Cloudy is a large-scale spectral synthesis code designed to simulate fully physical conditions within an astronomical plasma and then predict the emitted spectrum. The code is freely available and is widely used in the analysis and interpretation of emission-line spectra.
Calculations were performed with version yy.vr of Cloudy, last described by Ferland et al. (2017), and a citation to https://ui.adsabs.harvard.edu/abs/2017arXiv170510877F