HUBBLE SPACE TELESCOPE OBSERVATIONS OF AN OUTER FIELD IN OMEGA CENTAURI: A DEFINITIVE HELIUM ABUNDANCE
- Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195-1580 (United States)
- Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)
- Osservatorio Astronomico di Teramo, Via Mentore Maggini s.n.c., I-64100 Teramo (Italy)
- Instituto de Astrofisica de Canarias, E-38200 La Laguna, Tenerife, Canary Islands (Spain)
- Dipartimento di Astronomia, Universita di Padova, Vicolo dell'Osservatorio 2, I-35122 Padova (Italy)
- Institut UTINAM, Observatoire de Besancon-UMR CNRS 6213, 41 bis avenue de lObservatoire, F-25000 Besancon (France)
We revisit the problem of the split main sequence (MS) of the globular cluster {omega} 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.
- OSTI ID:
- 22034432
- Journal Information:
- Astronomical Journal (New York, N.Y. Online), Vol. 144, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 1538-3881
- Country of Publication:
- United States
- Language:
- English
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