Metallicities, relative ages, and kinematics of stellar populations in ω Centauri

We present results of an extensive spectroscopic survey of subgiant stars in the stellar system omega Cen. Using infrared Ca II 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 subgiant branch (SGB-a), has a metallicity of [Fe/H] similar to -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 the choice of helium abundance. These results impose severe constraints on the timescale 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 metal-intermediate populations are kinematically cooler than the others.