Laboratory Measurements of Ca XIX Dielectronic Recombination Satellites

TL;DR

This study provides precise laboratory measurements of Ca XIX dielectronic recombination satellites, validating atomic data used in astrophysical plasma modeling and benchmarking theoretical calculations against experimental results.

Contribution

The paper presents the first high-resolution measurements of Ca XIX dielectronic recombination satellites, confirming theoretical predictions and improving atomic data accuracy for astrophysical applications.

Findings

Measured energies agree with FAC calculations within 0.1%.

Experimental DR rates match OPEN-ADAS data within 10%.

Benchmarking with XRISM spectra confirms the relevance of DR satellites.

Abstract

We report measurements of the K$\alpha$ emission from the astrophysically very abundant Ca XIX (He-like ion) and its satellite lines resonantly excited by dielectronic recombination (DR). We achieve an electron-energy resolution of 8 eV in a cryogenic electron beam ion trap, and determine the energies of the exciting electrons and the emitted photons up to the KLn ($n\le 8$) manifold with $0.05\%$ and $0.1\%$ respective uncertainties. For the KLL satellites, energies agree very well with our predictions using the Flexible Atomic Code (FAC) and previous state-of-the-art calculations. Our calculations also agree with our experimental direct excitation cross-sections for K$\alpha$ within their $10\%$ uncertainty. We extract DR coefficient rates and find good agreement with values tabulated in the OPEN-ADAS database. As an application, we experimentally benchmark Ca XIX atomic data used to model high-temperature astrophysical plasmas by comparing FAC synthetic spectra with recent XRISM observations revealing the contributions of DR satellites to the Ca XIX lines.