Upgrading electron temperature and electron density diagnostic diagrams of forbidden line emission (Research Note)

Context. Diagnostic diagrams of forbidden lines have been a useful tool for observers for many decades now. They are used to obtain information on the basic physical properties of thin gaseous nebulae. Some diagnostic diagrams are in wavelength domains that were difficult to apply either due to missing wavelength coverage or the low resolution of older spectrographs. Furthermore, most of the diagrams were calculated using just the species involved as a single atom gas, although several are affected by well-known fluorescence mechanisms as well. Additionally, the atomic data have improved up to the present time. Aims. The aim of this work is to recalculate well-known, but also sparsely used, unnoted diagnostics diagrams. The new diagrams provide observers with modern, easy-to-use recipes for determining electron temperature and densities. Methods. The new diagnostic diagrams were calculated using large grids of parameter space in the photoionization code CLOUDY. For a given basic parameter (e. g., electron density or temperature), the solutions with cooling-heating-equilibrium were chosen to derive the diagnostic diagrams. Empirical numerical functions were fitted to provide formulas usable in, e. g., data reduction pipelines. Results. The resulting diagrams differ significantly from those used up to now and will improve thermodynamic calculations. To our knowledge, detailed, directly applicable fit formulas are given for the first time, leading to the calculation of electron temperature or density from the line ratios.