Presentation #318.01 in the session Computation, Data Handling, Image Analysis II.
Next-generation microcalorimeter missions like XRISM and Athena will revolutionize X-ray spectroscopy by offering a plethora of high-resolution X-ray spectra. Interpreting these observations requires a complete understanding of how matter interacts with light through such microphysical processes as absorption and excitation. I developed a framework describing the atomic processes for both collisionally-ionized and photoionized plasmas over a wide range of column densities. Through various line-intensity and line-ratio spectral diagnostics, I established four asymptotic limits; Cases A, B, C, and D. These apply to the formation of lines in H- and He-like systems. This is the first work describing these limits in the X-ray regime. I discussed line optical depth effects in H- and He-like iron with applications to the Hitomi observations of hot gas in the Perseus cluster of galaxies. I introduced a novel method of measuring column density using the Case A to B (optically thin to thick) transition by comparing the observed spectra by Hitomi with spectra simulated with the spectral synthesis code CLOUDY. I explored the effects of Li-like iron on the Fe XXV Kα line intensities through Resonant Auger Destruction (RAD) and line broadening effects by electron scattering. These methods are now in place and will be available to the community by the launch of the XRISM mission.