Multiple populations along the asymptotic giant branch of the globular cluster M4

Lardo, C.; Salaris, Maurizio; Savino, A.; Donati, P.; Stetson, P. B.; Cassisi, S.

doi:10.1093/mnras/stw3374

Cited by 24 publications

(29 citation statements)

References 43 publications

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“…The multiple populations in AGB stars in NGC 2808 was also confirmed by Marino et al (2017) who carried out a study combining spectroscopy and photometry. They also looked at NGC 6121 (M4) and found it hosts two main populations in agreement with the finding by Lardo et al (2017) that AGB stars show broadened distribution in close analogy with their RGB counterparts in the C UBI 1 −V diagram. We note, however, that their conclusion on NGC 6121 contradicts the result of MacLean et al (2016) who found that the AGB is populated by Na-poor and O-rich stars (from the analysis of 15 AGB and 106 RGB stars).…”

Section: Introductionsupporting

confidence: 78%

“…Moreover, from the [O/Fe]−[Na/Fe] distribution of the AGB stars studied by Marino et al (2017) we can infer that the Na-rich/O-poor stars account for 47%, which is close to our 2P AGB fraction of 53%. The photometric studies of Marino et al (2017) and Lardo et al (2017) also support the claim that NGC 6121 hosts multiple populations on AGB. Thus we believe that this cluster should have more than one stellar population along its AGB.…”

Section: Fractions Of 1p and 2p Starssupporting

confidence: 62%

“…The errors on T eff and log g could reach ∆T eff ∼ ±260 K and ∆ log g ∼ ±0.12 dex if the reported differential reddening is taken into account at face value, a significant difference from ∆T eff ∼ ±50 K and ∆ log g ∼ ±0.03 dex derived by accounting for only the intrinsic error on the reddening. However, a range of differential reddening values has been proposed for this cluster, for example, from ∼ 0.05 mag by Cudworth & Rees (1990) and ∼ 0.10 mag by Monelli et al (2013); Lardo et al (2017) up to ∼ 0.25 mag by Mucciarelli et al (2011). Considering the complexity and uncertainties in the reddening of NGC 6121, we empirically took the median and decided to consider ∆T eff ∼ ±150 K and ∆ log g ∼ ±0.08 dex as representative of our analytical uncertainties.…”

Section: Observation and Data Reductionmentioning

confidence: 99%

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Sodium abundances of AGB and RGB stars in Galactic globular clusters

Wang

Primas

Charbonnel

et al. 2017

A&A

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Aims. We investigate the Na abundance distribution of asymptotic giant branch (AGB) stars in Galactic globular clusters (GCs) and its possible dependence on GC global properties, especially age and metallicity. Methods. We analyze high-resolution spectra of a large sample of AGB and red giant branch (RGB) stars in the Galactic GCs NGC 104, NGC 6121, and NGC 6809 obtained with FLAMES/GIRAFFE at ESO/VLT, and determine their Na abundances. This is the first time that the AGB stars in NGC 6809 are targeted. Moreover, to investigate the dependence of AGB Na abundance dispersion on GC parameters, we compare the AGB [Na/H] distributions of a total of nine GCs, with five determined by ourselves with homogeneous method and four from literature, covering a wide range of GC parameters. Results. NGC 104 and NGC 6809 have comparable AGB and RGB Na abundance distributions revealed by the K−S test, while NGC 6121 shows a lack of very Na-rich AGB stars. By analyzing all nine GCs, we find that the Na abundances and multiple populations of AGB stars form complex picture. In some GCs, AGB stars have similar Na abundances and/or second-population fractions as their RGB counterparts, while some GCs do not have Na-rich second-population AGB stars, and various cases exist between the two extremes. In addition, the fitted relations between fractions of the AGB second population and GC global parameters show that the AGB second-population fraction slightly anticorrelates with GC central concentration, while no robust dependency can be confirmed with other GC parameters. Conclusions. Current data roughly support the prediction of the fast-rotating massive star (FRMS) scenario. However, considering the weak observational and theoretical trends where scatter and exceptions exist, the fraction of second-population AGB stars can be affected by more than one or two factors, and may even be a result of stochasticity.

