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.

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Hubble Space Telescope observations of an outer field in omega Centauri: A definitive helium abundance

机译：Hubble Space Telescope observations of an outer field in omega Centauri: A definitive helium abundance

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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.

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《The Astronomical journal》 |2012年第1期|5-1-5-11|共11页
作者
King I.R.; Bedin L.R.; Cassisi S.Milone A.P.Bellini A.Piotto G.Anderson J.Pietrinferni A.Cordier D.;
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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, ItalyInstituto de Astrofìsica de Canarias, E-38200 La Laguna, Tenerife, Canary Islands, SpainDipartimento di Astronomia, Università di Padova, Vicolo dell'Osservatorio 2, I-35122 Padova, ItalyInstitut UTINAM, Observatoire de Besan?on-UMR CNRS 6213, 41 bis avenue de lObservatoire, F-25000 Besan?on, France;

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正文语种英语
中图分类天文学;
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globular clusters: individual (NGC 5139); Hertzsprung-Russell and C-M diagram; proper motions; stars: abundances; stars: Population II;

Hubble Space Telescope observations of an outer field in omega Centauri: A definitive helium abundance

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