Hubble Space Telescope Observations of an Outer Field in Omega Centauri: A Definitive Helium Abundance

King, I. R.; Bedin, L. R.; Cassisi, S.; Milone, A. P.; Bellini, A.; Piotto, G.; Anderson, J.; Pietrinferni, A.; Cordier, D.
Bibliographical reference

The Astronomical Journal, Volume 144, Issue 1, article id. 5 (2012).

Advertised on:
7
2012
Number of authors
9
IAC number of authors
1
Citations
73
Refereed citations
67
Description
We revisit the problem of the split main sequence (MS) of the globular cluster ω Centauri, and report the results of two-epoch Hubble Space Telescope observations of an outer field, for which proper motions give us a pure sample of cluster members, and an improved separation of the two branches of the MS. Using a new set of stellar models covering a grid of values of helium and metallicity, we find that the best possible estimate of the helium abundance of the bluer branch of the MS is Y = 0.39 ± 0.02. For the cluster center, we apply new techniques to old observations: we use indices of photometric quality to select a high-quality sample of stars, which we also correct for differential reddening. We then superpose the color-magnitude diagram of the outer field on that of the cluster center, and suggest a connection of the bluer branch of the MS with one of the more prominent among the many sequences in the subgiant region. We also report a group of undoubted cluster members that are well to the red of the lower MS. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555.
Related projects
NGC 2808 Globular Cluster
Milky Way and Nearby Galaxies
The general aim of the project is to research the structure, evolutionary history and formation of galaxies through the study of their resolved stellar populations, both from photometry and spectroscopy. The group research concentrates in the most nearby objects, namely the Local Group galaxies including the Milky Way and M33 under the hypothesis
Martín
López Corredoira