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Section: Introductionsupporting

confidence: 78%

Section: Fractions Of 1p and 2p Starssupporting

confidence: 62%

Section: Observation and Data Reductionmentioning

confidence: 99%

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Sodium abundances of AGB and RGB stars in Galactic globular clusters

Wang

Primas

Charbonnel

et al. 2017

A&A

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“…There are at least a few photometric systems currently being used in the study of the MPs in GCs, but, very Lee unfortunately, the definition of MPs in GCs from various photometric studies can differ one from the other (see, e.g., Lardo et al 2011Lardo et al , 2017Lee et al 2009a,b;Lee 2017Lee , 2018Milone et al 2012Milone et al , 2017. The MPs study from broadband photometry tends to rely on the photometric measurements of absorption strengths of some very strong molecular bands, including OH, NH, CN, and CH.…”

Section: Introductionmentioning

confidence: 99%

Multiple Stellar Populations of Globular Clusters from Homogeneous Ca-CN Photometry. IV. Toward Precision Populational Tagging*

Lee¹

2019

ApJ

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Apparently similar but multifaceted photometric systems are currently being used to investigate the multiple stellar populations in globular clusters, without the concrete general agreement on the definition of the multiple populations. In recent years, an attractive idea of utilization of the widely used U BI photometry, C UBI , for the populational tagging of the giant stars in globular clusters has been emerged. We perform a critical analysis of the cn JWL and the C UBI indices, finding that the populational tagging from the C UBI index may not be reliable, due to the inherited trait of the broad-band photometry. As a consequence, the populational number ratios and the cumulative radial distributions from the C UBI index can be easily in error. The results for M3, which shows a very strong radial gradient in the populational number ratio, highlights the strengths of our cn JWL index: both the HST imaging and the ground-based spectroscopy failed to grasp the correct picture, that can be easily achieved with our cn JWL index with small aperture ground-based telescopes, due to the small field of view or crowdedness in the central part of the cluster.

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“…Interestingly, for the two GCs that have been studied more than once so far, conflicting evidence has been reported. In the case of M4 photometric inferences of population proportions (Lardo et al 2017) disagree with the spectroscopic results (MacLean et al 2016). The conflicting spectroscopic evidence for the other case, NGC 6752 (Campbell et al 2013;Lapenna et al 2016) is the topic of the current study.…”

Section: Introductionmentioning

confidence: 73%

NGC 6752 AGB stars revisited

Campbell

MacLean

D’Orazi

et al. 2017

A&A

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Context.A recent study reported a strong apparent depression of Fe i, relative to Fe ii, in the AGB stars of NGC 6752. This depression is much greater than that expected from the neglect of non-local thermodynamic equilibrium effects, in particular the dominant effect of overionisation. The iron abundances derived from Fe i were then used to scale all other neutral species in the study. Aims. Here we attempt to reproduce the apparent Fe discrepancy, and investigate differences in reported sodium abundances. Methods. We compare in detail the methods and results of the recent study with those of an earlier study of NGC 6752 AGB stars. Iron and sodium abundances are derived using Fe i, Fe ii, and Na i lines. We explore various uncertainties to test the robustness of our abundance determinations. Results. We reproduce the large Fe i depression found by the recent study, using different observational data and computational tools. Further investigation shows that the degree of the apparent Fe i depression is strongly dependent on the adopted stellar effective temperature. To minimise uncertainties in Fe i we derive temperatures for each star individually using the infrared flux method (IRFM). We find that the T eff scales used by both the previous studies are cooler, by up to 100 K; such underestimated temperatures amplify the apparent Fe i depression. Our IRFM temperatures result in negligible apparent depression, consistent with theory. We also re-derived sodium abundances and, remarkably, found them to be unaffected by the new temperature scale. [Na/H] in the AGB stars is consistent between all studies. Since Fe is constant, it follows that [Na/Fe] is also consistent between studies, apart from any systematic offsets in Fe. Conclusions. We recommend the use of (V − K) relations for AGB stars, based on comparisons with our individually-derived IRFM temperatures, and their inherently low uncertainties. We plan to investigate the effect of the improved temperature scale on other elements, and re-evaluate the subpopulation distributions on the AGB, in the next paper of this series.

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Multiple populations along the asymptotic giant branch of the globular cluster M4

Cited by 24 publications

References 43 publications

Sodium abundances of AGB and RGB stars in Galactic globular clusters

Sodium abundances of AGB and RGB stars in Galactic globular clusters

Multiple Stellar Populations of Globular Clusters from Homogeneous Ca-CN Photometry. IV. Toward Precision Populational Tagging*

NGC 6752 AGB stars revisited

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