Faint Emission Lines in the Spectrum of the Orion Nebula and the Abundances of Some of the Rarer Elements

Measurements of the emission lines, down to a faint level, in one bright region near the Trapezium in the Orion Nebula, are reported. Most of their measured intensities, corrected for interstellar extinction, agree relatively well with the recombination-line theory. The measured collisionally excited lines yield T of 9000 K, and Ne of 4000 cu cm as the one-point representative model. Relative abundances of He, N, O, Ne, S, Cl, Ar, Fe, and Ni are determined. They show that Fe and Ni are depleted by about a factor of 5 with respect to the other ions, presumably on solid particles that exist even in the strong radiation field and hot ionized gas near the Trapezium. Permitted lines from other elements, mostly resulting from fluorescence, but a few from recombination, are also discussed.