On the discrete nature of the red giant branch of ω Centauri

We report on the results of an extensive Very Large Telescope high-resolution imaging campaign of the central region of the giant globular cluster omega Centauri. More than 100000 stars have been measured in the inner 9 × 9 arcmin2 region of the cluster. On the basis of multiband colour-magnitude diagrams, we confirm the existence of multiple stellar populations along the red giant branch (RGB). Moreover, thanks to the high precision of this data set, we conclude that the RGB does not present a smooth and continuous distribution, but shows a discrete structure: besides the metal-poor and the extreme metal-rich population (anomalous RGB), the existence of three metal intermediate populations is shown.