The Gaia-ESO Survey: Empirical determination of the precision of stellar radial velocities and projected rotation velocities^⋆,⋆⋆

¹ Astrophysics Group, Keele University, Keele, Staffordshire ST5 5BG, UK
e-mail: r.j.jackson@keele.ac.uk
² Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, CB3 0HA, UK
³ Moscow MV Lomonosov State University, Sternberg Astronomical Institute, 119992 Moscow, Russia
⁴ INAF–Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Florence, Italy
⁵ Research School of Astronomy & Astrophysics, Australian National University, Cotter Road, Weston Creek, ACT 2611, Australia
⁶ Rudolf Peierls Centre for Theoretical Physics, Keble Road, Oxford, OX1 3NP, UK
⁷ GEPI, Observatoire de Paris, CNRS, Université Paris Diderot, 5 place Jules Janssen, 92190 Meudon, France
⁸ Centre for Astrophysics Research, STRI, University of Hertfordshire, College Lane Campus, Hatfield AL10 9AB, UK
⁹ Lund Observatory, Department of Astronomy and Theoretical Physics, Box 43, 221 00 Lund, Sweden
¹⁰ Institute of Astronomy, University of Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, 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 de Astrofísica de Canarias, 38205, La Laguna, Tenerife, Spain
¹⁸ Universidad de La Laguna, Dept. Astrofísica, 38206, La Laguna, Tenerife, Spain
¹⁹ Royal Observatory of Belgium, Ringlaan 3, 1180 Brussels, Belgium
²⁰ INAF–Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
²¹ Department of Physics and Astronomy, Uppsala University, Box 516, 751 20 Uppsala, Sweden
²² Dipartimento di Fisica e Astronomia, Sezione Astrofisica, Università di Catania, via S. Sofia 78, 95123 Catania, Italy
²³ ASI Science Data Center, Via del Politecnico SNC, 00133 Roma, Italy
²⁴ Laboratoire Lagrange (UMR 7293), Université de Nice-Sophia Antipolis, CNRS, Observatoire de la Côte d’Azur, CS 34229, 06304 Nice Cedex 4, France
²⁵ Department for Astrophysics, Nicolaus Copernicus Astronomical Center, ul. Rabiańska 8, 87–100 Toruń, Poland
²⁶ Institut d’Astronomie et d’Astrophysique, Université libre de Brussels, Boulevard du Triomphe, 1050 Brussels, Belgium
²⁷ Instituto de Física y Astronomiía, Universidad de Valparaiíso, Chile
²⁸ European Southern Observatory, Alonso de Cordova 3107 Vitacura, Santiago de Chile, Chile
²⁹ INAF–Osservatorio Astrofisico di Catania, via S. Sofia 78, 95123 Catania, Italy
³⁰ Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool L3 5RF, UK
³¹ Departamento de Ciencias Físicas, Universidad Andrés Bello, República 220, 837-0134 Santiago, Chile
³² Millennium Institute of Astrophysics, Av. Vicuña Mackenna 4860, 782-0436 Macul, Santiago, Chile
³³ Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, 782-0436 Macul, Santiago, Chile
³⁴ Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal

Received: 2 April 2015
Accepted: 25 May 2015

Abstract

Context. The Gaia-ESO Survey (GES) is a large public spectroscopic survey at the European Southern Observatory Very Large Telescope.

Aims. A key aim is to provide precise radial velocities (RVs) and projected equatorial velocities (vsini) for representative samples of Galactic stars, which will complement information obtained by the Gaia astrometry satellite.

Methods. We present an analysis to empirically quantify the size and distribution of uncertainties in RV and vsini using spectra from repeated exposures of the same stars.

Results. We show that the uncertainties vary as simple scaling functions of signal-to-noise ratio (S/N) and vsini, that the uncertainties become larger with increasing photospheric temperature, but that the dependence on stellar gravity, metallicity and age is weak. The underlying uncertainty distributions have extended tails that are better represented by Student’s t-distributions than by normal distributions.

Conclusions. Parametrised results are provided, which enable estimates of the RV precision for almost all GES measurements, and estimates of the vsini precision for stars in young clusters, as a function of S/N, vsini and stellar temperature. The precision of individual high S/N GES RV measurements is 0.22–0.26 km s^-1, dependent on instrumental configuration.