New evidence for the complex structure of the red giant branch in ω Centauri

We report on the complex structure of the red giant branch (RGB) of omega Centauri, based on a new wide-field and wide-color baseline B and I photometry. Our color-magnitude diagram (CMD) shows the presence of multiple populations along this branch; in particular, we discovered an anomalous branch (RGB-a), which appears to be well separated from the bulk of the RGB stars. On the basis of our CMD and from the previous literature, we conclude that (1) these stars, clearly identified as a separate population in our CMD, represent the extreme metal-rich extension ([Ca/H] > -0.3) of the stellar content of omega Cen and show anomalous abundances of s-process elements las Ba and Zr) as well; (2) they are physical members of the omega Cen system; (3) they comprise similar to 5% of the stars of the whole system; and (4) this component and the metal intermediate one (-0.4 > [Ca/H] > -1) have been found to share the same spatial distribution, both of them differing significantly from the most metal-poor one ([Ca/H] < -1). This last piece evidence supports the hypothesis that metal-rich components could belong to an independent (proto?) stellar system captured in the past by omega Cen.