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Session 63 - Stars and A Radio Source.
Oral session, Tuesday, January 14
The ionization structure and emission spectra of Fe is ivestigated for a variety of H II regions, including diffuse nebulae, planetary nebulae, and supernova remnants. This work includes: (i) detailed study of ionization, recombination, and excitat ion mechanisms and radiative transfer effects in Fe and Ni ions under nebular conditions; (ii) study of the physical structure and kinematics of nebulae and their ionization fronts; (iii) new atomic data for photoionization, recombination, and excitation of the relevant Fe and Ni ions. It is found that the ionization structure is significantly different from that in previous models, and that the optical [Fe II], [Ni II], and [O I] emission originates from high density, partially ionized shells at the ionization front. Such a dense shell is predicted by hydrodynamic models of the ionization front and is inferred from spectroscopic diagnostics with the optical [Fe II] lines. Expansion velocities of different regions of the Orion nebula also appear to confirm the high densities at the ionization front.
Program listing for Tuesday