Charge Exchange Induced X-ray Emission of Fe XXV and Fe XXVI via a Streamlined Model

TL;DR

This paper develops a streamlined quantum defect and Landau-Zener based model to predict charge exchange X-ray emission spectra of highly charged iron ions with various targets, improving understanding of astrophysical X-ray observations.

Contribution

It introduces a new computational approach combining quantum defect methods and cascade modeling to generate detailed charge exchange cross sections for Fe XXV and Fe XXVI.

Findings

The model successfully predicts X-ray spectra consistent with experimental data.

Common l-distribution models are inadequate for high-charge ion charge exchange.

The approach enhances interpretation of astrophysical X-ray observations.

Abstract

Charge exchange is an important process for the modeling of X-ray spectra obtained by the Chandra, XMM-Newton, and Suzaku X-ray observatories, as well as the anticipated Astro-H mission. The understanding of the observed X-ray spectra produced by many astrophysical environments is hindered by the current incompleteness of available atomic and molecular data -- especially for charge exchange. Here, we implement a streamlined program set that applies quantum defect methods and the Landau-Zener theory to generate total, n-resolved, and nlS-resolved cross sections for any given projectile ion/ target charge exchange collision. Using this data in a cascade model for X-ray emission, theoretical spectra for such systems can be predicted. With these techniques, Fe25+ and Fe26+ charge exchange collisions with H, He, H2, N2, H2O, and CO are studied for single electron capture. These systems have been selected as they illustrate computational difficulties for high projectile charges. Further, Fe XXV and Fe XXVI emission lines have been detected in the Galactic center and Galactic ridge. Theoretical X-ray spectra for these collision systems are compared to experimental data generated by an electron beam ion trap study. Several l- distribution models have been tested for Fe25+ and Fe26+ single electron capture. Such analysis suggests that commonly used l-distribution models struggle to accurately reflect the true distribution of electron capture as understood by more advanced theoretical methods.