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E.J. Brugamyer, C. Sneden (U. Texas), J.R. King (STScI), A.M. Boesgaard (U. Hawaii), C.P. Deliyannis (Indiana U.)
We report new determinations of copper abundances for a sample of seven metal-poor (--3.1\geq[Fe/H]\geq--1.6) field stars, using two previously little-used Cu~I resonance lines in the near-UV. These lines, appearing at 3247.6Å\ and 3274.0Å, are easily detected on Keck~I HIRES spectra that were originally obtained to study beryllium abundances in the target stars. In earlier work, copper abundance ratios have been derived for a large group of relatively metal-poor field stars using higher excitation Cu~I lines at 5105Å\ and 5782Å. A large, and possibly linear, decrease in [Cu/Fe] with declining [Fe/H] has been suggested. However, the visible wavelength transitions are usually too weak to be detected in stars having less than ~--2 dex overall metallicity. Copper abundances for these very metal-poor stars must be determined from intrinsically stronger lines, and our study represents the first time the near-UV transitions have been analyzed in their spectra. Isotopic and hyperfine splitting was taken into account in the present analysis, and the [Cu/Fe] ratios in our stars were very low, as expected. However, for stars in our sample, [Cu/Fe] was found always to be ~--1, with little or no trend with [Fe/H]. A larger stellar sample is needed to determine whether a floor in [Cu/Fe] has indeed been reached at low metallicities.