UVES analysis of red giants in the bulge globular cluster NGC 6522

Barbuy, B.; Cantelli, E.; Muniz, L.; Souza, S. O.; Chiappini, C.; Hirschi, R.; Cescutti, G.; Pignatari, M.; Ortolani, S.; Kerber, L.; F. S. Maia, F.; Bica, E.; Depagne, E.

Abstract

Context: NGC 6522 is a moderately metal-poor bulge globular cluster ([Fe/H] -1.0), and it is a well-studied representative among a number of moderately metal-poor blue horizontal branch clusters located in the bulge. The NGC 6522 abundance pattern can give hints on the earliest chemical enrichment in the central Galaxy.
Aims: The aim of this study is to derive abundances of the light elements C and N; alpha elements O, Mg, Si, Ca, and Ti; odd-Z elements Na and Al; neutron-capture elements Y, Zr, Ba, La, and Nd; and the r-process element Eu. We verify if there are first-and second-generation stars: we find clear evidence of Na-Al, Na-N, and Mg-Al correlations, while we cannot identify the Na-O anti-correlation from our data.
Methods: High-resolution spectra of six red giants in the bulge globular cluster NGC 6522 were obtained at the 8m VLT UT2-Kueyen telescope with both the UVES and GIRAFFE spectrographs in FLAMES+UVES configuration. In light of Gaia data, it turned out that two of them are non-members, but these were also analysed. Spectroscopic parameters were derived through the excitation and ionisation equilibrium of Fe I and Fe II lines from UVES spectra. The abundances were obtained with spectrum synthesis. Comparisons of abundances derived from UVES and GIRAFFE spectra were carried out.
Results: The present analysis combined with previous UVES results gives a mean radial velocity of vrhel = -15.62±7.7 km s-1 and a metallicity of [Fe/H] = -1.05 ± 0.20 for NGC 6522. Mean abundances of alpha elements for the present four member stars are enhanced with [O/Fe] = +0.38, [Mg/Fe] = ≈+0.28, [Si/Fe] ≈ +0.19, and [Ca/Fe] ≈ +0.13, together with the iron-peak element [Ti/Fe] ≈ +0.13, and the r-process element [Eu/Fe] = +0.40. The neutron-capture elements Y, Zr, Ba, and La show enhancements in the +0.08 < [Y/Fe] < +0.90, 0.11 < [Zr/Fe] < +0.50, 0.00 < [Ba/Fe] < +0.63, 0.00 < [La/Fe] < +0.45, and -0.10 < [Nd/Fe] < +0.70 ranges. We also discuss the spread in heavy-element abundances.

Citation

Barbuy, B., Cantelli, E., Muniz, L., Souza, S. O., Chiappini, C., Hirschi, R., Cescutti, G., Pignatari, M., Ortolani, S., Kerber, L., F. S. Maia, F., Bica, E., & Depagne, E. (2021). UVES analysis of red giants in the bulge globular cluster NGC 6522. Astronomy and Astrophysics, 654, Article A29. https://doi.org/10.1051/0004-6361/202140815

• Journal Article Type: Article
• Acceptance Date: Jul 3, 2021
• Publication Date: Oct 5, 2021
• Deposit Date: Nov 19, 2021
• Publicly Available Date: Feb 3, 2022
• Journal: Astronomy and Astrophysics
• Print ISSN: 0004-6361
• Electronic ISSN: 1432-0746
• Publisher: EDP Sciences
• Peer Reviewed: Peer Reviewed
• Volume: 654
• Article Number: A29
• DOI: https://doi.org/10.1051/0004-6361/202140815
• Keywords: stars: abundances; globular clusters: individual: NGC 6522; Galaxy: bulge
• Public URL: https://hull-repository.worktribe.com/output/3840539