Sodium abundances of AGB and RGB stars in Galactic globular clusters

Wang, Y.; Primas, F.; Charbonnel, C.; Swaelmen, M. Van der; Bono, G.; Chantereau, William; Zhao, Gang

doi:10.1051/0004-6361/201730976

Cited by 31 publications

(22 citation statements)

References 135 publications

(202 reference statements)

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“…The mean radial velocity obtained for the cluster members is −16.20 ± 7.36 kms −1 , where its uncertainty represents the standard deviation of the stars that contribute to the calculation of the mean. This is in good agreement with −17.3 ± 9.9 kms −1 (Wang et al 2017) and −17.6 ± 7.2 kms −1 (Dobrovolskas et al 2014). We found only one star for which the final radial velocity was more than 3σ away from the mean value of the cluster, and thus we discarded it from any further analysis as a likely a non-member.…”

Section: Archival Datasupporting

confidence: 86%

Lithium in NGC 2243 and NGC 104

Aoki

Primas

Pasquini

et al. 2021

A&A

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Aims. Our aim was to determine the initial Li content of two clusters of similar metallicity but very different ages, the old open cluster NGC 2243 and the metal-rich globular cluster NGC 104. Methods. We compared the lithium abundances derived for a large sample of stars (from the turn-off to the red giant branch) in each cluster. For NGC 2243 the Li abundances are from the catalogues released by the Gaia-ESO Public Spectroscopic Survey, while for NGC 104 we measured the Li abundance using FLAMES/GIRAFFE spectra, which include archival data and new observations. We took the initial Li of NGC 2243 to be the lithium measured in stars on the hot side of the Li dip. We used the difference between the initial abundances and the post first dredge-up Li values of NGC 2243, and by adding this amount to the post first dredge-up stars of NGC 104 we were able to infer the initial Li of this cluster. Moreover, we compared our observational results to the predictions of theoretical stellar models for the difference between the initial Li abundance and that after the first dredge-up. Results. The initial lithium content of NGC 2243 was found to be A(Li)i = 2.85 ± 0.09 dex by taking the average Li abundance measured from the five hottest stars with the highest lithium abundance. This value is 1.69 dex higher than the lithium abundance derived in post first dredge-up stars. By adding this number to the lithium abundance derived in the post first dredge-up stars in NGC 104, we infer a lower limit of its initial lithium content of A(Li)i = 2.34 ± 0.13 dex. Stellar models predict similar values. Therefore, our result offers important insights for further theoretical developments.

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Section: Archival Datasupporting

confidence: 86%

Lithium in NGC 2243 and NGC 104

Aoki

Primas

Pasquini

et al. 2021

A&A

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“…Almost all old globular clusters (GCs, older than ∼10 Gyr) are composed of multiple stellar populations (MPs). One signature of MPs is stars in GCs are not chemically homogeneous: they exhibit star-to-star variations in different elemental abundances, such as He, C, N, O, Na, Mg, Al, etc (Piotto et al 2007;Yong et al 2008;Carretta et al 2009;di Criscienzo et al 2010;Lardo et al 2012;Wang et al 2017;Pancino et al 2017;Milone et al 2019). The number of chemically enriched stars is comparable to, or greater than normal stars (Carretta et al 2009;Milone et al 2012b;.…”

Section: Introductionmentioning

confidence: 99%

When Does the Onset of Multiple Stellar Populations in Star Clusters Occur? III. No Evidence of Significant Chemical Variations in Main-sequence Stars of NGC 419

Wang

Tang

et al. 2020

ApJ

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Recent studies have revealed that the onset age for the presence of multiple stellar populations (MPs) in star clusters seems to correspond to the disappearance of the extended main-sequence turnoff (eMSTO) in young clusters, a pattern associated with stellar rotations. A speculative suggestion is that MPs might be caused by the magnetic brake, a stellar evolutionary effect linked to the rotation. In this work, we use the young massive cluster NGC 419 as a testbed. We examined if its magnetically baked MS stars would exhibit MPs. Using the deep ultraviolet and visible images observed through the Hubble Space Telescope, combined with a specific color index that is sensitive to the nitrogen (N) abundance, we examined if its late G-and K-type MS stars are affected by N variation. Our analysis reports that the morphology of its GK-type MS is most likely an SSP, and only a negligible probability that indicates a N variation up to 0.4 dex is present. We conclude that there is no significant N variation among its GK-type MS stars. The absence of a significant chemical variation among the late-type MS stars indicates that MPs might not be a specific pattern of magnetically braked stars.

