Converged Close-Coupling R-Matrix calculations of Photoionization of Fe XVII in Astrophysical Plasmas: from Convergence to Completeness

TL;DR

This study combines R-Matrix and Distorted Wave methods to improve photoionization cross section calculations for Fe XVII, addressing resonance structures and background contributions to astrophysical plasma opacity.

Contribution

It introduces a comprehensive approach that merges R-Matrix and Distorted Wave calculations to enhance the completeness and accuracy of photoionization data for Fe XVII.

Findings

Good agreement between RDW and BPRM for background cross sections.

Top-up contribution increases opacity estimates by approximately 20%.

Overall enhancement of Rosseland Mean Opacity by about 55% over previous models.

Abstract

Extensive resonance structures are manifest in R-Matrix (RM) calculations. However, there exist a large number of highly excited electronic configurations that may contribute to background non-resonant bound-free opacity in high-temperature plasmas. Since RM calculations are very complex, and not essential for background contributions, the Relativistic Distorted Wave (RDW) method is utilized to complement ("top-up") photoionization cross sections of Fe XVII obtained using Close-Coupling Breit-Pauli R-Matrix (CC-BPRM) method. There is good agreement between RDW and BPRM for background cross sections where resonances are not present, and individual fine structure levels can be correctly matched spectroscopically, though resonances are neglected in the RDW. To ensure completeness, a high energy range up to 500 Ry above the ionization threshold for each level is considered. Interestingly, the hydrogenic Kramer's approximation also shows the same energy behavior as the RDW. Grouping separately, the BPRM configurations consist of 454 bound levels with resonances corresponding to configurations $1s^22s^22p^4nln'l'$ (n $\leq$ 3, n' $\leq$ 10); including RDW configurations there are 51,558 levels in total. The topup contribution results in $\sim$20\% increment, in addition to the 35\% enhancement from BPRM calculations over the Opacity Project value for the Rosseland Mean Opacity at the Z-temperature of 2.11 $\times 10^6$K (Pradhan and Nahar 2017).