SIMBAD references

A set of software tools has been developed for the IRAF/STSDAS environment to derive the physical conditions in a low-density (nebular) gas given appropriate diagnostic emission line ratios; and lien emissivities given appropriate emission line fluxes, the electron temperature (T_e) and density (N_e). The package is based on the five-level program developed by De Robertis, Dufour and Hunt (1987), but it includes diagnostics from a greater set of ions and emission lines, most particularly those in the satellite ultraviolet that are now observable. Two fo the applications make use of a 3-zone nebular model to derive T_e and N_3 simultaneously in separate zones of low-, and intermediate-, and high-ionization. These applications are useful for calculating nebular densities and temperatures directly from the traditional diagnostic line ratios, either to provide some reasonable input parameters for a more complicated physical model, or to calculate ionic abundances (or other quantities) within some simplifying assumptions. Examples of the utility of these diagnostics for real nebulae are presented.