The metal content of the bulge globular cluster NGC 6528

Free access article

Issue		A&A Volume 423, Number 2, August IV 2004


Page(s)		507 - 516
Section		Galactic structure, stellar clusters and populations
DOI		http://dx.doi.org/10.1051/0004-6361:20041014

A&A 423, 507-516 (2004)
DOI: 10.1051/0004-6361:20041014

The metal content of the bulge globular cluster NGC 6528

M. Zoccali^{1, 2}, B. Barbuy³, V. Hill⁴, S. Ortolani⁵, A. Renzini⁶, E. Bica⁷, Y. Momany⁵, L. Pasquini⁶, D. Minniti¹ and R. M. Rich⁸

¹ Universidad Catolica de Chile, Department of Astronomy & Astrophysics, Casilla 306, Santiago 22, Chile
    e-mail: [mzoccali;dante]@astro.puc.cl
² Princeton University Observatory, Peyton Hall, Princeton, NJ 08544, USA
³ Universidade de São Paulo, IAG, Rua do Matão 1226, Cidade Universitária, São Paulo 05508-900, Brazil
    e-mail: barbuy@astro.iag.usp.br
⁴ Observatoire de Paris-Meudon, 92195 Meudon Cedex, France
    e-mail: Vanessa.Hill@obspm.fr
⁵ Università di Padova, Dipartimento di Astronomia, Vicolo dell'Osservatorio 2, 35122 Padova, Italy
    e-mail: [ortolani;momany]@pd.astro.it
⁶ European Southern Observatory, Karl Schwarzschild Strasse 2, 85748 Garching bei München, Germany
    e-mail: [arenzini;lpasquin]@eso.org
⁷ Universidade Federal do Rio Grande do Sul, Departamento de Astronomia, CP 15051, Porto Alegre 91501-970, Brazil
    e-mail: bica@if.ufrgs.br
⁸ UCLA, Department of Physics & Astronomy, 8979 Math-Sciences Building, Los Angeles, CA 90095-1562, USA
    e-mail: rmr@astro.ucla.edu

(Received 2 April 2004 / Accepted 10 May 2004)

Abstract
High resolution spectra of five stars in the bulge globular cluster NGC 6528 were obtained at the 8m VLT UT2-Kueyen telescope with the UVES spectrograph. Out of the five stars, two of them showed evidence of binarity. The target stars belong to the horizontal and red giant branch stages, at $4000 < T_{\rm eff}< 4800$ K. Multiband V, I, J, H, $K_{\rm s}$ photometry was used to derive initial effective temperatures and gravities. The main purpose of this study is the determination of metallicity and elemental ratios for this template bulge cluster, as a basis for the fundamental calibration of metal-rich populations. The present analysis provides a metallicity $\rm [Fe/H] = -0.1\pm0.2$ and the $\alpha$ -elements O, Mg and Si, show [ $\alpha$ /Fe] $\approx$ +0.1, whereas Ca and Ti are around the solar value or below, resulting in an overall metallicity Z $\approx$ $Z_{\odot}$ .

Key words: Galaxy: bulge -- globular clusters: individual: NGC 6528 -- stars: abundances -- stars: atmospheres

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