Recombination Rate Coefficients for KLL Di-electronic Satellite Lines of Fe XXV and Ni XXVII

Abstract

The unified method for total electron-ion recombination is extended to study the dielectronic satellite (DES) lines. These lines, formed from radiative decay of autoionizing states, are highly sensitive temperature diagnostics of astrophysical and laboratory plasma sources. The computation of the unified recombination rates is based on the relativistic Breit-Pauli R-matrix method and close coupling approximation. Extending the theoretical formulation developed earlier we present recombination rate coefficients for the 22 satellite lines of KLL complexes of helium-like Fe XXV and Ni XXVII. The isolated resonance approximation, commonly used throughout plasma modeling, treats these resonances essentially as bound features except for dielectronic capture into, and autoionization out of, these levels. A line profile or cross section shape is often assumed. On the other hand, by including the coupling between the autoionizing and continuum channels, the unified method gives the intrinsic spectrum of DES lines which includes not only the energies and strengths, but also the natural line or cross section shapes. A formulation is presented to derive autoionization rates from unified resonance strengths and enable correspondence with the isolated resonance approximation. While the rates compare very well with existing rates for the strong lines to <20%, the differences for weaker DES lines are larger. We also illustrate the application of the present results to the analysis of K ALPHA complexes observed in high-temperature X-ray emission spectra of Fe XXV and Ni XXVII. There are considerable differences with previous results in the total KLL intensity for Fe XXV at temperatures below the temperature of maximum abundance in coronal equilibrium. (Abbreviated Abstract)

21 pages, 5 figures, to appear in Physica Scripta

References in corpus (5)

• Self-Consistent R-matrix Approach To Photoionization And Unified Electron-Ion Recombination
• The 6.7 keV KALPHA complex of He-like iron in transient plasmas
• A study of the breakdown of the quasi-static approximation at high densities and its effect on the helium-like K ALPHA complex of nickel, iron, and calcium
• Electron-Ion Recombination Rate Coefficients and Photoionization Cross Sections for Astrophysically Abundant Elements. IX. Ni XXVI and Ni XXVII for UV and X-ray modeling
• High-temperature behaviour of the helium-like K ALPHA G ratio: the effect of improved recombination rate coefficients for calcium, iron, and nickel

Cited by in corpus (2)

• Multiwavelength campaign on Mrk 509 VII. Relative abundances of the warm absorber
• Atomic data activities by the OP and IP consortia: past, present and new perspectives within the VAMDC