VLT-FLAMES analysis of 8 giants in the bulge metal-poor globular cluster NGC 6522: oldest cluster in the Galaxy? Analysis of 8 giants in NGC 6522

被引:66
|
作者
Barbuy, B. [1 ]
Zoccali, M. [2 ]
Ortolani, S. [3 ]
Hill, V. [4 ]
Minniti, D. [2 ,5 ]
Bica, E. [6 ]
Renzini, A. [7 ]
Gomez, A. [8 ]
机构
[1] Univ Sao Paulo, IAG, BR-05508900 Sao Paulo, Brazil
[2] Pontificia Univ Catolica Chile, Dept Astron & Astrofis, Santiago 22, Chile
[3] Univ Padua, Dipartimento Astron, I-35122 Padua, Italy
[4] Univ Nice Sophia Antipolis, CNRS, CASSIOPEE, Observ Cote Azur, F-06304 Nice 4, France
[5] Vatican Observ, Vatican City, Vatican
[6] Univ Fed Rio Grande do Sul, Dept Astron, BR-91501970 Porto Alegre, RS, Brazil
[7] Osserv Astron Padova, I-35122 Padua, Italy
[8] Observ Paris, F-92195 Meudon, France
基金
美国国家航空航天局; 巴西圣保罗研究基金会; 美国国家科学基金会;
关键词
stars: abundances; galaxy: bulge; galaxy: globular clusters: individual: NGC 6522; RR LYRAE STARS; COLOR-MAGNITUDE DIAGRAMS; HORIZONTAL-BRANCH STARS; CA II TRIPLET; METALLICITY SCALE; GALACTIC BULGE; STELLAR PARAMETERS; RADIAL-VELOCITY; VARIABLE-STARS; VI PHOTOMETRY;
D O I
10.1051/0004-6361/200912748
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
Context. NGC 6522 has been the first metal-poor globular cluster identified in the bulge by Baade. Despite its importance, very few high-resolution abundance analyses of stars in this cluster are available. The bulge metal-poor clusters may be important tracers of the early chemical enrichment of the Galaxy. Aims. The main purpose of this study is to determine metallicity and elemental ratios in individual stars of NGC 6522. Methods. High-resolution spectra of 8 giants of the bulge's globular cluster NGC 6522 were obtained at the 8m VLT UT2-Kueyen telescope with the FLAMES+GIRAFFE spectrograph. Multiband V, I, J, K-s photometry was used to derive effective temperatures as reference values. Spectroscopic parameters were derived from Fe I and Fe II lines, and adopted for the derivation of abundance ratios. Results. The present analysis provides a metallicity [Fe/H] = -1.0 +/- 0.2. The alpha-elements oxygen, magnesium and silicon show [O/Fe] = +0.4 +/- 0.3, [Mg/Fe] = [Si/Fe] = +0.25 +/- 0.15, whereas calcium and titanium show shallower ratios of [Ca/Fe] = [Ti/Fe] = +0.15 +/- 0.15. The neutron-capture r-process element europium appears to be overabundant by [Eu/Fe] = +0.4 +/- 0.4. The neutron-capture s-elements lanthanum and barium are enhanced by [La/Fe] = +0.35 +/- 0.2 and [Ba/Fe] = +0.5 +/- 0.5. The large internal errors, indicating the large star-to-star variation in the barium and europium abundances, are also discussed. Conclusions. The moderate metallicity combined to a blue horizontal branch (BHB), are characteristics similar to those of HP 1 and NGC 6558, pointing to a population of very old globular clusters in the Galactic bulge. Also, the abundance ratios in NGC 6522 resemble those in HP 1 and NGC 6558. The ultimate conclusion is that the bulge is old, and went through an early prompt chemical enrichment.
引用
收藏
页码:405 / U533
页数:15
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