La and Eu abundances in galactic disk and halo stars

From newly-obtained high-resolution, high S/N spectra. the abundances of the elements La and Eu have been determined over the stellar metallicity range -3<[Fe/H]<+0.3 for 159 giant and dwarf stars. In the solar system, La is predominantly made by the s-process, while Eu owes most of its abundance to the r-process. The changing ratio of these elements in stars over a wide metallicity range traces the changing contributions of the two processes to the Galactic abundance mix. Large s-process abundances can be the result of mass transfer from very evolved stars, so to identify these cases we also report carbon abundances in our metal-poor stars. Results indicate that the S-process may be active as early as [Fe/H]=-2.6, though we find some stars at [Fe/H]=-1 that show no strong indication of s-process enrichment. There is a significant spread in the level of s-process enrichment even at solar metallicity. We also find that kinematically distinct stars may also differ in the level of s-process enhancement.