SOFTWARE FOR THE ANALYSIS OF EMISSION-LINE NEBULAE

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 line emissivities given appropriate emission-line fluxes, the electron temperature (T-e) and density (N-e). The package is based on the five-level atom program developed by De Robertis et al. (JRASC, 81, 195, 1987), but it includes diagnostics from a,oreater set of ions and emission lines, most particularly those in the satellite ultraviolet that are now observable. Two of the applications make use of a three-zone nebular model. to derive T-e and N-e simultaneously in separate zones of low-, 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.