Implications of a mixing origin for globular cluster bimodal CN variations

Smith, Graeme H.; Bell, R. A.

doi:10.1086/114089

Cited by 19 publications

(19 citation statements)

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“…(Bell, Dickens, & Gustafsson 1979;Bell & Dickens 1980;Da Costa & Cottrell 1980;Carbon et al 1982;Trefzger et al 1983;Langer et al 1986;Smith & Suntzeff 1989;Briley et al 1990;Suntzeff & Smith 1991;Brown, Wallerstein, & Oke 1991). Along with these changes, observations of the CN and NH bands have shown that C is anticorrelated with N at all metallicities (Hesser, Hartwick, & McClure 1977;Norris & Freeman 1979;Norris et al 1981;Suntzeff 1981;Langer, Kraft, & Friel 1985;Smith & Bell 1986). Furthermore, N and Na are both anticorrelated with O and their abundances are seen to increase with increasing luminosity Pilachowski 1988;Paltoglou & Norris 1989;Dickens et al 1991;Sneden et al 1991;Drake, Smith, & Suntzeff 1992;Sneden et al 1992;Norris & Da Costa 1995a;Smith et al 1996;Pilachowski et al 1996;hereafter, PSKL96).…”

Section: Introductionmentioning

confidence: 92%

“…Likewise, if mixing reached deeply enough to cause an O vs. N anticorrelation, we would expect to see the 16 O/ 17 O ratio near its equilibrium value between ∼ 50 and 150, depending on the metallicity and luminosity of the model. The observations show C vs. N anticorrelations and 12 C/ 13 C ratios near equilibrium in clusters of all metallicities (see, e.g., Norris 1981;Smith & Norris 1983;Smith & Bell 1986;Pilachowski 1988;Briley et al 1989;Smith & Mateo 1990;Sneden et al 1991;Smith et al 1996;Smith et al 1997), but there is less evidence of O vs. N anticorrelations in the more metal-rich clusters (Dickens et al 1991;Sneden et al 1994;Briley, Smith, & Lambert 1994;Norris & Da Costa 1995a;Briley et al 1997). There is yet no data available for the 16 O/ 17 O ratio in globular cluster stars.…”

Section: Consequences For Mixingmentioning

confidence: 99%

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Proton‐Capture Nucleosynthesis in Globular Cluster Red Giant Stars

Cavallo

Sweigart

Bell

1998

ApJ

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Observational evidence suggests that many of the variations of the surface abundances of light to intermediate mass elements (A < 28) in globular cluster red-giant-branch (RGB) stars can be attributed to non-canonical mixing between the surface and the deep stellar interior during the RGB phase. As a first step to studying this mixing in more detail, we have combined a large nuclear reaction network with four detailed stellar evolutionary sequences of different metallicities in order to follow the production and destruction of the C, N, O, Ne, Na, Mg, and Al isotopes around the hydrogen-burning shell (H shell) of globular cluster RGB stars. The abundance distributions determined by this method allow for the variation in the temperature and density around the H shell as well as for the dependence on both the stellar luminosity and cluster metallicity. Because our nuclear reaction network operates separately from the stellar evolution code, we are able to more readily to explore the effects of the uncertainties in the reaction rates on the calculated abundances.We discuss implications of our results for mixing in the context of the observational data. Our results are qualitatively consistent with the observed C vs. N, O vs. N, Na vs. O, and Al vs. O anticorrelations and their variations -2with both luminosity and metallicity. We see evidence for variations in Na without requiring changes in O, independent of metallicity, as observed by Norris &Da Costa (1995a) andBriley et al. (1997). Also, we derive 12 C/ 13 C ratios near the observed equilibrium value of 4 for all sequences, and predict the temperature-dependent 16 O/ 17 O equilibrium ratio based on new data for the 17 O(p, α) 14 N reaction rate. Additionally, we discuss the Mg isotopic abundances in light of the recent observations of M13 (Shetrone 1996b) and NGC 6752 (Shetrone 1997).

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Section: Introductionmentioning

confidence: 92%

Section: Consequences For Mixingmentioning

confidence: 99%

Proton‐Capture Nucleosynthesis in Globular Cluster Red Giant Stars

Cavallo

Sweigart

Bell

1998

ApJ

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“…Some clusters showed clear bimodalities in CN (or in [N/Fe]) and weaker or missing bimodalities in CH (or in [C/Fe]), while some other clusters instead showed a continuous spread in CN strength. Various studies identified CN bimodalities among red giants of M 3 and M 13 (Suntzeff 1981;Briley et al 2004b), NGC 6752 (Norris et al 1981), ω Cen (Cohen & Bell 1986), NGC 6934 (Smith & Bell 1986), NGC 6171 (Smith 1988), M 71 (Smith & Penny 1989;Lee 2005), M 2 (Smith & Mateo 1990), M 5 (Ramírez & Cohen 2002), NGC 288 and NGC 362 (Kayser et al 2008), NGC 6121 (Marino et al 2008), NGC 6356, and NGC 6528 (Martell & Smith 2009), among others. Bimodalities among MS and sub-giant branch stars have also been found in M 71 (Cohen 1999), 47 Tuc (Cannon et al 1998;Harbeck et al 2003;Briley et al 2004a;Carretta et al 2005), and NGC 6752 .…”

