EXCITATION OF [NI-II] AND [FE-II] LINES IN GASEOUS NEBULAE

Forbidden Ni II and Fe II emission in a sample of H II regions, circum stellar nebulae, Seyfert galaxies, and supernova remnants is studied u sing new atomic data. Electron densities and temperatures determined w ith [Ni II], [Fe II], and [O I] indicate considerably different condit ions than those obtained with line ratios of other species. Strong [Fe II] to [O I] and [Fe II] to [Ni II] correlations can be established. Models of electron impact excitation and fluorescence excitation by UV continuum of [Ni II] and [Fe II] lines show that fluorescence of [Fe II] lines may not be important, thus constraining the dominant emittin g region to the high-density partially ionized zones, while for [Ni II ] lines fluorescence excitation from low-density fully ionized zones i n the Orion nebula and circumstellar nebulae could extend the emitting region over that of [Fe II]. Fluorescence excitation of these lines i n supernova remnants seems unimportant. Abundance ratios Fe/O and Ni/F e are estimated for Orion and some supernova remnants. It is found tha t the Fe/O ratios in all cases are within a factor of 2 of the solar v alue. The Ni/Fe ratio in supernova remnants seems to be considerably g reater than solar.