New Evidence for the Complex Structure of the Red Giant Branch in ω Centauri

Abstract

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 (&sqbl0;Ca&solm0;H&sqbr0;>-0.3) of the stellar content of omega Cen and show anomalous abundances of s-process elements (as Ba and Zr) as well; (2) they are physical members of the omega Cen system; (3) they comprise approximately 5% of the stars of the whole system; and (4) this component and the metal intermediate one (-0.4>&sqbl0;Ca&solm0;H&sqbr0;>-1) have been found to share the same spatial distribution, both of them differing significantly from the most metal-poor one (&sqbl0;Ca&solm0;H&sqbr0;<-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.

Commission 37: Star Clusters and Associations: (Amas Stellaires Et Associations)

“…(1999) observed a clear evidence of multiple stellar populations in w Centauri. These results were confirmed by Pancino et al (2000) in a photometric study involving 230,000 stars in this cluster.…”

Stellar populations in ω Centauri: a multivariate analysis

“…Following the suggestion of the referee, we propose rather that this group formed where it presently is located, and, for that same reason, is kinematically colder than the others. Pancino et al (2000) have also found that the metalpoor population is elongated along the east-west (major axis) direction, whereas the two metal-richer populations are elongated in the opposite direction. Hilker & Richtler (2000) note that the metal-richest stars are asymmetrically distributed around the center, with an excess toward the south.…”

The HST large programme on ω Centauri – I. Multiple stellar populations at the bottom of the main sequence probed in NIR–Optical

“…More-recent papers have shown that the MS is even more complex than we had previously imagined and that both the blue and the red MS host stellar subpopulations (e.g., Bellini et al 2010). The complexity of multiple stellar populations in this cluster is further demonstrated by the multiple sub-giant branches (SGBs) and red-giant branches (RGBs) and by the presence of a double white-dwarf cooling sequence (Lee et al 1999;Pancino et al 2000;Sollima et al 2005;Villanova et al 2007;Bellini et al 2010;Milone et al 2017).…”