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Letter to the Editor

Chemical similarities between Galactic bulge and local thick disk red giant stars

¹ Centro de Astrofísica da Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal
² Research School of Astronomy and Astrophysics, The Australian National University, Cotter Road, Weston, ACT 2611, Australia
³ Max Planck Institute for Astrophysics, Postfach 1317, 85741 Garching, Germany e-mail: asplund@mpa-garching.mpg.de
⁴ Universidade de São Paulo, IAG, Rua do Matão 1226, Cidade Universitária, São Paulo 05508-900, Brazil
⁵ National Optical Astronomy Observatory, Casilla 603, La Serena, Chile
⁶ On leave from Observatório Nacional, Rio de Janeiro, Brazil
⁷ Geneva Observatory, Ch. des Maillettes 51, 1290 Sauverny, Switzerland
⁸ OAT/INAF, Via Tiepolo 11, Trieste 34131, Italy
⁹ McDonald Observatory and Department of Astronomy, University of Texas, RLM 15.306, Austin, TX 78712-1083, USA

Received: 15 January 2008
Accepted: 17 April 2008

Abstract

Context.The evolution of the Milky Way bulge and its relationshipwith the other Galactic populations is still poorly understood.The bulge has been suggested to be either a merger-driven classical bulge orthe product of a dynamical instability of the inner disk.

Aims.To probe the star formation history, the initial massfunction and stellar nucleosynthesis of the bulge, we performedan elemental abundance analysis of bulge red giant stars. We also completed an identical study of local thin disk, thick disk and halo giants to establish the chemical differences and similarities between the various populations.

Methods.High-resolution infrared spectra of 19 bulge giants and 49 comparisongiants in the solar neighborhood were acquired with Gemini/Phoenix.All stars have similar stellar parameters but cover a broad range in metallicity. A standard 1D local thermodynamic equilibrium analysis yielded the abundances of C, N, O and Fe.A homogeneous and differential analysis of the bulge, halo, thin disk and thick disk stars ensured that systematic errors were minimized.

Results.We confirm the well-established differences for [O/Fe] (at a givenmetallicity) between the local thin and thick disks. For the elements investigated, we find no chemical distinction betweenthe bulge and the local thick disk, which is in contrastto previous studies relying on literature values for disk dwarf stars in the solar neighborhood.

Conclusions.Our findings suggest that the bulge and local thick disk experienced similar, but not necessarily shared, chemical evolution histories. We argue that their formation timescales, star formation rates andinitial mass functions were similar.