Iron ion abundances (computed with XSTAR) as a function of log(ξ) for an optically thin slab and assuming either an NLSy1 (top) or a powerlaw (bottom) incident SED. Dark to light colours correspond to the increasing ionic charge, with the lightest (and rightmost) line being Fe XXVII. Dashed vertical lines in the top and bottom panels correspond, respectively, to the input and best-fit values (see text).