Dielectronic recombination for oxygenlike ions relevant to astrophysical applications

In the modeling of the astrophysical plasmas, the relative elemental abundance inferred from solar and stellar upper atmosphere can be affected by as much as a factor of 5 due to the uncertainties in the current dielectronic recombination (DR) rate coefficients used to analyze the spectra [Savin and Laming, Astrophys. J. 566, 1166 (2002)]. DR rate coefficients for oxygenlike ions have been identified as the most urgent needs for the astrophysical applications. In this work, we report on the calculations of DR rate coefficients for Mg V, Si VII, S IX, and Fe XIX ions which are important for the modeling of the astrophysical plasmas. The calculations are carried out in isolated resonance and distorted-wave approximations. The relevant atomic data are calculated using the multiconfigurational Dirac-Fock method. We include 2s-2p, 2p(1/2)-2p(3/2), 2l-3l('), and 1s-2p excitations and cover temperatures ranging from 0.001 eV to 10 000 eV. For low temperatures, it is essential to have accurate DR resonance energies and to include fine-structure excitations in order to obtain reliable DR rate coefficients. Good agreement with experiment has been found for Fe XIX. For Mg V, Si VII, and S IX, significant discrepancies are noted between this work and recommended rate coefficients.