X-ray spectra of the Fe-L complex

There has been a growing request from the X-ray astronomy community for quantitative estimate of systematic uncertainties originating atomic data used in plasma codes. Though there have several studies looking into using theoretical calculations, general, is no commonly accepted solution this task. We present new approach estimating line emissivities current models collisional plasma, mainly based upon dedicated analysis observed high resolution spectra stellar coronae and galaxy clusters. find that lines consistently show anti-correlation with model fluxes, after properly accounting additional ion concentration calculation. The strong are general better reproduced, indicating modeling main transitions more accurate than those minor ones. This underlying found to be roughly independent on source properties, positions, species, formation processes. further apply our method simulated XRISM Athena observations sources discuss impact interpretation these spectra. typical 1-2% temperature 3-20% abundances O, Ne, Fe, Mg, Ni.