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Published online by Cambridge University Press: 26 May 2016
We study the ionization equilibrium of Fe using photoionization models that incorporate improved values for the relevant atomic data. The previously available photoionization models predict concentrations of Fe3+ which are a factor of 3-8 higher than the values inferred from emission lines of [Fe III] and [Fe IV]. Our new models reduce these discrepancies to factors of 2-5. We comment on the possible reasons behind the remaining discrepancies, and present an updated ionization correction factor for obtaining the Fe abundance from the Fe++ abundance.