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(Reference retrieved automatically from Web of Science through information on FAPESP grant and its corresponding number as mentioned in the publication by the authors.)

High-resolution abundance analysis of four red giants in the globular cluster NGC 6558

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Author(s):
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Barbuy, B. [1] ; Muniz, L. [1] ; Ortolani, S. [2, 3] ; Ernandes, H. [1] ; Dias, B. [4, 5] ; Saviane, I. [4] ; Kerber, L. [6] ; Bica, E. [7] ; Perez-Villegas, A. [1] ; Rossi, L. [8] ; Held, E. V. [3]
Total Authors: 11
Affiliation:
[1] Univ Sao Paulo, IAG, Rua Matao 1226, BR-05508900 Sao Paulo - Brazil
[2] Univ Padua, Dipartimento Fis & Astron, I-35122 Padua - Italy
[3] INAF, Osservatorio Astron Padova, Vicolo Osservatorio 5, I-35122 Padua - Italy
[4] European Southern Observ, Alonso Cordova 3107, Santiago - Chile
[5] Univ Andres Bello, Fac Ciencias Exactas, Av Fernandez Concha 700, Santiago - Chile
[6] Univ Estadual Santa Cruz, DCET, Rodovia Jorge Amado, Km 16, BR-45662000 Ilheus, BA - Brazil
[7] Univ Fed Rio Grande do Sul, Dept Astron, CP 15051, BR-91501970 Porto Alegre, RS - Brazil
[8] Swinburne Univ Technol, Ctr Astrophys & Supercomp, Hawthorn, Vic 3122 - Australia
Total Affiliations: 8
Document type: Journal article
Source: Astronomy & Astrophysics; v. 619, NOV 21 2018.
Web of Science Citations: 4
Abstract

Context. NGC 6558 is a bulge globular cluster with a blue horizontal branch (BHB), combined with a metallicity of {[}Fe/H] approximate to -1.0. It is similar to HP 1 and NGC 6522, which could be among the oldest objects in the Galaxy. Element abundances in these clusters could reveal the nature of the first supernovae. Aims. We aim to carry out detailed spectroscopic analysis for four red giants of NGC 6558, in order to derive the abundances of the light elements C, N, O, Na, Al, the alpha-elements Mg, Si, Ca, Ti, and the heavy elements Y, Ba, and Eu. Methods. High-resolution spectra of four stars with FLAMES-UVES at VLT UT2-Kueyen were analysed. Spectroscopic parameter-derivation was based on excitation and ionization equilibrium of Fe I and Fe II. Results. This analysis results in a metallicity of {[}Fe/H] = -1.17 +/- 0.10 for NGC 6558. We find the expected alpha-element enhancements in O and Mg with {[}O/Fe] = +0.40, {[}Mg/Fe] = +0.33, and low enhancements in Si and Ca. Ti has a moderate enhancement of {[}Ti/Fe] = +0.22. The r-element Eu appears very enhanced with a mean value of {[}Eu/Fe] = +0.63. The first peak s-elements Y and Sr are also enhanced, these results have however to be treated with caution, given the uncertainties in the continuum definition; the use of neutral species (Sr I, Y I), instead of the dominant ionized species is another source of uncertainty. Ba appears to have a solar abundance ratio relative to Fe. Conclusions. NGC 6558 shows an abundance pattern that could be typical of the oldest inner bulge globular clusters, together with the pattern in the similar clusters NGC 6522 and HP 1. They show low abundances of the odd-Z elements Na and Al, and of the explosive nucleosynthesis alpha-elements Si, Ca, and Ti. The hydrostatic burning alpha-elements O and Mg are normally enhanced as expected in old stars enriched with yields from core-collapse supernovae, and the iron-peak elements Mn, Cu, Zn show low abundances, which is expected for Mn and Cu, but not for Zn. Finally, the cluster trio NGC 6558, NGC 6522, and HP 1 have relatively high abundances of first-peak heavy elements, variable second-peak element Ba, and the r-element Eu is enhanced. The latter is particularly high in NGC 6558. (AU)

FAPESP's process: 17/15893-1 - Globular cluster orbits of bulge: the formation and evolution of the Milky Way
Grantee:Maria de Los Angeles Perez Villegas
Support type: Scholarships in Brazil - Post-Doctorate
FAPESP's process: 16/24814-5 - Star clusters as tracers of formation and evolution of the Galactic bulge and Magellanic Clouds: modeling of data from the Hubble Space Telescope, SOAR, Gemini and Very Large Telescope.
Grantee:Beatriz Leonor Silveira Barbuy
Support type: Research Grants - Visiting Researcher Grant - Brazil