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We checked consistency between the copper abundance derived in six metal-poorstars using UV Cu II lines (which are assumed to form in LTE) and UV Cu I lines(treated in NLTE). Our program stars cover the atmosphere parameters which aretypical for intermediate temperature dwarfs (effective temperature is in therange from approximately 5800 to 6100 K, surface garvity is from 3.6 to 4.5,metallicity is from about -1 to -2.6 dex). We obtained a good agreement betweenabundance from these two sets of the lines, and this testifies aboutreliability of our NLTE copper atomic model. We confirmed that no underabundaceof this element is seen at low metallicities (the mean [Cu/Fe] value is about-0.2 dex, while as it follows from the previous LTE studies copper behaves as asecondary element and [Cu/Fe] ratio in the range of [Fe/H from -2 to -3 dexshould be about -1 dex). According to our NLTE data the copper behaves as aprimary element at low metallicity regime. We also conclude that our new NLTEcopper abundance in metal-poor stars requires significant reconsideration ofthis element yields in the explosive nucleosynthesis.

Copper abundance from Cu I and Cu II lines in metal-poor star spectra: NLTE vs LTE