Agb Sodium Abundances in the Globular Cluster 47 Tucanae (Ngc 104)

Johnson, Christian I.; McDonald, Iain; Pilachowski, Catherine A.; Mateo, Mario; Bailey, John I.; Cordero, María José Aguilar; Zijlstra, A. A.; Crane, Jeffrey D.; Olszewski, Edward W.; Shectman, Stephen; Thompson, I. B.

doi:10.1088/0004-6256/149/2/71

Cited by 58 publications

(69 citation statements)

References 112 publications

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“…In contrast, Johnson et al (2015) find that the AGB population in 47 Tuc (NGC 104) presents a much larger [Na/Fe] dispersion, which is nearly identical to that found on the RGB. This GC is both more metal-rich ([Fe/H] = −0.73, Johnson et al 2015) and younger (11.75 ± 0.25, VandenBerg et al 2013).…”

Section: Comparison With Observations and Conclusionmentioning

confidence: 60%

“…Since the typical error bar for Na abundance determination on the AGB is of the order of 0.14 dex according to Campbell et al (2013), the AGB-RGB difference could be detectable only for the old Galactic GCs of intermediate metallicity. Otherwise, the observed [Na/Fe] dispersion on the AGB would be similar to that found on the RGB, as in NGC 104 (Johnson et al 2015) and NGC 2808 (Wang et al, in prep. ), as discussed in Sect.…”

Section: Theoretical Sodium Spread On the Agb As A Function Of Metallmentioning

confidence: 61%

“…This GC is both more metal-rich ([Fe/H] = −0.73, Johnson et al 2015) and younger (11.75 ± 0.25, VandenBerg et al 2013). It would thus lie to the left of NGC 6752 in the age-Δ[Na/Fe] ini (AGB) plane (Fig.…”

Section: Comparison With Observations and Conclusionmentioning

confidence: 82%

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Evolution of long-lived globular cluster stars

Charbonnel

Chantereau

2016

A&A

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Context. Long-lived stars in globular clusters exhibit chemical peculiarities with respect to their halo counterparts. In particular, sodium-enriched stars are identified as belonging to a second stellar population born from cluster material contaminated by the hydrogen-burning ashes of a first stellar population. Their presence and numbers in different locations of the colour-magnitude diagram provide important constraints on the self-enrichment scenarios. In particular, the ratio of Na-poor to Na-rich stars on the asymptotic giant branch (AGB) has recently been found to vary strongly from cluster to cluster (NGC 6752, 47 Tuc, and NGC 2808), while it is relatively constant on the red giant branch (RGB). Aims. We investigate the impact of both age and metallicity on the theoretical sodium spread along the AGB within the framework of the fast rotating massive star (FRMS) scenario for globular cluster self-enrichment. Methods. We computed evolution models of low-mass stars for four different metallicities ([Fe/H] = −2.2, −1.75, −1.15, −0.5) assuming the initial helium-sodium abundance correlation for second population stars derived from the FRMS models and using mass loss prescriptions on the RGB with two realistic values of the free parameter in the Reimers formula. Results. Based on this grid of models we derive the theoretical critical initial mass for a star born with a given helium, sodium, and metal content that determines whether that star will climb or not the AGB. This allows us to predict the maximum sodium content expected on the AGB for globular clusters as a function of both their metallicity and age. We find that (1) at a given metallicity, younger clusters are expected to host AGB stars exhibiting a larger sodium spread than older clusters and (2) at a given age, higher sodium dispersion along the AGB is predicted in the most metal-poor globular clusters than in the metal-rich ones. We also confirm the strong impact of the mass loss rate in the earlier evolution phases on the Na cut on the AGB: the higher the mass loss, the stronger the trends with age and metallicity. Conclusions. The theoretical trends we obtain provide, in principle, an elegant qualitative explanation to the different sodium spreads that are observed along the AGB in the Galactic globular clusters of different ages and [Fe/H] values. Although it is real, the slope with both age and metallicity is relatively flat, although it steepens when accounting for mass loss variations. Therefore, additional parameters may play a role in inducing cluster to cluster variations, that are difficult to disentangle from existing data.

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Section: Comparison With Observations and Conclusionmentioning

confidence: 60%

Section: Theoretical Sodium Spread On the Agb As A Function Of Metallmentioning

confidence: 61%

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Evolution of long-lived globular cluster stars

Charbonnel

Chantereau

2016

A&A

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“…Theoretical works also emphasize the fact that the number of AGB stars in a given GC strongly depends on the assumptions made on the mass loss in the previous evolution phases Charbonnel & Chantereau 2016;Cassisi et al 2014). Moreover, in the framework of the FRMS scenario, the theoretical Na spread on the AGB phase is a function of both age and metallicity (Charbonnel & Chantereau 2016), and the expected trends can explain the presence of 2P stars found in most of the GCs studied so far, which cover a range in age and iron content (47 Tuc, NGC 2808, M 3, M 5, M 13, M 55, M 2, see Johnson & Pilachowski 2012;García-Hernández et al 2015;Johnson et al 2015;Wang et al II, in prep. ) with the exception of M 62 (Lapenna et al 2015).…”

Section: Asymptotic Giant Branchmentioning

confidence: 79%

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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“…The M2FS fiber system and MSpec spectrograph were configured using the high resolution "Bulge_GC1" setup described in Johnson et al (2015), which produces cross-dispersed spectra spanning approximately 6120-6720 Å. The 1″.…”

Section: Observations and Target Selectionmentioning

confidence: 99%

A Spectroscopic Analysis of the Galactic Globular Cluster NGC 6273 (M19)

Johnson

Rich

Pilachowski

et al. 2015

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129

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A combined effort utilizing spectroscopy and photometry has revealed the existence of a new globular cluster class. These "anomalous" clusters, which we refer to as "iron-complex" clusters, are differentiated from normal clusters by exhibiting large (0.10 dex) intrinsic metallicity dispersions, complex sub-giant branches, and correlated [Fe/H] and s-process enhancements. In order to further investigate this phenomenon, we have measured radial velocities and chemical abundances for red giant branch stars in the massive, but scarcely studied, globular cluster NGC 6273. The velocities and abundances were determined using high resolution (R ∼ 27,000) spectra obtained with the Michigan/ Magellan Fiber System (M2FS) and MSpec spectrograph on the Magellan-Clay 6.5 m telescope at Las Campanas Observatory. We find that NGC 6273 has an average heliocentric radial velocity of +144.49 km s −1 (σ = 9.64 km s

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Agb Sodium Abundances in the Globular Cluster 47 Tucanae (Ngc 104)

Cited by 58 publications

References 112 publications

Evolution of long-lived globular cluster stars

Evolution of long-lived globular cluster stars

Evolution of long-lived globular cluster stars

A Spectroscopic Analysis of the Galactic Globular Cluster NGC 6273 (M19)

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