Chemical abundances in LMC stellar populations^*,**,***

I. The inner disk sample

¹ IP&D, Universidade do Vale do Paraíba, Av. Shishima Hifumi, 2911, São, José dos Campos, 12244-000 SP, Brazil
²  Instituto Astronômico e Geofísico (USP), Rua do Matão 1226, Cidade Universitária, 05508-900 São Paulo, Brazil e-mail: pompeia@univap.br
³ Observatoire de Paris-Meudon, GEPI and CNRS UMR 8111, 92195 Meudon Cedex, France e-mail: [Vanessa.Hill;Monique.Spite]@obspm.fr
⁴ School of Mathematics and Physics, University of Tasmania, Private Bag 37, Hobart, TAS 7001, Australia
⁵ Kapteyn Astronomical Institute, University of Groningen, Postbus 800, 9700 AV Groningen, The Netherlands e-mail: cole@astro.rug.nl
⁶ European Southern Observatory, Karl Schwarschild Str. 2, 85748 Garching b. München, Germany e-mail: [fprimas;mromanie;lpasquin]@eso.org
⁷ Edinburg SUPA, School of Physics, University of Edinburgh, IfA, Blackford Hill, Edinburgh EH9 3HJ, UK e-mail: mrc@roe.ac.uk
⁸ Department of Physics and Astronomy, 4129 Frederick Reines Hall, University of California, Irvine, CA 92697-4575, USA e-mail: smecker@carina.ps.uci.edu

Received: 13 January 2006
Accepted: 13 November 2007

Abstract

Aims.We have used FLAMES (the Fibre Large Array Multi Element Spectrograph) at the VLT-UT2 telescope to obtain spectra of a large sample of red giant stars from the inner disk of the LMC, ~2 kpc from the center of the galaxy. We investigate the chemical abundances of key elements to understand the star formation and evolution of the LMC disk: heavy and light [ s-process/Fe] and [ α/Fe] give constraints on the time scales of formation of the stellar population. Cu, Na, Sc, and the iron-peak elements are also studied aiming to better understand the build up of the elements of this population and the origin of these elements. We aim to provide a more complete picture of the LMC's evolution by compiling a large sample of field star abundances.

Methods.LTE abundances were derived using line spectrum synthesis or equivalent width analysis. We used OSMARCS model atmospheres and an updated line list.

Results.We find that the alpha-elements Ca, Si, and Ti show lower [X/Fe] ratios than Galactic stars at the same [Fe/H], with most [Ca/Fe] being subsolar. The [O/Fe] and [Mg/Fe] ratios are slightly deficient, with Mg showing some overlap with the Galactic distribution, while Sc and Na follow the underabundant behavior of Ca, with subsolar distributions. For the light s-process elements Y and Zr, we find underabundant values compared to their Galactic counterparts. The [La/Fe] ratios are slightly overabundant relative to the galactic pattern showing low scatter, while the [Ba/Fe] are enhanced, with a slight increasing trend for metallicities [ Fe/H dex. The [ heavy-s/light-s] ratios are high, showing a slow, increasing trend with metallicity. We were surprised to find an offset for three of the iron-peak elements. We found an offset for the [iron-peak/Fe] ratios of Ni, Cr, and Co, with an underabundant pattern and subsolar values, while Vanadium ratios track the solar value. Copper shows very low abundances in our sample for all metallicities, compatible with those of the Galaxy only for the most metal-poor stars. The overall chemical distributions of this LMC sample indicates a slower star formation history relative to that of the solar neighborhood, with a higher contribution from type Ia supernovae relative to type II supernovae.