CHEMICAL ABUNDANCES FOR 855 GIANTS IN THE GLOBULAR CLUSTER OMEGA CENTAURI (NGC 5139)

By Christian I. Johnson, C. Pilachowski. 2010

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We present elemental abundances for 855 red giant branch (RGB) stars in the globular cluster Omega Centauri (ω Cen) from spectra obtained with the Blanco 4 m telescope and Hydra multifiber spectrograph. The sample includes nearly all RGB stars brighter than V = 13.5 and spans ω Cen's full metallicity range. The heavy α elements (Si, Ca, and Ti) are generally enhanced by ∼+0.3 dex and exhibit a metallicity-dependent morphology that may be attributed to mass and metallicity-dependent Type II supernova (SN) yields. The heavy α and Fe-peak abundances suggest minimal contributions from Type Ia SNe. The light elements (O, Na, and Al) exhibit >0.5 dex abundance dispersions at all metallicities, and a majority of stars with [Fe/H]> − 1.6 have [O/Fe], [Na/Fe], and [Al/Fe] abundances similar to those in monometallic globular clusters, as well as O–Na, O–Al anticorrelations and the Na–Al correlation in all but the most metal-rich stars. A combination of pollution from intermediate-mass asymptotic giant branch stars and in situ mixing may explain the light element abundance patterns. A large fraction (27%) of ω Cen stars are O-poor ([O/Fe] < 0) and are preferentially located within 5′–10′ of the cluster center. The O-poor giants are spatially similar, located in the same metallicity range, and are present in nearly equal proportions to blue main-sequence stars. This suggests that the O-poor giants and blue main-sequence stars may share a common origin. [La/Fe] increases sharply at [Fe/H] ≳ −1.6, and the [La/Eu] ratios indicate that the increase is due to almost pure s-process production.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/eb83e7dec7e012af4558ea7dfd32b2c43a4f066f

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In Astronomy and Astrophysics

1. R. Gratton
2. E. Carretta
3. Jay Anderson
4. A. Bragaglia
5. G. Piotto
6. A. Milone
7. L. Bedin
8. F. D’Antona

Citations in the corpus

• Through thick and thin: kinematic and chemical components in the solar neighbourhood (2010, background): “For example, the metallicity distribution in ωCen peaks at [Fe/H] = −1.7 (Smith 2004) and have distinct elemental abundances (Norris & Da Costa 1995; Johnson & Pilachowski 2010), so it might be useful to seek evidence for a stream in stars of similar metallicity and peculiar abundance ratios when…”
• The Hubble Space Telescope UV Legacy Survey of Galactic globular clusters – IX. The Atlas of multiple stellar populations (2016, background): “…2G stars are indeed known to exist in some clusters (e.g., Sollima et al. 2007; Bellini et al. 2009, 2013; Milone et al. 2012b; Cordero et al. 2014; Johnson & Pilachowski 2010) hence this ratio provides a rough indication of the relative number of stars within the analyzed field of view with…”
• Nuclear star clusters (2009, background): “…clusters in the Milky Way, ωCen has long been suspected to be a former NSC (e.g., Bekki and Freeman 2003), due to its large spread in metallicity (e.g., Norris et al. 1996; Johnson and Pilachowski 2010), and possibly also an age spread of several Gyr (Hilker et al. 2004; Villanova et al. 2014).”
• THE AGES OF 55 GLOBULAR CLUSTERS AS DETERMINED USING AN IMPROVED METHOD ALONG WITH COLOR–MAGNITUDE DIAGRAM CONSTRAINTS, AND THEIR IMPLICATIONS FOR BROADER ISSUES (2013, background): “In fact, this alternative is arguably the favored one given that helium-rich stars in ωCen (see, e.g., Johnson & Pilachowski 2010, Marino et al. 2011) and in NGC 2808 (Bragaglia et al. 2010) have low oxygen, and rather high nitrogen, abundances.]”
• The two metallicity groups of the globular cluster M 22: a chemical perspective (2011, background): “12 of Johnson & Pilachowski 2010).”
• Multiple populations in globular clusters (2012, background): “Carretta et al. (2010b) were the first to demonstrate that the Na-O anticorrelation is more extended at intermediate than at low metallicities in ω Cen and M 54, the two most massive globular clusters in the Milky Way, both showing a large dispersion in iron abundance.”
• The GALAH survey: observational overview and Gaia DR1 companion (2016, result): “Our derived Teff follows exepcted trends, and our derived [Fe/H] values show an overall similarity to the complex morphology described in Johnson & Pilachowski (2010), with the reddest giant branch being the most metal-rich.”