The Chemical Inhomogeneity of Omega Centauri

Freeman, K. C.; Rodgers, A. W.

doi:10.1086/181945

Cited by 153 publications

(118 citation statements)

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“…13, the iron abundances are also well correlated with calcium abundances, and the Ca content correlates with the s-process element abundance. A similar behavior is again present in ω Centauri, where a spread in Ca was first detected by Freeman & Rodgers (1975). Villanova et al (2007) showed that the SGB population with [Fe/H] ∼ -1.2 has a mean [Ca/Fe] that is higher by ∼0.1 dex, than that found for the more metal-poor population.…”

Section: The Spread In Fe Of M 22supporting

confidence: 64%

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A double stellar generation in the globular cluster NGC 6656 (M 22)

Marino

Milone

Piotto

et al. 2009

A&A

262

383

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We present a chemical abundance analysis based on high resolution UVES spectra of seventeen bright giant stars in the Globular Cluster (GC) M 22. We obtained an average iron abundance of [Fe/H] = −1.76 ± 0.02 (internal errors only) and an α enhancement of 0.36 ± 0.04 (internal errors only). Na and O, and Al and O follow the well known anticorrelations found in many other GCs. We identified two groups of stars with significantly different abundances of the s-process elements Y, Zr, and Ba. The relative numbers of the two group members are very similar to the ratio of the number of stars in the two sub giant branches (SGB) of M 22. Y and Ba abundances do not correlate with Na, O, and Al. The s-element rich stars are also richer in iron and have higher Ca abundances. The results from high resolution spectra were confirmed by analyses of lower resolution GIRAFFE spectra of fourteen additional M 22 stars. The analyses of the GIRAFFE spectra also show that the Eu -a pure r-process element -abundance is not related to the iron content. We discuss the chemical abundance pattern of M 22 stars in the context of GC multiple stellar populations phenomenon.

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Section: The Spread In Fe Of M 22supporting

confidence: 64%

“…This object is the only one for which variations in iron-peak elements have been reliably identified (Freeman & Rodgers 1975;Norris et al 1996;Suntzeff & Kraft 1996). The Fe multimodal distribution is at least in part responsible for the multiple RGB (Lee et al 1999;Pancino et al 2000) of ω Cen.…”

Section: Introductionmentioning

confidence: 91%

A double stellar generation in the globular cluster NGC 6656 (M 22)

Marino

Milone

Piotto

et al. 2009

A&A

262

383

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“…For four decades, only one GC-like system, namely ω Centauri, was known to display an intrinsic dispersion in Fe (see e.g. Freeman & Rodgers 1975;Norris & Da Costa 1995;Origlia et al 2003;Johnson & Pilachowski 2010;Pancino et al 2011) and this evidence brought to classify the system as the remnant core of a tidally disrupted dwarf galaxy accreted by the Milky Way. In the last few years, deep and extensive spectroscopic and photometric investigations have revealed a more complex picture, with the discovery of other (massive) GCs harboring distinct sub-populations with different iron abundance, as Terzan 5 (Ferraro et al 2009;Origlia et al 2011Origlia et al , 2013Massari et al 2014) and M2 (Yong et al 2014), or with large but uni-modal iron distributions, as M54 (Carretta et al 2010a) and M22 (Marino et al 2009).…”

Section: Introductionmentioning

confidence: 99%

The Origin of the Spurious Iron Spread in the Globular Cluster NGC 3201

Mucciarelli

Lapenna

Massari

et al. 2015

ApJ

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NGC 3201 is a globular cluster suspected to have an intrinsic spread in the iron content. We re-analysed a sample of 21 cluster stars observed with UVES-FLAMES at the Very Large Telescope and for which Simmerer et al. found a 0.4 dex wide [Fe/H] distribution with a metal-poor tail. We confirmed that when spectroscopic gravities are adopted, the derived [Fe/H] distribution spans ∼0.4 dex. On the other hand, when photometric gravities are used, the metallicity distribution from Fe I lines remains large, while that derived from Fe II lines is narrow and compatible with no iron spread. We demonstrate that the metal-poor component claimed by Simmerer et al. is composed by asymptotic giant branch stars that could be affected by non local thermodynamical equilibrium effects driven by iron overionization. This leads to a decrease of the Fe I abundance, while leaving the Fe II abundance unaltered. A similar finding has been already found in asymptotic giant branch stars of the globular clusters M5 and 47 Tucanae. We conclude that NGC 3201 is a normal cluster, with no evidence of intrinsic iron spread.

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“…These molecular line strength variations are driven by star-to-star abundance variations for the light elements from C to Al (see reviews by Kraft 1994and Gratton et al 2004, 2012a for details.) Secondly, a star-to-star dispersion in iron-peak elements, and other elements, has long been known to exist in the globular cluster ω Centauri (e.g., Freeman & Rodgers 1975;Cohen 1981;Norris & Da Costa 1995;Smith et al 2000;Johnson & Pilachowski 2010). More recently, abundance dispersions have also been identified in a number of globular clusters including M2 , M22 (Marino et al 2009Roederer et al 2011), M54 (Carretta et al 2010a) Carretta et al 2011), NGC 3201 1 (Simmerer et al 2013), NGC 5824 2 ) and Terzan 5 (Ferraro et al 2009;Origlia et al 2013), although the shape of the metallicity distribution function differs between these objects.…”

Section: Introductionmentioning

confidence: 99%

CNO abundances in the globular clusters NGC 1851 and NGC 6752★

Yong¹,

Grundahl²,

Norris³

2014

Monthly Notices of the Royal Astronomical Society

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We measure the C+N+O abundance sum in red giant stars in two Galactic globular clusters, NGC 1851 and NGC 6752. NGC 1851 has a split subgiant branch which could be due to different ages or C+N+O content while NGC 6752 is representative of the least complex globular clusters. For NGC 1851 and NGC 6752, we obtain average values of A(C+N+O) = 8.16 ± 0.10 (σ = 0.34) and 7.62 ± 0.02 (σ = 0.06), respectively. When taking into account the measurement errors, we find a constant C+N+O abundance sum in NGC 6752. The C+N+O abundance dispersion is only 0.06 dex, and such a result requires that the source of the light element abundance variations does not increase the C+N+O sum in this cluster. For NGC 1851, we confirm a large spread in C+N+O. In this cluster, the anomalous RGB has a higher C+N+O content than the canonical RGB by a factor of four (∼0.6 dex). This result lends further support to the idea that the two subgiant branches in NGC 1851 are roughly coeval, but with different CNO abundances.

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The Chemical Inhomogeneity of Omega Centauri

Cited by 153 publications

References 0 publications

A double stellar generation in the globular cluster NGC 6656 (M 22)

A double stellar generation in the globular cluster NGC 6656 (M 22)

The Origin of the Spurious Iron Spread in the Globular Cluster NGC 3201

CNO abundances in the globular clusters NGC 1851 and NGC 6752★

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