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Session 7 - Gas and Dust in the ISM.
Display session, Monday, June 10
Great Hall,
We have incorporated a complete radiative-collisional model of the 371 lowest levels of Fe \sc II into the radiative equilibrium code Cloudy. This simulation predicts transitions producing 68,635 lines. The atomic data were taken from the results of the "Iron Project" and recent laboratory spectroscopy; for unknown lines, we use interpolations and øverline g-approximation. A variety of processes affects the Fe \sc II spectrum, including collisional excitation, pumping by the attenuated incident continuum and all \sim 10^4 emission lines included in the calculation, and fluorescence due to overlapping Fe \sc II lines. This allows us to determine local level populations for the Fe \sc II model self-consistently with electron temperature and density within each zone. The Orion Nebula model presented by Baldwin et al. (1991, ApJ, 374, 580; depleted elements, grains, ionization by the central star, and a hydrostatic blister) was recomputed with the large Fe \sc II model. This H \sc II region model, proposed some time ago to reproduce higher ionization optical lines, reproduces the observed Fe \sc II spectrum quite well.
