Theoretical models for H II regions. I - Diagnostic diagrams

Abstract

Systematic modelling techniques employing the latest atomic data are used to compute a comprehensive grid of model H II regions, covering a wide range of physical conditions and comprising a total of 211 independent models. Theoretical diagnostic diagrams for the H II regions are constructed, and it is shown that these diagrams can be employed to determine the metallicity and ionization parameter of an observed H II region and the ionization temperature of the exciting star or stars. To check the modelling procedure, theoretical loci for H II regions are generated on the three principal excitation diagrams of Baldwin, Phillips, and Terlevich (1981), and it is demonstrated that the theoretical models agree with the observed positions of H II regions on these diagrams.