Zinc abundances in Galactic bulge field red giants: Implications for damped Lyman-α systems^⋆,⋆⋆

¹ Universidade de São Paulo, IAG, Rua do Matão 1226, Cidade Universitária, 05508-900 São Paulo, Brazil
e-mail: barbuy@astro.iag.usp.br
² Université de Sophia-Antipolis, Observatoire de la Côte d’Azur, CNRS UMR 6202, BP4229, 06304 Nice Cedex 4, France
³ Universidad Catolica de Chile, Instituto de Astrofisica, Casilla 306, 22 Santiago, Chile
⁴ Millenium Institute of Astrophysics, Av. Vicuña Mackenna 4860, Macul, Santiago, Chile
⁵ Departamento de Ciencias Fisicas, Universidad Andres Bello, Republica 220, Santiago, Chile
⁶ Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
⁷ Università di Padova, Dipartimento di Astronomia, Vicolo dell’Osservatorio 2, 35122 Padova, Italy
⁸ Observatoire de Paris-Meudon, 92195 Meudon Cedex, France

Received: 20 January 2015
Accepted: 13 May 2015

Abstract

Context. Zinc in stars is an important reference element because it is a proxy to Fe in studies of damped Lyman-α systems (DLAs), permitting a comparison of chemical evolution histories of bulge stellar populations and DLAs. In terms of nucleosynthesis, it behaves as an alpha element because it is enhanced in metal-poor stars. Abundance studies in different stellar populations can give hints to the Zn production in different sites.

Aims. The aim of this work is to derive the iron-peak element Zn abundances in 56 bulge giants from high resolution spectra. These results are compared with data from other bulge samples, as well as from disk and halo stars, and damped Lyman-α systems, in order to better understand the chemical evolution in these environments.

Methods. High-resolution spectra were obtained using FLAMES+UVES on the Very Large Telescope. We computed the Zn abundances using the Zn i lines at 4810.53 and 6362.34 Å. We considered the strong depression in the continuum of the Zn i 6362.34 Å line, which is caused by the wings of the Ca i 6361.79 Å line suffering from autoionization. CN lines blending the Zn i 6362.34 Å line are also included in the calculations.

Results. We find [Zn/Fe] = +0.24 ± 0.02 in the range −1.3 < [Fe/H] < −0.5 and [Zn/Fe] = + 0.06 ± 0.02 in the range −0.5 < [Fe/H] < −0.1, whereas for [Fe/H] ≥ −0.1, it shows a spread of −0.60 < [Zn/Fe] < + 0.15, with most of these stars having low [Zn/Fe] < 0.0. These low zinc abundances at the high metallicity end of the bulge define a decreasing trend in [Zn/Fe] with increasing metallicities. A comparison with Zn abundances in DLA systems is presented, where a dust-depletion correction was applied for both Zn and Fe. When we take these corrections into account, the [Zn/Fe] vs. [Fe/H] of the DLAs fall in the same region as the thick disk and bulge stars. Finally, we present a chemical evolution model of Zn enrichment in massive spheroids, representing a typical classical bulge evolution.