Emission coefficients for gaseous nebulae: three-level atom approximation

The recent compilation of atomic data by Mendoze (1983) has been used to construct three-level atom formulae for the emission coefficients for [N II], [O I], [O II], [O III], [Ne III], [S II], [S III], and [Ar III] as a function of temperature and density. Equations for determining [O II] and [S II] densities and [N II] and [O III] temperatures are presented also. The formulae generally predict emission coefficients and ratios to within 5 per cent of the five-level atom calculations, so should be of considerable value for analyses of gaseous nebulae spectra. (author)