CNO Abundances of Bright Giants in the Globular Clusters M3 and M13

Smith, Graeme H.; Shetrone, Matthew; Bell, R. A.; Churchill, Christopher W.; Briley, Michael M.

doi:10.1086/118119

Cited by 104 publications

(159 citation statements)

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“…The overall C+N+O content is held constant in the two populations because no He-burning products are included in 2P stars, as predicted by the FRMS models and in agreement with observations (Smith et al 1996;Carretta et al 2005). We assumed a range in the initial mixture for 2P stars that results from the dilution of the H-burning products ejected by 1P FRMS models with intra-cluster pristine gas following the assumptions of Decressin et al (2007a) to reproduce the Li-Na anticorrelation observed in NGC 6752 (see details in Sect.…”

Section: Initial Chemical Compositionsupporting

confidence: 72%

Evolution of long-lived globular cluster stars

Chantereau

Charbonnel

Meynet

2016

A&A

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Context. Globular clusters host multiple populations of long-lived low-mass stars whose origin remains an open question. Several scenarios have been proposed to explain the associated photometric and spectroscopic peculiarities. They differ, for instance, in the maximum helium enrichment they predict for stars of the second population, which these stars can inherit at birth as the result of the internal pollution of the cluster by different types of stars of the first population. Aims. We present the distribution of helium-rich stars in present-day globular clusters as it is expected in the original framework of the fast-rotating massive stars scenario (FRMS) as first-population polluters. We focus on NGC 6752. Methods. We completed a grid of 330 stellar evolution models for globular cluster low-mass stars computed with different initial chemical compositions corresponding to the predictions of the original FRMS scenario for [Fe/H] = −1.75. Starting from the initial helium-sodium relation that allows reproducing the currently observed distribution of sodium in NGC 6752, we deduce the helium distribution expected in that cluster at ages equal to 9 and 13 Gyr. We distinguish the stars that are moderately enriched in helium from those that are very helium-rich (initial helium mass fraction below and above 0.4, respectively), and compare the predictions of the FRMS framework with other scenarios for globular cluster enrichment. Results. The effect of helium enrichment on the stellar lifetime and evolution reduces the total number of very helium-rich stars that remain in the cluster at 9 and 13 Gyr to only 12% and 10%, respectively, from an initial fraction of 21%. Within this age range, most of the stars still burn their hydrogen in their core, which widens the MS band significantly in effective temperature. The fraction of very helium-rich stars drops in the more advanced evolution phases, where the associated spread in effective temperature strongly decreases. These stars even disappear from the horizontal branch and the asymptotic giant branch at 13 Gyr. Conclusions. The helium constraint is no suitable criterion for clearly distinguishing between the scenarios for GC self-enrichment because only few very helium-rich stars are predicted in the investigated framework and because it is difficult to derive the helium content of GC stars observationally. However, the helium constraint indicates some difficulties of the original FRMS scenario that require the exploration of alternatives.

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Section: Initial Chemical Compositionsupporting

confidence: 72%

Evolution of long-lived globular cluster stars

Chantereau

Charbonnel

Meynet

2016

A&A

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“…To reach this conclusion, it is assumed that CN traces the N abundace and CH the C abundance (Smith et al 1996). This is well supported by abundance analysis work based on spectral synthesis, which revealed [C/Fe] and [N/Fe] spreads of up to more than 1 dex (see e.g., Briley et al 2004a,b;Cohen et al 2005).…”

Section: Introductionmentioning

confidence: 82%

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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“…10, with the following changes: we express abundances in terms of log N (X)/N (H) rather than [X/Fe], and we use oxygen abundances from Sneden et al (2004) where available. The results of Smith et al (1996) are reproduced: the abundances of C and O are correlated, the N abundance is anticorrelated with both C and O, and the total abundance C+N+O is nearly constant. These patterns can be explained as the result of CNO-cycle hydrogen burning, which converts carbon (rapidly) and oxygen (slowly) into nitrogen, but leaves the total C+N+O abundance unchanged.…”

Section: Helium Abundancementioning

confidence: 76%

“…9, the measured abundances of vZ 1128 (solid symbols) are compared with those of the sun (short horizon- Smith et al (1996), and the O, Al, Si, Fe, and Ni values are from Sneden et al (2004). The vertical extent of each rectangle represents the star-to-star scatter in the measured abundance (±1σ about Figure 9.…”

Section: Discussionmentioning

confidence: 99%

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FUSE, STIS and Keck spectroscopic analysis of the UV-bright star vZ 1128 in M3 (NGC 5272)

Chayer

Dixon

Fullerton

et al. 2015

Mon. Not. R. Astron. Soc.

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We present a spectral analysis of the UV-bright star vZ 1128 in M3 based on observations with the Far Ultraviolet Spectroscopic Explorer (FUSE), the Space Telescope Imaging Spectrograph (STIS), and the Keck HIRES echelle spectrograph. By fitting the H i, He i, and He ii lines in the Keck spectrum with non-LTE H-He models, we obtain T eff = 36,600 K, log g = 3.95, and log N (He)/N (H) = −0.84. The star's FUSE and STIS spectra show photospheric absorption from C, N, O, Al, Si, P, S, Fe, and Ni. No stellar features from elements beyond the iron peak are observed. Both components of the N v λ1240 doublet exhibit P Cygni profiles, indicating a weak stellar wind, but no other wind features are seen. The star's photospheric abundances appear to have changed little since it left the red giant branch (RGB). Its C, N, O, Al, Si, Fe, and Ni abundances are consistent with published values for the red-giant stars in M3, and the relative abundances of C, N, and O follow the trends seen on the cluster RGB. In particular, its low C abundance suggests that the star left the asymptotic giant branch before the onset of third dredge-up.

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CNO Abundances of Bright Giants in the Globular Clusters M3 and M13

Cited by 104 publications

References 0 publications

Evolution of long-lived globular cluster stars

Evolution of long-lived globular cluster stars

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

FUSE, STIS and Keck spectroscopic analysis of the UV-bright star vZ 1128 in M3 (NGC 5272)

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