We’re talking about thermal, collisional/coronal, equilibrium, optically thin plasmas here…probably
Diagnostics and Physical Properties
Temperatures and overall emission levels: DEMs
Densities: line ratios…but also source location via f/i
Abundances: line ratios and line-to-continuum ratios
Local absorption: globally and within individual lines
Signatures of photoionization: fluorescence
Kinematics: line broadening and profile shapes