Parameterization of the level-resolved radiative recombination rate coefficients for the SPEX code

TL;DR

This paper provides parameterized level-resolved radiative recombination rate coefficients for ions from hydrogen to zinc, enhancing spectral analysis accuracy in astrophysics.

Contribution

It introduces new parameterizations of RR rate coefficients for a wide range of ions, with high accuracy, for integration into the SPEX spectral analysis software.

Findings

Parameterizations achieve better than 5% accuracy for 99% of levels.

Data covers ions from H-like to Na-like, Z=1 to 30.

Most levels, especially high-shell, are less critical for astrophysical plasma interpretation.

Abstract

The level-resolved radiative recombination (RR) rate coefficients for H-like to Na-like ions from H (Z = 1) up to and including Zn (Z = 30) are studied here. For H-like ions, the quantum-mechanical exact photoionization cross sections for nonrelativistic hydrogenic systems are used to calculate the RR rate coefficients under the principle of detailed balance, while for He-like to Na-like ions, the archival data on ADAS are adopted. Parameterizations are made for the direct capture rates in a wide temperature range. The fitting accuracies are better than 5% for about 99% of the 30, 000 levels considered here. The 1% exceptions include levels from low- charged many-electron ions, and/or high-shell (n>=4) levels are less important in terms of interpreting X-ray emitting astrophysical plasmas. The RR data will be incorporated into the high-resolution spectral analysis package SPEX.