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The enrichment of Fe relative to α-elements such as O and Mgrepresents a potential means to determine the age of quasars and probethe galaxy formation epoch. To explore how Fe II emission in quasars islinked to physical conditions and abundance, we have constructed an 830level Fe II model atom and investigated through photoionizationcalculations how Fe II emission strengths depend on nonabundancefactors. We have split Fe II emission into three major wavelength bands,Fe II (UV), Fe II (Opt1), and Fe II (Opt2), and explore how the Fe II(UV)/Mg II, Fe II (UV)/Fe II (Opt1), and Fe II (UV)/Fe II (Opt2)emission ratios depend on hydrogen density and ionizing flux in thebroad-line regions (BLRs) of quasars. Our calculations show that (1)similar Fe II (UV)/Mg II ratios can exist over a wide range of physicalconditions, (2) the Fe II (UV)/Fe II (Opt1) and Fe II (UV)/Fe II (Opt2)ratios serve to constrain ionizing luminosity and hydrogen density, and(3) flux measurements of Fe II bands and knowledge of the ionizing fluxprovide tools to derive distances to BLRs in quasars. To derive all BLRphysical parameters with uncertainties, comparisons of our model withobservations of a large quasar sample at low redshift (z<1) aredesirable. The STIS and NICMOS instruments aboard the Hubble SpaceTelescope offer the best means to provide such observations.

Both the Fe II UV emission in the 2000-3000 Å region [Fe II(UV)]and resonance emission line complex of Mg II at 2800 Å areprominent features in quasar spectra. The observed Fe II(UV)/Mg IIemission ratios have been proposed as means to measure the buildup ofthe Fe abundance relative to that of the alpha-elements C, N, O, Ne,and Mg as a function of redshift. The current observed ratios show largescatter and no obvious dependence on redshift. Thus, it remainsunresolved whether a dependence on redshift exists and whether theobserved Fe II(UV)/Mg II ratios represent a real nucleosynthesisdiagnostic. We have used our new 830 level model atom for Fe+in photoionization calculations, reproducing the physical conditions inthe broad-line regions of quasars. This modeling reveals thatinterpretations of high values of Fe II(UV)/Mg II are sensitive not onlyto Fe and Mg abundance, but also to other factors such asmicroturbulence, density, and properties of the radiation field. We findthat the Fe II(UV)/Mg II ratio combined with Fe II(UV)/Fe II(optical)emission ratio, where Fe II(optical) denotes Fe II emission in 4000-6000Å band, can be used as a reliable nucleosynthesis diagnostic forthe Fe/Mg abundance ratios for the physical conditions relevant to thebroad-line regions of quasars. This has extreme importance for quasarobservations with the Hubble Space Telescope and also with the futureJames Webb Space Telescope.

We present numerical simulations that reproduce the salient features of the amazingly strong [Fe ii andFe ii emission spectra in the B and D Weigelt blobs of Carinae. For our studies we have used spectraobtained during the 1998 epoch observations with the Hubble Space Telescope (HST). The spectrum of the Band D Weigelt blobs dominates in [Fe ii and Fe ii emission lines. The same observations show no Fe i orFe iii. We have compared our measurements of the strongest (200) [Fe ii and Fe ii lines and blends in thespectrum with theoretical predictions. Our predictions are based on non-LTE modeling of the Fe ii atom,which includes the lowest 371 energy levels (all levels up to 11.6 eV). We have investigated the dependence ofthe spectrum on electron density, pumping by the blackbody-like stellar continuum, and intense Lyemission. We nd that radiative pumping is essential in explaining the observed spectrum. We have identiedthe main pumping routes responsible for the observed Fe ii emission. Comparison between the model andobservations reveals details of the radiation eld. Pumping by the blackbody-like stellar radiation eld from Carinae explains the numerous strong [Fe ii and Fe ii lines in the range of 40006500 . The strongest Fe iilines in a range of 800010000 are pumped by intense Ly radiation.