Abundances of Mg and K in the atmospheres of turn-off starsin Galactic globular cluster 47 Tucanae

Černiauskas, A.; Kučinskas, A.; Klevas, J.; Dobrovolskas, V.; Коротин, С. А.; Bonifacio, P.; Ludwig, H.‐G.; Caffau, E.; Steffen, M.

doi:10.1051/0004-6361/201731659

A&A

2018

DOI: 10.1051/0004-6361/201731659

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Abundances of Mg and K in the atmospheres of turn-off starsin Galactic globular cluster 47 Tucanae

A. Černiauskas¹,

A. Kučinskas²,

J. Klevas³

et al.

Abstract: Aims. We determined abundances of Mg and K in the atmospheres of 53 (Mg) and 75 (K) turn-off (TO) stars of the Galactic globular cluster 47 Tuc. The obtained abundances, together with those of Li, O, and Na that we had earlier determined for the same sample of stars, were used to search for possible relations between the abundances of K and other light elements, Li, O, Na, and Mg, as well as the connections between the chemical composition of TO stars and their kinematical properties. Methods. Abundances of Mg… Show more

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Cited by 3 publications

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Abundance of zinc in the red giants of Galactic globular cluster 47 Tucanae

Černiauskas

Kučinskas

Klevas

et al. 2018

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Aims. We investigate possible relations between the abundances of zinc and the light elements sodium, magnesium, and potassium in the atmospheres ofred giant branch (RGB) stars of the Galactic globular cluster 47 Tuc and study connections between the chemical composition and dynamical properties of the cluster RGB stars. Methods. The abundance of zinc was determined in 27 RGB stars of 47 Tuc using 1D local thermal equilibrium (LTE) synthetic line profile fitting to the high-resolution 2dF/HERMES spectra obtained with the Anglo-Australian Telescope (AAT). Synthetic spectra used in the fitting procedure were computed with the SYNTHE code and 1D ATLAS9 stellar model atmospheres.Results. The average 1D LTE zinc-to-iron abundance ratio and its RMS variations due to star-to-star abundance spread determined in the sample of 27 RGB stars is [Zn/Fe] 1D LTE = 0.11 ± 0.09. We did not detect any statistically significant relations between the abundances of zinc and those of light elements. Neither did we find any significant correlation or anticorrelation between the zinc abundance in individual stars and their projected distance from the cluster center. Finally, no statistically significant relation between the absolute radial velocities of individual stars and the abundance of zinc in their atmospheres was detected. The determined average [Zn/Fe] 1DLTE ratio agrees well with those determined in this cluster in earlier studies and nearly coincides with that of Galactic field stars at this metallicity. All these results suggest that nucleosynthesis of zinc and light elements proceeded in separate, unrelated pathways in 47 Tuc.

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Abundance of zinc in the red giants of Galactic globular cluster 47 Tucanae

Černiauskas

Kučinskas

Klevas

et al. 2018

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Probing 3D and NLTE models using APOGEE observations of globular cluster stars

Masseron

Osorio

García-Hernández

et al. 2021

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Context. Hydrodynamical (or 3D) and non-local thermodynamic equilibrium (NLTE) effects are known to affect abundance analyses. However, there are very few observational abundance tests of 3D and NLTE models. Aims. We developed a new way of testing the abundance predictions of 3D and NLTE models, taking advantage of large spectroscopic survey data. Methods. We use a line-by-line analysis of the Apache Point Observatory Galactic Evolution Experiment (APOGEE) spectra (H band) with the Brussels Automatic Code for Characterizing High accUracy Spectra (BACCHUS). We compute line-by-line abundances of Mg, Si, Ca, and Fe for a large number of globular cluster K giants in the APOGEE survey. We compare this line-by-line analysis against NLTE and 3D predictions. Results. While the 1D–NLTE models provide corrections in the right direction, there are quantitative discrepancies between different models. We observe a better agreement with the data for the models including reliable collisional cross-sections. The agreement between data and models is not always satisfactory when the 3D spectra are computed in LTE. However, we note that for a fair comparison, 3D corrections should be computed with self-consistently derived stellar parameters, and not on 1D models with identical stellar parameters. Finally, we focus on 3D and NLTE effects on Fe lines in the H band, where we observe a systematic difference in abundance relative to the value from the optical. Our results suggest that the metallicities obtained from the H band are more accurate in metal-poor giants. Conclusions. Current 1D–NLTE models provide reliable abundance corrections, but only when the atom data and collisional cross-sections are accurate and complete. Therefore, we call for more atomic data for NLTE calculations. In contrast, we show that 3D corrections in LTE conditions are often not accurate enough, thus confirming that 3D abundance corrections are only valid when NLTE is taken into account. Consequently, more extended self-consistent 3D–NLTE computations need to be made. The method we have developed for testing 3D and NLTE models could be extended to other lines and elements, and is particularly suited for large spectroscopic surveys.

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Curiouser and curiouser: the peculiar chemical composition of the Li- and Na-rich star in ω Centauri

Mucciarelli

Monaco

Bonifacio

et al. 2021

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We present a multi-instrument spectroscopic analysis of the unique Li- and Na-rich giant star #25664 in ω Centauri, using spectra acquired with FLAMES-GIRAFFE, X-shooter, UVES, and HARPS. Li and Na abundances have been derived from the UVES spectrum using transitions weakly sensitive to non-local thermodynamic equilibrium and assumed isotopic ratios. This new analysis confirms the surprising Li and Na abundances of this star (A(Li)NLTE = +2.71 ± 0.07 dex, [Na/Fe]NLTE = +1.00 ± 0.05 dex). Additionally, we provide new pieces of evidence for its chemical characterisation. The 12C∕13C isotopic ratio (15 ± 2) shows that this star has not yet undergone the extra-mixing episode usually associated with the red giant branch bump. Therefore, we can rule out the scenario of efficient deep extra mixing during the red giant branch phase envisaged to explain the high Li and Na abundances. Also, the star exhibits high abundances of both C and N ([C/Fe] = +0.45 ± 0.16 dex and [N/Fe] = +0.99 ± 0.20 dex), which is not compatible with the typical C-N anti-correlation observed in globular cluster stars. We found evidence of a radial velocity variability in #25664, suggesting that the star could be part of a binary system, likely having accreted material from a more massive companion when the latter was evolving in the asymptotic giant branch (AGB) phase. Viable candidates for the donor star are AGB stars with 3–4 M⊙ and super-AGB stars (~7–8 M⊙), both of which are able to produce Li- and Na-rich material. Alternatively, the star could have formed from the pure ejecta of a super-AGB star before the dilution with primordial gas occurred.

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Abundances of Mg and K in the atmospheres of turn-off starsin Galactic globular cluster 47 Tucanae

Cited by 3 publications

References 46 publications

Abundance of zinc in the red giants of Galactic globular cluster 47 Tucanae

Abundance of zinc in the red giants of Galactic globular cluster 47 Tucanae

Probing 3D and NLTE models using APOGEE observations of globular cluster stars

Curiouser and curiouser: the peculiar chemical composition of the Li- and Na-rich star in ω Centauri

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