The systematic uncertainties introduced by atomic data in nebular abundance determinations

Atomic data selection is one important source of systematic uncertainty since there are important variations between the values provided by different authors. We explore the effect of using different atomic data in the determination of physical conditions and chemical abundances in a sample of Galactic planetary nebulae and Hii regions. We find that the available datasets introduce significant differences in the results, especially at densities above 10⁴ cm^-3, where O/H and N/O reach uncertainties higher than a factor of 4.