ^2P_{1/2,3/2})}$$ multiplets between 915 and 1345 Å. Collision strengths are computed using the Breit–Pauli R-Matrix method including the first 18 levels, and they exhibit extensive auto-ionizing resonance structures. In particular, the Maxwellian averaged effective collision strength for the FIR 17.9 $$\mu$$ m  transition shows a factor 3 temperature variation broadly peaking at typical nebular temperatures. Its theoretical emissivity with solar phosphorus abundance is computed relative to H β and found to be similar to observed intensities from planetary nebulae; the abundances derived in earlier works are 3–5 times sub-solar. The results pertain to the reported paucity of phosphorus from preferred production sites in supernovae, and abundances in planetary nebulae and supernova remnants. [ABSTRACT FROM AUTHOR]

ABSTRACT Far-infrared and optical [O iii] lines are useful temperature-density diagnostics of nebular as well as dust obscured astrophysical sources. Fine-structure transitions among the ground state levels 1 s22 s22 p33 P 0,1,2 give rise to the 52- and 88-m lines, whereas transitions among the 3 P 0,1,2, 1 D 2, 1 S 0 levels yield the well-known optical lines λλ4363, 4959 and 5007 Å. These lines are excited primarily by electron impact excitation. However, despite their importance in nebular diagnostics collision strengths for the associated fine-structure transitions have not been computed taking full account of relativistic effects. We present Breit-Pauli R-matrix calculations for the collision strengths with highly resolved resonance structures. We find significant differences of up to 20 per cent in the Maxwellian averaged rate coefficients from previous works. We also tabulate these to lower temperatures down to 100 K to enable determination of physical conditions in cold dusty environments such photodissociation regions and ultraluminous infrared galaxies observed with the Herschel Space Observatory. We also examine the effect of improved collision strengths on temperature- and density-sensitive line ratios. [ABSTRACT FROM AUTHOR]

Time-dependent numerical simulations of the Kα complex of Fe xxvare carried out as a function of temperature–density–radiation field variations in high-temperature astrophysical and laboratory plasmas. In addition to several well-known features, the transient and steady-state spectra reveal the effects due to (a) time-dependent thermal and non-thermal radiation fields, (b) photo- and collisional excitation and ionization, and (c) high densities, on the‘quartet’ of principallines, and dielectronic satellites. The highly detailed models show precisely how, assuming a temporal–temperature correlation, the X-ray intensity varies between 6.6 and 6.7 keV and undergoes a‘spectral inversion’ in thewandzline intensities, characterizing an ionization- or a recombination-dominated plasma. The dielectronic satellite intensities are the most temperature-dependent features, but insensitive to density variations, and significantly contribute to the Kα complex forleading to asymmetric profiles. The 6.7-keV Kα complex should be a potential diagnostic of X-ray flares in active galactic nuclei, afterglows in gamma-ray bursts, and other non-equilibrium sources with the high-resolution measurements possible from the upcoming missionAstro-E2. It is also shown that high electron densities attenuate the line intensities in simulations relevant to laboratory plasmas, such as in inertial confinement fusion, laser, or magnetic Z-pinch devices. [ABSTRACT FROM AUTHOR]

ABSTRACT The Kα resonance complexes in oxygen ions O i–O viare theoretically computed, and resonance oscillator strengths and wavelengths are presented. The highly resolved photoionization cross-sections, with relativistic fine structure, are computed in the coupled channel approximation using the Breit–Pauli R-matrix method. A number of strong Kα resonances are found to be appreciable, with resonance oscillator strengths f[sub r] > 0.1 . The Kα resonance wavelengths of O i–O vilie in the relatively narrow wavelength range 22–23.5 Å, and the X-ray opacity in this region should therefore be significantly affected by K → L transitions in oxygen. The results should be useful in the interpretation of soft X-ray spectra observed from Chandra and XMM–Newton. [ABSTRACT FROM AUTHOR]

Asserts the domination of dielectronic satellites (DES) to the X-ray spectral formation in the 607-keV Kα complex of Fexxv. Definitions of diagnostic line ratio, DES and the lines with parameters from new relativistic atomic calculations; Source of the DES absorption resonance strengths from differential oscillator strengths; Assertion of the DES contribution to highly ionized iron.

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]