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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]

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]