We present results of an extensive spectroscopic survey of Subgiant stars in
the stellar system omega Centauri. Using infrared CaII triplet lines, we
derived metallicities and radial velocities for more than 250 stars belonging
to different stellar populations of the system. We find that the most metal
rich component, the anomalous Sub Giant Branch (SGB-a), has a metallicity of
[Fe/H] -0.6 fully compatible with that determined along the anomalous Red Giant
Branch (RGB-a). Our analysis suggests that the age of this component and of the
other metal-intermediate (-1.4 < [Fe/H] < -1.0) stellar populations of the
system are all comparable to that of the dominant metal poor population within
2 Gyr regardless of any choice of helium abundance. These results impose severe
constraints on the time-scale of the enrichment process of this stellar system,
excluding the possibility of an extended star formation period. The radial
velocity analysis of the entire sample demonstrates that only the
metal-intermediate populations are kinematically cooler than the others.
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