The Gaia-ESO Survey: processing FLAMES-UVES spectra^⋆

¹ INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
e-mail: gsacco@arcetri.inaf.it
² European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
³ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
⁴ Research School of Astronomy & Astrophysics, Australian National University, Cotter Road, Weston Creek, ACT 2611 Canberra, Australia
⁵ Rudolf Peierls Centre for Theoretical Physics, Keble Road, Oxford, OX1 3NP, UK
⁶ GEPI, Observatoire de Paris, CNRS, Université Paris Diderot, 5 place Jules Janssen, 92195 Meudon, France
⁷ Centre for Astronomy Research, University of Hertfordshire, Hatfield AL10 9AB, UK
⁸ Lund Observatory, Department of Astronomy and Theoretical Physics, Box 43, 221 00 Lund, Sweden
⁹ Institute of Astronomy, University of Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, UK
¹⁰ Astrophysics Group, Research Institute for the Environment, Physical Sciences and Applied Mathematics, Keele University, Keele ST5 5BG, UK
¹¹ INAF – Osservatorio Astronomico di Palermo, piazza del Parlamento 1, 90134 Palermo, Italy
¹² Departamento de Física, Ingeniería de Sistemas y Teoría de la Señal, Universidad de Alicante, Apdo. 99, 03080 Alicante, Spain
¹³ ESA, ESTEC, Keplerlaan 1, Po Box 299, 2200 AG Noordwijk, The Netherlands
¹⁴ Max-Planck Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
¹⁵ INAF – Padova Observatory, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
¹⁶ Instituto de Astrofísica de Andalucía-CSIC, Apdo. 3004, 18080 Granada, Spain
¹⁷ Instituto Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain
¹⁸ Universidad de La Laguna, Depart. de Astrofísica, 38206 La Laguna, Tenerife, Spain
¹⁹ Lund Observatory, Department of Astronomy and Theoretical Physics, Box 43, 221 00 Lund, Sweden
²⁰ Royal Observatory of Belgium, Ringlaan 3, 1180 Brussels, Belgium
²¹ INAF – Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
²² Institute of Astronomy, University of Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, UK
²³ Department of Physics and Astronomy, Division of Astronomy and Space Physics, Uppsala University, Box 516, 75120 Uppsala, Sweden
²⁴ Dipartimento di Fisica e Astronomia, Sezione Astrofisica, Università di Catania, via S. Sofia 78, 95123 Catania, Italy
²⁵ ASI Science Data Center, via del Politecnico SNC, 00133 Roma, Italy
²⁶ Laboratoire Lagrange (UMR 7293), Université de Nice Sophia Antipolis, CNRS, Observatoire de la Côte d’Azur, CS 342293, 06304 Nice Cedex 4, France
²⁷ Department for Astrophysics, Nicolaus Copernicus Astronomical Center, ul. Rabiańska 8, 87-100 Toruń, Poland
²⁸ Institut d’Astronomie et d’Astrophysique, Université libre de Brussels, boulevard du Triomphe, 1050 Brussels, Belgium
²⁹ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany

Received: 11 February 2014
Accepted: 19 March 2014

Abstract

The Gaia-ESO Survey is a large public spectroscopic survey that aims to derive radial velocities and fundamental parameters of about 10⁵ Milky Way stars in the field and in clusters. Observations are carried out with the multi-object optical spectrograph FLAMES, using simultaneously the medium-resolution (R ~ 20 000) GIRAFFE spectrograph and the high-resolution (R ~ 47 000) UVES spectrograph. In this paper we describe the methods and the software used for the data reduction, the derivation of the radial velocities, and the quality control of the FLAMES-UVES spectra. Data reduction has been performed using a workflow specifically developed for this project. This workflow runs the ESO public pipeline optimizing the data reduction for the Gaia-ESO Survey, automatically performs sky subtraction, barycentric correction and normalisation, and calculates radial velocities and a first guess of the rotational velocities. The quality control is performed using the output parameters from the ESO pipeline, by a visual inspection of the spectra and by the analysis of the signal-to-noise ratio of the spectra. Using the observations of the first 18 months, specifically targets observed multiple times at different epochs, stars observed with both GIRAFFE and UVES, and observations of radial velocity standards, we estimated the precision and the accuracy of the radial velocities. The statistical error on the radial velocities is σ ~ 0.4 km s^-1 and is mainly due to uncertainties in the zero point of the wavelength calibration. However, we found a systematic bias with respect to the GIRAFFE spectra (~0.9 km s^-1) and to the radial velocities of the standard stars (~0.5 km s^-1) retrieved from the literature. This bias will be corrected in the future data releases, when a common zero point for all the set-ups and instruments used for the survey is be established.