Section: Ch and Cn Bimodalitiesmentioning

confidence: 98%

Low-resolution spectroscopy of main sequence stars belonging to 12 Galactic globular clusters

Pancino

Rejkuba²,

Zoccali

et al. 2010

A&A

164

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Context. Globular clusters show star-to-star abundance variations for light elements that are not yet well understood. The preferred explanation involves a self-enrichment scenario, within which two subsequent generations of stars co-exist in globular clusters. Observations of chemical abundances in the main sequence and sub-giant branch stars allow us to investigate the signature of this chemically processed material without the complicating effects caused by stellar evolution and internal mixing. Aims. Our main goal is to investigate the carbon-nitrogen anti-correlation with low-resolution spectroscopy of 20−50 stars fainter than the first dredge-up in seven Galactic globular clusters (NGC 288, NGC 1851, NGC 5927, NGC 6352, NGC 6388, and Pal 12) with different properties. We complemented our observations with 47 Tuc archival data, with four additional clusters from the literature (M 15, M 22, M 55, NGC 362), and with additional literature data on NGC 288. Methods. In this first paper, we measured the strengh of the CN and CH band indices, which correlate with the N and C abundances, and we investigated the anti-correlation and bimodality of these indices. We compared r CN , the ratio of stars belonging to the CN-strong and weak groups, with 15 different cluster parameters. Results. We clearly see bimodal anti-correlation of the CH and CN band stregths in the metal-rich clusters (Pal 12, 47 Tuc, NGC 6352, NGC 5927). Only M 15 among the metal-poor clusters shows a clearly bimodal anti-correlation. We found weak correlations (sligthly above 1σ) of r CN with the cluster orbital parameters, present-day total mass, cluster concentration, and age. Conclusions. Our findings support the self-enrichment scenario, and suggest that the occurrence of more than two major generations of stars in a GGC should be rare. Small additional generations (<10−20% of the total) would be difficult to detect with our samples. The first generation, which corresponds to the CN-weak stars, usually contains more stars than the second one ( r CN = 0.82 ± 0.29), as opposed to results based on the Na-O anti-correlations.

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“…In The RGB is broadened in the u−g colour from SLOAN photometry (Lardo et al 2011). In NGC 288, NGC 362, NGC 3201, NGC 4590, NGC 5904, NGC 6218, NGC 6254, NGC 6712, NGC 6809, NGC 7099, and NGC 6934 multiple stellar populations are inferred by starto-star light-element abundance variations (Pancino et al 2010;Cohen et al 2005;Carretta et al 2009;Martell et al 2008;Lee et al 2009;Kravtsov et al 2009;Smith & Bell 1986). HST photometry revealed a multiple sequences along the SGB of NGC 362 Piotto et al (2012).…”

Section: Properties Of the Target Clustersmentioning

confidence: 99%

The SUMO project I. A survey of multiple populations in globular clusters

Monelli

Milone

Stetson

et al. 2013

Monthly Notices of the Royal Astronomical Society

144

205

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We present a general overview and the first results of the SUMO project (a SUrvey of Multiple pOpulations in Globular Clusters). The objective of this survey is the study of multiple stellar populations in the largest sample of globular clusters homogeneously analysed to date. To this aim we obtained high signal-to-noise (S/N>50) photometry for main sequence stars with mass down to ∼0.5 M odot in a large sample of clusters using both archival and proprietary U, B, V, and I data from ground-based telescopes. In this paper, we focus on the occurrence of multiple stellar populations in twenty three clusters. We have defined a new photometric index c U,B,I = (U − B) − (B − I), that turns out to be very effective for identifying multiple sequences along the red giant branch (RGB). We found that in the V-c U,B,I diagram all clusters presented in this paper show broadened or multimodal RGBs, with the presence of two or more components. We found a direct connection with the chemical properties of different sequences, that display different abundances of light elements (O, Na, C, N, and Al). The c U,B,I index is also a powerful tool to identify distinct sequences of stars along the horizontal branch and, for the first time in the case of NGC 104 (47 Tuc), along the asymptotic giant branch. Our results demonstrate that i) the presence of more than two stellar populations is a common feature amongst globular clusters, as already highlighted in previous work; ii) multiple sequences with different chemical contents can be easily identified by using standard Johnson photometry obtained with ground-based facilities; iii) in the study of GC multiple stellar populations the c U,B,I index is alternative to spectroscopy, and has the advantage of larger statistics. ⋆ Based on observations made with the INT telescope operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias. Based on observations made with MPG/ESO 2.2m telescope in La Silla, Chile, proposal 088.A-9012.†

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Implications of a mixing origin for globular cluster bimodal CN variations

Cited by 19 publications

References 0 publications

Proton‐Capture Nucleosynthesis in Globular Cluster Red Giant Stars

Proton‐Capture Nucleosynthesis in Globular Cluster Red Giant Stars

Low-resolution spectroscopy of main sequence stars belonging to 12 Galactic globular clusters

The SUMO project I. A survey of multiple populations in globular clusters

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