On the Anomalous Red Giant Branch of the Globular Cluster ω Centauri

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Abstract
We present three different optical and near-infrared (NIR) data sets for evolved stars in the Galactic globular cluster omega Centauri. The comparison between observations and homogeneous sets of stellar isochrones and zero-age horizontal branches provides two reasonable fits. Both of them suggest that the so-called anomalous branch has a metal-intermediate chemical composition (-1.1 <= [Fe/H] <= -0.8) and is located similar to 500 pc beyond the bulk of omega Cen stars. These findings are mainly supported by the shape of the subgiant branch in four different color-magnitude diagrams (CMDs). The most plausible fit requires a higher reddening, E(B - V) = 0.155 versus 0.12, and suggests that the anomalous branch is coeval with the bulk of omega Cen stellar populations to within empirical and theoretical uncertainties. This result is supported by the identification of a sample of faint horizontal-branch (HB) stars that might be connected with the anomalous branch. Circumstantial empirical evidence seems to suggest that the stars in this branch form a clump of stars located beyond the cluster
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