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Improved Simulations of Astrophysical Plasmas: Computation of New Dielectronic Recombination Data

Gorczyca, T. W.; Korista, K. T.; Zatsarinny, O.; Badnell, N. R.; Savin, Daniel Wolf

Here we recap the works of two posters presented at the 2002 NASA Laboratory Astrophysics Workshop. The first was Shortcomings of the R-Matrix Method for Treating Dielectronic Recombination. The second was Computation of Dielectronic Recombination Data for the Oxygen-Like Isoelectronic Sequence.(Shortcomings of the R-Matrix Method for Treating Dielectronic Recombination) By performing new radiation-damped R-matrix scattering calculations for the photorecombination of Fe17+ forming Fe16+, we demonstrate and discuss the difficulties and fundamental inaccuracies associated with the R-matrix method for treating dielectronic recombination (DR). Our new R-matrix results significantly improve upon earlier R-matrix Results for this ion. However, we show theoretically that all R-matrix methods are unable to account accurately for the phenomenon of radiative decay followed by autoionization. For Fe17+, we demonstrate numerically that this results in an overestimate of the DR cross section at the series limit, which tends to our analytically predicted amount of 40%. We further comment on the need for fine resonance resolution and the inclusion of radiation damping effects. Overall, slightly better agreement with experiment is still found with the results of perturbative calculations, which are computationally more efficient than R-matrix calculations by more than two orders of magnitude. TWG was supported in part by NASA Space Astrophysics Research and Analysis Program grant NAG5-10448. NRB was supported by UK PPARC grant PPA/G/S/1997/00783. DWS was supported in part by NASA Space Astrophysics Research and Analysis Program grant NAG5-5261.(Computation of Dielectronic Recombination Data for the Oxygen-Like Isoelectronic Sequence) We have systematically calculated rate coefficients for dielectronic recombination (DR) along the oxygen-like sequence. A recent benchmarking of DR resonance strength and energies between our theoretical techniques and the experimental results from the Test Storage Ring in Heidelberg has already shown fairly good agreement for the most highly-ionized oxygen-like system we consider here, DR of Fe XIX forming Fe XVIII. At the low-charge end of this isoelectronic sequence, we benchmark our results using F II DR data which are determined from measured neutral fluorine photoionization measurements and the principle of detailed balance. To assess the reliability of our calculations for intermediate Oxygen-like ionization stages, we compare between theoretical R-matrix and perturbative results. All calculations have been performed in intermediate-coupling, so that fine structure effects are incorporated. Furthermore, both Δ n=0 and Δ n>0 core transitions are included in order to span a higher temperature range. Final-state-resolved rate coefficients and total rate coefficients have been tabulated, and these data are available in either format from our web site.


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Academic Units
Astronomy and Astrophysics
Published Here
April 5, 2013


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