Dielectronic recombination of Fe XXIII forming Fe XXII : Laboratory measurements and theoretical calculations

Savin, D.W. and Gwinner, G. and Grieser, M. and Repnow, R. and Schnell, M. and Schwalm, D. and Wolf, A. and Zhou, S.G. and Kieslich, S. and Muller, A. and Schippers, S. and Colgan, J. and Loch, S.D. and Badnell, N.R. and Chen, M.H. and Gu, M.F. (2006) Dielectronic recombination of Fe XXIII forming Fe XXII : Laboratory measurements and theoretical calculations. Astrophysical Journal, 642 (2). pp. 1275-1285. ISSN 0004-637X

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Abstract

We have measured resonance strengths and energies for dielectronic recombination (DR) of beryllium-like Fe XXIII forming boron-like Fe XXII via N = 2 -> N' = 2 and N = 2 -> N' = 3 core excitations. All measurements were carried out using the heavy-ion Test Storage Ring at the Max Planck Institute for Nuclear Physics (MPI-K) in Heidelberg, Germany. We have also calculated these resonance strengths and energies using three independent, perturbative, state-of-the-art theoretical techniques: the multiconfiguration Breit-Pauli (MCBP) method, the multiconfiguration Dirac-Fock (MCDF) method, and the Flexible Atomic Code (FAC). Overall reasonable agreement is found between our experimental results and these theoretical calculations. We have used our measurements to produce a Maxwellian-averaged DR rate coefficient for Fe XXIII. Our experimentally derived rate coefficient is estimated to be accurate to better that approximate to 20%. At temperatures where Fe XXIII is predicted to form in both photo-ionized and electron-ionized gas, we find mixed agreement between our experimental rate coefficient and previously published rate coefficients. We find good agreement at these temperatures between the experimentally derived rate coefficient and our MCBP, MCDF, and FAC results.