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Experimentally Derived Dielectronic Recombination Rate Coefficients For Helium-Like C V and Hydrogenic O VIII

Savin, Daniel Wolf

Using published measurements of dielectronic recombination (DR) resonance strengths and energies for C V to C IV and O VIII to O VII, we have calculated the DR rate coefficient for these ions. Our derived rates are in good agreement with multiconfiguration, intermediate-coupling and multiconfiguration, fully relativistic calculations, as well as with most LS-coupling calculations. Our results are not in agreement with the recommended DR rates commonly used for modeling cosmic plasmas. We have used theoretical radiative recombination (RR) rates in conjunction with our derived DR rates to produce a total recombination rate for comparison with unified RR + DR calculations in LS coupling. Our results are not in agreement with undamped, unified calculations for C V but are in reasonable agreement with damped, unified calculations for O VIII. For C V, the Burgess general formula (GF) yields a rate that is in very poor agreement with our derived rate. The Burgess and Tworkowski modification of the GF yields a rate that is also in poor agreement. The Merts et al. modification of the GF yields a rate that is in fair agreement. For O VIII, the GF yields a rate that is in fair agreement with our derived rate. The Burgess and Tworkowski modification of the GF yields a rate that is in good agreement, and the Merts et al. modification yields a rate that is in very poor agreement. These results suggest that for ΔN = 1 DR, it is not possible to know a priori which formula will yield a rate closer to the true DR rate. We describe the technique used to obtain DR rate coefficients from laboratory measurements of DR resonance strengths and energies. For use in plasma modeling, we also present easy-to-use fitting formulae for the experimentally derived DR rates.

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Title
The Astrophysical Journal
DOI
https://doi.org/10.1086/307772

More About This Work

Academic Units
Astronomy and Astrophysics
Published Here
March 15, 2013
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