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“…In practice, there should be little to no He-rich stars on the RGB and AGB of the cluster NGC 6752, for which the models of Chantereau et al were tailored. This also naturally explains the lack of Na-rich AGB stars in some GCs (Campbell et al 2013;Wang et al 2016Wang et al , 2017, although observations reveal that the presence of 2P AGB stars can be affected by more than one factor (Wang et al 2017).…”

Section: Introductionmentioning

confidence: 92%

“…Globular clusters (GCs) host multiple populations of stars characterized by different spectroscopic and photometric signatures. Anti-correlations between the abundances of several elements such as C-N, Na-O, and sometimes Mg-Al have been reported at the surface of various types of stars, from the main sequence (MS) to the red giant branch (RGB) and the asymptotic giant branch (AGB; e.g., Cohen 1978;Peterson 1980;Sneden et al 1992;Kraft 1994;Thévenin et al 2001;Gratton et al 2007Gratton et al , 2019Mészáros et al 2015;Carretta 2015Carretta , 2019Johnson et al 2016;Pancino et al 2017;Wang et al 2017;Masseron et al 2019). These differences in chemical composition are thought to explain the various sequences observed in color-magnitude diagrams (CMDs) built with specific filters sensitive to atomic and molecular lines of the elements listed above (e.g., Bedin et al 2004;Piotto et al 2007;Bowman et al 2017;Nardiello et al 2018;Marino et al 2019).…”

Section: Introductionmentioning

confidence: 99%

Maximum helium content of multiple populations in the globular cluster NGC 6752

Martins

Chantereau

Charbonnel

2021

A&A

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Context. Multiple populations in globular clusters are usually explained by the formation of stars out of material with a chemical composition that is polluted to different degrees by the ejecta of short-lived, massive stars. But the nature of the “polluters” remains elusive. Different types of stars have been proposed to account for the observed chemical patterns of multiple populations. Among other things, these differ by the amount of helium they spread in the surrounding medium. Aims. In this study we investigate whether the present-day photometric method used to infer the helium content of multiple populations indeed gives the true value or underestimates it by missing very He-rich, but rare stars. This check is important to discriminate between the different polluter scenarios. We focus on the specific case of NGC 6752. Methods. We compute atmosphere models and synthetic spectra along isochrones produced for this cluster for a very broad range of He abundances covering the predictions of the different scenarios, including the extreme case of the fast-rotating massive star (FRMS) scenario. We use the same abundances in isochrones and atmosphere models to ensure consistency. We calculate synthetic photometry in HST filters best suited to study the helium content. We subsequently build synthetic clusters with various distributions of stars. We finally determine the maximum helium mass fraction of these synthetic clusters using a method similar to that applied to observational data. In particular, we select nonpolluted and very He-rich stars from the so-called chromosome map. Results. We re-determine the maximum helium mass fraction Y in NGC 6752, and find a value consistent with published results. We build toy models of clusters with various distributions of multiple populations and ensure that we are able to recover the input maximum Y. We then build synthetic clusters with the populations predicted by the FRMS scenario and find that while we slightly underestimate the maximum Y value, we are still able to detect stars much more He-rich than the current observed maximum Y. This result still holds even in synthetic clusters that contain less He-rich stars than predicted by the FRMS scenario. It is easier to determine the maximum Y on main sequence stars than on red giant branch stars, but qualitatively the results are unaffected by the sample choice. Conclusions. We show that in NGC 6752 it is unlikely that stars more He-rich than the current observational limit of about 0.3 (in mass fraction) are present.

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Sodium abundances of AGB and RGB stars in Galactic globular clusters

Cited by 31 publications

References 135 publications

Lithium in NGC 2243 and NGC 104

Lithium in NGC 2243 and NGC 104

When Does the Onset of Multiple Stellar Populations in Star Clusters Occur? III. No Evidence of Significant Chemical Variations in Main-sequence Stars of NGC 419

Maximum helium content of multiple populations in the globular cluster NGC 6752

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