The Gaia-ESO Survey: Calibration strategy^⋆,⋆⋆

¹ INAF–Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
e-mail: pancino@arcetri.inaf.it
² ASI Science Data Center, via del Politecnico s/n, 00133 Roma, Italy
³ Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool L3 5RF, UK
⁴ INAF–Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
⁵ INAF–Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monte Porzio Catone, Roma, Italy
⁶ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, US
⁷ Instituto de Astrofísica, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, 782-0436 Macul, Santiago, Chile
⁸ Millennium Institute of Astrophysics, Av. Vicuña Mackenna 4860, 782-0436 Macul, Santiago, Chile
⁹ Dipartimento di Fisica e Astronomia, Alma Mater Studiorum, Università di Bologna, Viale Berti Pichat 6/2, 40127 Bologna, Italy
¹⁰ Department of Physics and Astronomy, Uppsala University, Box 516, 751 20 Uppsala, Sweden
¹¹ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
¹² Royal Observatory of Belgium, Ringlaan 3, 1180 Brussels, Belgium
¹³ Institut d’Astrophysique et de Géophysique, Université de Liège, Allée du 6 Août, Bât. B5c, 4000 Liège, Belgium
¹⁴ Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain
¹⁵ Departamento de Astrofísica, Universidad de La Laguna, 38205 La Laguna, Tenerife, Spain
¹⁶ Laboratoire d’astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, allée Geoffroy Saint-Hilaire, 33615 Pessac, France
¹⁷ Dipartimento di Fisica e Astronomia, Università di Padova, Vicolo dell’Osservatorio 2, 35122 Padova, Italy
¹⁸ Leibnitz Institute für Astrophysics (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
¹⁹ Observatoire de Genève, Université de Genève, 1290 Versoix, Switzerland
²⁰ Núcleo de Astronomía, Facultad de Ingeniería, Universidad Diego Portales, Av. Ejercito 441, Santiago, Chile
²¹ GEPI, Observatoire de Paris, PSL Research University, CNRS, Univ. Paris Diderot, Sorbonne Paris Cité, 5 place Jules Janssen, 92190 Meudon, France
²² Lund Observatory, Department of Astronomy and Theoretical Physics, Box 43, 221 00 Lund, Sweden
²³ Research School of Astronomy & Astrophysics, Australian National University, Cotter Road, Weston Creek, ACT 2611, Australia
²⁴ Centre for Astrophysics Research, STRI, University of Hertfordshire, College Lane Campus, Hatfield AL10 9AB, UK
²⁵ Astrophysics Group, Research Institute for the Environment, Physical Sciences and Applied Mathematics, Keele University, Keele, Staffordshire ST5 5BG, UK
²⁶ INAF–Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy
²⁷ INAF–Padova Observatory, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
²⁸ Instituto de Astrofísica de Andalucía-CSIC, Apdo. 3004, 18080 Granada, Spain
²⁹ Institute of Astronomy, University of Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, UK
³⁰ Dipartimento di Fisica e Astronomia, Sezione Astrofisica, Università di Catania, via S. Sofia 78, 95123 Catania, Italy
³¹ Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, ul. Bartycka 18, 00-716 Warsaw, Poland
³² Institut d’Astronomie et d’Astrophysique, Université libre de Brussels, Boulevard du Triomphe, 1050 Brussels, Belgium
³³ Instituto de Física y Astronomía, Universidad de Valparaíso, Chile
³⁴ INAF–Osservatorio Astrofisico di Catania, via S. Sofia 78, 95123 Catania, Italy
³⁵ Departamento de Ciencias Fisicas, Universidad Andres Bello, Republica 220, Santiago, Chile
³⁶ European Southern Observatory, Alonso de Cordova 3107 Vitacura, Santiago de Chile, Chile
³⁷ Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, rua das Estrelas, 4150-762 Porto, Portugal
³⁸ Physics Department, Lancaster University, Lancaster LA1 4YB, UK
³⁹ UPJV, Université de Picardie Jules Verne, 33 rue St Leu, 80080 Amiens, France

Received: 1 August 2016
Accepted: 20 October 2016

Abstract

The Gaia-ESO survey (GES) is now in its fifth and last year of observations and has produced tens of thousands of high-quality spectra of stars in all Milky Way components. This paper presents the strategy behind the selection of astrophysical calibration targets, ensuring that all GES results on radial velocities, atmospheric parameters, and chemical abundance ratios will be both internally consistent and easily comparable with other literature results, especially from other large spectroscopic surveys and from Gaia. The calibration of GES is particularly delicate because of (i) the large space of parameters covered by its targets, ranging from dwarfs to giants, from O to M stars; these targets have a large wide of metallicities and also include fast rotators, emission line objects, and stars affected by veiling; (ii) the variety of observing setups, with different wavelength ranges and resolution; and (iii) the choice of analyzing the data with many different state-of-the-art methods, each stronger in a different region of the parameter space, which ensures a better understanding of systematic uncertainties. An overview of the GES calibration and homogenization strategy is also given, along with some examples of the usage and results of calibrators in GES iDR4, which is the fourth internal GES data release and will form the basis of the next GES public data release. The agreement between GES iDR4 recommended values and reference values for the calibrating objects are very satisfactory. The average offsets and spreads are generally compatible with the GES measurement errors, which in iDR4 data already meet the requirements set by the main GES scientific goals.