FE(III) EMISSION-LINES IN THE OPTICAL-SPECTRUM OF THE PLANETARY-NEBULA IC-4997

Relative populations for the 17 fine-structure levels in the 5D, 3P, H -3, 3F, and 3G States of the 3d6 configuration in Fe III, calculated u sing electron impact excitation rates derived with the R-matrix code, are used to derive theoretical electron temperature and density sensit ive emission-line ratios applicable to the spectra of astronomical obj ects in the 4607-5412 angstrom wavelength range. A comparison of these with high spectral resolution observational data for the planetary ne bula IC 4997 reveals generally good agreement between theory and obser vation. This provides experimental support for the accuracy of the the oretical ratios, and illustrates their usefulness in determining plasm a parameters for the Fe III emitting region of a gaseous nebula.