Perez-Montero, E., Amorin, R., Perez-Diaz, B., Vilchez, J. M., Garcia-Benito, R.2024-11-272024-11-272023/03/020035-8711http://dx.doi.org/10.1093/mnras/stad621https://publicacionesabiertas.userena.cl/handle/123456789/101We present an adapted version of the code HII-CHI-mistry-UV to derive chemical abundances from emission lines in the ultraviolet, for use in narrow line regions (NLR) of active galactic nuclei (AGN). We evaluate different ultraviolet emission line ratios and how different assumptions about the models, including the presence of dust grains, the shape of the incident spectral energy distribution, or the thickness of the gas envelope around the central source, may affect the final estimates as a function of the set of emission lines used. We compare our results with other published recipes for deriving abundances using the same emission lines and show that deriving the carbon-to-oxygen abundance ratio using C iii] lambda 1909 angstrom and O iii] lambda 1665 angstrom emission lines is a robust indicator of the metal content in AGN that is nearly independent of the model assumptions, similar to the case of star-forming regions. Moreover, we show that a prior determination of C/O allows for a much more precise determination of the total oxygen abundance using carbon UV lines, as opposed to assuming an arbitrary relationship between O/H and C/O, which can lead to non-negligible discrepancies.REDSHIFT RADIO GALAXIES, MASS-METALLICITY RELATION, REST-FRAME ULTRAVIOLET, ACTIVE GALACTIC NUCLEI, STAR-FORMING GALAXIES, ULTRA DEEP FIELD, SEYFERT 2 AGNS, CHEMICAL ABUNDANCES, PHOTOIONIZATION MODELS, OPTICAL SPECTROSCOPYArticle