Gaia FGK benchmark stars: Metallicity^⋆,⋆⋆

¹ Institute of Astronomy, University of Cambridge, Madingley Rd, Cambridge CB3 0HA, UK
e-mail: pjofre@ast.cam.ac.uk
² LAB UMR 5804, Univ. Bordeaux – CNRS, 33270 Floirac, France
³ Department of Physics and Astronomy, Uppsala University, Box 516, 75120 Uppsala, Sweden
e-mail: ulrike.heiter@physics.uu.se
⁴ Laboratoire Lagrange (UMR7293), Univ. Nice Sophia Antipolis, CNRS, Observatoire de la Côte d’Azur, 06304 Nice, France
⁵ INAF – Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
⁶ ASI Science Data Center, via del Politecnico s/n, 00133 Roma, Italy
⁷ INAF, Osservatorio Astronomico di Padova, Vicolo Osservatorio 5, Padova, 35122 Italy
⁸ Dipartimento di Fisica e Astronomia, Università di Padova, vicolo Osservatorio 3, 35122 Padova, Italy
⁹ INAF/Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, 50125 Firenze, Italy
¹⁰ Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85741 Garching, Germany
¹¹ Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain
¹² Institut d’Astronomie et d’Astrophysique, Univ. Libre de Bruxelles, CP 226, Bd du Triomphe, 1050 Bruxelles, Belgium
¹³ Dpto. Astrofísica, Facultad de CC. Físicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
¹⁴ Dipartimento di Fisica & Astronomia, Universitá degli Studi di Bologna, Viale Berti Pichat 6/2, 40127 Bologna, Italy
¹⁵ Department of Astronomy & Astrophysics, University of Chicago, Chicago IL 60637, USA
¹⁶ Centro de Astrofísica, Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal

Received: 2 August 2013
Accepted: 24 January 2014

Abstract

Context. To calibrate automatic pipelines that determine atmospheric parameters of stars, one needs a sample of stars, or “benchmark stars”, with well-defined parameters to be used as a reference.

Aims. We provide detailed documentation of the iron abundance determination of the 34 FGK-type benchmark stars that are selected to be the pillars for calibration of the one billion Gaia stars. They cover a wide range of temperatures, surface gravities, and metallicities.

Methods. Up to seven different methods were used to analyze an observed spectral library of high resolutions and high signal-to-noise ratios. The metallicity was determined by assuming a value of effective temperature and surface gravity obtained from fundamental relations; that is, these parameters were known a priori and independently from the spectra.

Results. We present a set of metallicity values obtained in a homogeneous way for our sample of benchmark stars. In addition to this value, we provide detailed documentation of the associated uncertainties. Finally, we report a value of the metallicity of the cool giant ψ Phe for the first time.