  The copper abundances of 29 metal-poor stars are determined based on the high
resolution, high signal-to-noise ratio spectra from the UVES spectragraph at
the ESO VLT telescope. Our sample consists of the stars of the Galactic halo,
thick- and thin-disk with [Fe/H] ranging from ~ -3.2 to ~ 0.0 dex. The
non-local thermodynamic equilibrium (NLTE) effects of Cu I lines are
investigated, and line formation calculations are presented for an atomic model
of copper including 97 terms and 1089 line transitions. We adopted the recently
calculated photo-ionization cross-sections of Cu I, and investigated the
hydrogen collision by comparing the theoretical and observed line profiles of
our sample stars. The copper abundances are derived for both local
thermodynamic equilibrium (LTE) and NLTE based on the spectrum synthesis
methods. Our results show that the NLTE effects for Cu I lines are important
for metal-poor stars, in particular for very metal-poor stars, and these
effects depend on the metallicity. For very metal-poor stars, the NLTE
abundance correction reaches as large as ~ +0.5 dex compared to standard LTE
calculations. Our results indicate that [Cu/Fe] is under-abundant for
metal-poor stars (~ -0.5 dex) when the NLTE effects are included.
