  We have developed a model atom for Cu with which we perform statistical
equilibrium computations that allow us to compute the line formation of Cu I
lines in stellar atmospheres without assuming Local Thermodynamic Equilibrium
(LTE). We validate this model atom by reproducing the observed line profiles of
the Sun, Procyon and eleven metal-poor stars. Our sample of stars includes both
dwarfs and giants. Over a wide range of stellar parameters we obtain excellent
agreement among different Cu I lines. The eleven metal-poor stars have iron
abundances in the range -4.2 <= [Fe/H] <= -1.4, the weighted mean of the
[Cu/Fe] ratios is -0.22 dex, with a scatter of -0.15 dex. This is very
different from the results from LTE analysis (the difference between NLTE and
LTE abundances reaches 1 dex) and in spite of the small size of our sample it
prompts for a revision of the Galactic evolution of Cu.

Solar and Stellar Astrophysics;Astrophysics of Galaxies