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

Mucciarelli, A, Monaco, L, Bonifacio, P, Salaris, M, Saviane, I, Lanzoni, B, Momany, Y and Lo Curto, G (2021) Curiouser and curiouser: The peculiar chemical composition of the Li: The Na-rich star in ω Centauri. Astronomy and Astrophysics, 652. ISSN 0004-6361

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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 12C13C 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.

Item Type: Article
Additional Information: Curiouser and curiouser: the peculiar chemical composition of the Li- and Na-rich star in ω Centauri A. Mucciarelli, L. Monaco, P. Bonifacio, M. Salaris, I. Saviane, B. Lanzoni, Y. Momany and G. Lo Curto A&A, 652 (2021) A139 Published online: 24 August 2021 DOI: 10.1051/0004-6361/202140796
Uncontrolled Keywords: 0201 Astronomical and Space Sciences
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Divisions: Astrophysics Research Institute
Publisher: EDP Sciences
Date Deposited: 20 Sep 2021 11:16
Last Modified: 20 Sep 2021 11:30
DOI or ID number: 10.1051/0004-6361/202140796
URI: https://researchonline.ljmu.ac.uk/id/eprint/15519
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