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J. A. Simmerer, I.I. Ivans, C. Sneden (University of Texas Austin), R. P. Kraft (UCO/Lick Observatory)
While many Galactic abundance trends are reasonably well understood and modeled, the nucleosynthetic origin of copper is still something of a mystery. Sneden et al. (1991) found that in field stars the abundance ratio [Cu/M] declines sharply with decreasing metallicity: at [Fe/H] ~ -1, [Ce/Fe] ~ -0.2; at [Fe/H] ~ -3, [Cu/Fe] ~ -1. They also included in their study an analysis of Cu abundances for several globular cluster stars and a reanalysis of previously published results for population I stars. They found this abundance trend throughout the entire sample. In contrast, in the massive multi-metallicity globular cluster Omega Centauri Smith et al. (2000) found no trend at all in [Cu/Fe] with [Fe/H]. Instead, [Cu/Fe] ~ -0.6 over the range -2 < [Fe/H] < -0.9 .
In an effort to better understand Cu trends, we will present the Cu abundances of stars in other selected globular clusters. This sample includes high and medium resolution (R ~ 60,000 and 30,000, respectively), high S/N spectra of approximately 16 stars from M5 and 18 stars from M4. Stellar metallicities in the two clusters M4 and M5 are comparable, but our preliminary results indicate that [Cu/Fe] ~ -0.25 in M4 and [Cu/Fe] ~ -0.6 in M5.