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We present metallicity measurements based on GIRAFFE@VLT spectra of 80 subgiant-branch stars of the Galactic globular cluster ω Centauri. The VLT spectroscopic data are complemented by color-magnitude diagrams from high-accuracy photometry on a ∼ 10 × 10 arcmin 2 mosaic of ACS/HST images centered on the cluster center, and on multicolor images of a ∼ 34×33 arcmin 2 field, taken with the WFI@ESO2.2m camera. Our main purpose was to combine photometric data with spectroscopic data, in the hope of teasing apart some of the population mysteries that neither data set can answer on its own. We have obtained the Fe/H abundance for each of the 80 target stars, and the abundances of C, N, Ca, Ti, and Ba for a subset of them, by comparison with synthetic spectra. We show that stars with Fe/H −1.25 have a large magnitude spread on the flat part of the SGB. We interpret this as empirical evidence for an age spread. A relative age has been obtained for each star, from theoretical isochrones for its metallicity, α-enhancement, and presumed He content. We have identified four distinct stellar groups within the SGB region: (i) an old, metal-poor group (Fe/H ∼ −1.7); (ii) an old, metal-rich group (Fe/H ∼ −1.1); (iii) a young (up to 4–5 Gyr younger than the old component) metal-poor group (Fe/H ∼ −1.7); (iv) a
Villanova et al. (Fri,) studied this question.