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Omega Centauri is a peculiar Globular Cluster formed by a complex stellarpopulation. To shed light on this, we studied 172 stars belonging to the 5 SGBsthat we can identify in our photometry, in order to measure their [Fe/H]content as well as estimate their age dispersion and the age-metallicityrelation. The first important result is that all of these SGBs has adistribution in metallicity with a spread that exceeds the observational errorsand typically displays several peaks that indicate the presence of severalsub-populations. We were able to identified at least 6 of them based on theirmean [Fe/H] content. These metallicity-based sub-populations are seen tovarying extents in each of the 5 SGBs. Taking advantage of the age-sensitivityof the SGB we showed that, first of all, at least half of the sub-populationshave an age spread of at least 2 Gyrs. Then we obtained an age-metallicityrelation that is the most complete up to date for this cluster. Theinterpretation of the age-metallicity relation is not straightforward, but itis possible that the cluster (or what we can call its progenitor) was initiallycomposed of two populations having different metallicities. Because of theirage, it is very unlikely that the most metal-rich derives from the mostmetal-poor by some kind of chemical evolution process, so they must be assumedas two independent primordial objects or perhaps two separate parts of a singlelarger object, that merged in the past to form the present-day cluster.

The metallicity spread and the age-metallicity relation of Omega Centauri