Copper abundances of Galactic bulge red giant stars

The copper abundances are derived from both local thermodynamic equilibrium (LTE) and nonlocal thermodynamic equilibrium (NLTE) with the spectral synthesis method. We find that the NLTE effects for Cu I lines show a clear dependence on metallicity, and they gradually increase with decreasing [Fe/H] for our sample stars.

Our results indicate that the NLTE effects of copper are important not only for metal-poor stars but also for supersolar metal-rich ones and the LTE results underestimate the Cu abundances. We note that the [Cu/Fe] trend of the bulge stars is similar to that of the Galactic disk stars spanning the metallicity range of -1.14<[Fe/H]<0.0dex, and the [Cu/Fe] ratios increase with increasing metallicity when [Fe/H] is from ~-1.2 to ~-0.5 dex, favoring a secondary (metallicity-dependent) production of Cu.