The 2017 release of CLOUDY

TLDR: The 2017 version of Cloudy as mentioned in this paper is the most recent version of the spectral synthesis code, which has made many improvements to the scope and accuracy of the physics which have been made since the previous release.

Abstract: We describe the 2017 release of the spectral synthesis code Cloudy , summa- rizing the many improvements to the scope and accuracy of the physics which have been made since the previous release. Exporting the atomic data into external data files has enabled many new large datasets to be incorporated into the code. The use of the complete datasets is not realistic for most calculations, so we describe the lim- ited subset of data used by default, which predicts significantly more lines than the previous release of Cloudy . This version is nevertheless faster than the previous release, as a result of code optimizations. We give examples of the accuracy limits using small models, and the performance requirements of large complete models. We summarize several advances in the H- and He-like iso-electronic sequences and use our complete collisional-radiative models to establish the densities where the coronal and local thermodynamic equilibrium approximations work.