The evolution of copper in the globular cluster ω Centauri

Copper abundances are presented for 40 red giant members of the massive Galactic globular cluster omega Centauri, as well as 15 red giant members of the globular clusters NGC 288, NGC 362, NGC 3201, NGC 6752, and M4 ( NGC 6121). The spectra are of relatively high spectral resolution and signal-to-noise ratio. Using these abundances, plus published literature values for field stars, the abundance trends of [Cu/Fe] are defined as a function of [ Fe/H]. The lowest metallicity stars in omega Cen have [Fe/H] similar to -2.0, with the stars in this sample spanning a range from [Fe/H] similar to -2.0 to 0.8. In the field star sample, [Cu/Fe] rises from about -0.8 at [Fe/H] = -2.5 to about -0.4 at [Fe/H] similar to -1.4 and then rises rapidly to [Cu/Fe] similar to0.0 at [Fe/H] = -1.1. The globular clusters (other than omega Cen) tend to also follow the trend as displayed by the field stars. Unlike the field stars, however, omega Cen displays a constant ratio of [Cu/Fe] similar to -0.5 all the way to [Fe/H] = -0.8. At the metallicity of [Fe/H] = -0.8, the values of [Cu/Fe] in omega Cen fall below the corresponding mean ratio in the field stars by roughly 0.5 dex. If copper is produced primarily in Type Ia supernovae (SNe Ia), as suggested in the literature, the lack of an increase in [Cu/Fe] in omega Cen would suggest very little contribution from SNe Ia to its chemical evolution within the metallicity range from [Fe/H] of -2.0 up to -0.8.