The origin of Fe II and [Fe II] emission lines in the 4000-10000 Å range in the BD Weigelt blobs of η Carinae

We present numerical simulations that reproduce the salient features of the amazingly strong [Fe II] and Fe II emission spectra in the B and D Weigelt blobs of Carinae. For our studies we have used spectra obtained during the 1998 epoch observations with the Hubble Space Telescope (HST). The spectrum of the B and D Weigelt blobs dominates in [Fe II] and Fe II emission lines. The same observations show no Fe I or Fe III We have compared our measurements of the strongest (greater than or equal to200) [Fe II] and Fe II lines and blends in the spectrum 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 of the spectrum on electron density, pumping by the blackbody-like stellar continuum, and intense Lyalpha emission. We find that radiative pumping is essential in explaining the observed spectrum. We have identified the main pumping routes responsible for the observed Fe II emission. Comparison between the model and observations reveals details of the radiation field. Pumping by the blackbody-like stellar radiation field from eta Carinae explains the numerous strong [Fe II] and Fe II lines in the range of 4000-6500 Angstrom. The strongest Fe II lines in a range of 8000-10000 Angstrom are pumped by intense Lyalpha radiation.