Chemical abundances of 451 stars from the HARPS GTO planet search program ^*,**

Thin disc, thick disc, and planets

¹ Centro de Astrofísica, Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal e-mail: nuno.santos@astro.up.pt
² Departamento de Física, Universidade de Aveiro, Campus de Santiago 3810-193 Aveiro, Portugal
³ Observatoire de Genève, 51 ch. des Maillettes, 1290 Sauverny, Switzerland
⁴ Departamento de Matemática Aplicada, Faculdade de Ciências da Universidade do Porto, Portugal
⁵ Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain

Received: 11 November 2008
Accepted: 14 January 2009

Abstract

We present a uniform study of the chemical abundances of 12 elements (Si, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Na, Mg, and Al) derived from the spectra of 451 stars observed as part of one of the HARPS GTO planet search programs. Sixty eight of these are planet-bearing stars. The main goals of our work are: i) the investigation of possible differences between the abundances of stars with and without planets; ii) the study of the possible differences in the abundances of stars in the thin and the thick disc. We confirm that there is a systematically higher metallicity in planet host stars, when compared to non planet-hosts, common to all studied species. We also found that there is no difference in the galactic chemical evolution trends of the stars with and without planets. Stars that harbour planetary companions simply appear to be in the high metallicity tail of the distribution. We also confirm that Neptunian and super-Earth class planets may be easier to find at lower metallicities. A statistically significative abundance difference between stars of the thin and the thick disc was found for [ Fe/H. However, the populations from the thick and the thin disc cannot be clearly separated.