Detection of silver in metal-poor stars

The resonance lines of neutral silver appearing at 3280, 3382 Angstrom,in the near-ultraviolet spectral region have been identified on Keck I HIRES spectra of four halo stars with metallicities -1.3 greater than or equal to [Fe/H] greater than or equal to -2.2. This represents the first detection in metal-poor stars of an element in the atomic number range 41 less than or equal to Z less than or equal to 55. The mean relative silver abundance is [[Ag/Fe]] similar or equal to +0.2, with little star-to-star variation. Silver abundance upper limits in three other metal-poor stars are consistent with this mean value. The modest overabundance of silver is similar to the overabundances in this metallicity range exhibited by other neutron-capture elements whose primary nucleosynthesis origin is the r-process (such as europium and dysprosium).