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(Referência obtida automaticamente do Web of Science, por meio da informação sobre o financiamento pela FAPESP e o número do processo correspondente, incluída na publicação pelos autores.)

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

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Autor(es):
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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]
Número total de Autores: 11
Afiliação do(s) autor(es):
[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
Número total de Afiliações: 8
Tipo de documento: Artigo Científico
Fonte: Astronomy & Astrophysics; v. 619, NOV 21 2018.
Citações Web of Science: 4
Resumo

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)

Processo FAPESP: 17/15893-1 - Órbitas de aglomerados globulares do bojo: formação e evolução da Via Láctea
Beneficiário:Maria de Los Angeles Perez Villegas
Linha de fomento: Bolsas no Brasil - Pós-Doutorado
Processo FAPESP: 16/24814-5 - Aglomerados estelares como tracadores da formacão e evolucão do bojo Galáctico e Nuvens de Magalhães: modelamento de dados do Telescópio Espacial Hubble, SOAR, Gemini e Very Large Telescope
Beneficiário:Beatriz Leonor Silveira Barbuy
Linha de fomento: Auxílio à Pesquisa - Pesquisador Visitante - Brasil