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We have obtained high-resolution, high S/N spectra for six red giants in omega Cen: three belonging to the recently discovered, metal-rich Red Giant Branch (RGB-a, Pancino et al. 2000) and three to the metal intermediate population (RGB-MInt). Accurate Iron, Copper and alpha-elements (Ca and Si) abundances have been derived and discussed. In particular, we have obtained the first direct abundance determination based on high-resolution spectroscopy for the RGB-a population, <[Fe/H]>=-0.60+/-0.15. Although this value is lower than previous estimates based on Calcium triplet measurements, we confirm that this population is the most metal rich in omega Cen. In addition, we have found a significant difference in the alpha-elements enhancement of the two populations. The three RGB-MInt stars have the expected overabundance, typical of halo and globular clusters stars: <[alpha/Fe]>=+0.29+/-0.01. The three RGB-a stars show, instead, a significantly lower alpha-enhancement: <[alpha/Fe]>=+0.10+/-0.04. We have also detected an increasing trend of [Cu/Fe] with metallicity, similar to the one observed for field stars by Sneden et al. (1991). The observational facts presented in this letter, if confirmed by larger samples of giants, are the first indication that supernovae type Ia ejecta have contaminated the medium from which the metal rich RGB-a stars have formed. The implications for current scenarios on the formation and evolution of omega Cen are briefly discussed.
We analyze spectra of 18 stars belonging to the faintest subgiant branch in omega Centauri (the SGB-a), obtained with GIRAFFE@VLT at a resolution o R~17000 and a S/N ratio between 25 and 50. We measure abundances of Al, Ba, Ca, Fe, Ni, Si, and Ti and
High-resolution optical spectra are analyzed for two of the four metal rich mildly hydrogen-poor or helium-enhanced giants discovered by Hema and Pandey (2014) along with their comparison normal (hydrogen-rich) giants of Omega Cen. The strengths of t
The helium-enriched (He-enriched) metal-rich red giants of Omega Centauri, discovered by Hema and Pandey using the low-resolution spectra from the Vainu Bappu Telescope (VBT) and confirmed by the analyses of the high-resolution spectra obtained from
We use numerical N-body hydrodynamical simulations with varying PopIII stellar models to investigate the possibility of detecting first star signatures with observations of high-redshift damped Ly$alpha$ absorbers (DLAs). The simulations include atom
We adopted uvby Stroemgren photometry to investigate the metallicity distribution of Omega Cen Red Giant (RG) stars. We provided a new empirical calibration of the Stroemgren m1 = (v-b)-(b-y) metallicity index based on cluster stars. The new calibrat