[FE-II] EMISSION FROM HIGH-DENSITY REGIONS IN THE ORION NEBULA

Direct spectroscopic evidence of high-density regions in the Orion Nebula, N(e) almost-equal-to 10(5)-10(7) cm-3, is obtained from the forbidden optical and near-IR [Fe II] emission lines, using new atomic data. Calculations for level populations and line ratios are carried out using 16, 35, and 142 level collisional-radiative models for Fe II. Estimates of Fe+ abundances derived from the near-infrared and the optical line intensities are consistent with a high density of 10(6) cm-3 in the [Fe II] emitting regions. Important consequences for abundance determinations in the nebula are pointed out.