Gaia Data Release 2

Properties and validation of the radial velocities

¹ GEPI, Observatoire de Paris, Université PSL, CNRS, 5 Place Jules Janssen, 92190 Meudon, France
e-mail: david.katz@obspm.fr
² Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, Surrey RH5 6NT, UK
³ Royal Observatory of Belgium, Ringlaan 3, 1180 Brussels, Belgium
⁴ Laboratoire Univers et Particules de Montpellier, Université Montpellier, CNRS, Place Eugène Bataillon, CC72, 34095 Montpellier Cedex 05, France
⁵ CNES Centre Spatial de Toulouse, 18 avenue Edouard Belin, 31401 Toulouse Cedex 9, France
⁶ CRAAG – Centre de Recherche en Astronomie, Astrophysique et Géophysique, Route de l’Observatoire Bp 63 Bouzareah, 16340 Alger, Algeria
⁷ Institut d’Astrophysique et de Géophysique, Université de Liège, 19c, Allée du 6 Août, 4000 Liège, Belgium
⁸ Universiteit Antwerpen, Onderzoeksgroep Toegepaste Wiskunde, Middelheimlaan 1, 2020 Antwerpen, Belgium
⁹ F.R.S.-FNRS, Rue d’Egmont 5, 1000 Brussels, Belgium
¹⁰ Thales Services for CNES Centre Spatial de Toulouse, 18 avenue Edouard Belin, 31401 Toulouse Cedex 9, France
¹¹ Department of Astronomy, University of Geneva, Chemin d’Ecogia 16, CH-1290 Versoix, Switzerland
¹² Leibniz Institute for Astrophysics Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
¹³ Laboratoire d’astrophysique de Bordeaux, Université de Bordeaux, CNRS, B18N, allée Geoffroy Saint-Hilaire, 33615 Pessac, France
¹⁴ Laboratoire Lagrange, Université Nice Sophia-Antipolis, Observatoire de la Côte d’Azur, CNRS, CS 34229, 06304 Nice Cedex, France
¹⁵ Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain
¹⁶ Universidad de La Laguna, Departamento de Astrofísica, 38206 La Laguna, Tenerife, Spain
¹⁷ Université Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
¹⁸ Max Plank Institute für Sonnensystemforschung, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
¹⁹ Unidad de Astronomía, Fac. Cs. Básicas, Universidad de Antofagasta, Avda. U. de Antofagasta 02800, Antofagasta, Chile
²⁰ ATOS for CNES Centre Spatial de Toulouse, 18 avenue Edouard Belin, 31401 Toulouse Cedex 9, France
²¹ Max Planck Institute for Extraterrestrial Physics, High Energy Group, Gießenbachstraße, 85741 Garching, Germany
²² Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
²³ LNE-SYRTE, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, 61 avenue de l’Observatoire, 75014 Paris, France
²⁴ Faculty of Mathematics and Physics, University of Ljubljana, Jadranska ulica 19, 1000 Ljubljana, Slovenia
²⁵ INAF-Osservatorio Astronomico di Padova, vicolo Osservatorio 5, 35122 Padova, Italy
²⁶ INAF Astronomical Observatory of Padova, 36012 Asiago (VI), Italy
²⁷ Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611, Australia

Received: 20 April 2018
Accepted: 12 December 2018

Abstract

Context. For Gaia DR2, 280 million spectra collected by the Radial Velocity Spectrometer instrument on board Gaia were processed, and median radial velocities were derived for 9.8 million sources brighter than G_RVS = 12 mag.

Aims. This paper describes the validation and properties of the median radial velocities published in Gaia DR2.

Methods. Quality tests and filters were applied to select those of the 9.8 million radial velocities that have the quality to be published in Gaia DR2. The accuracy of the selected sample was assessed with respect to ground-based catalogues. Its precision was estimated using both ground-based catalogues and the distribution of the Gaia radial velocity uncertainties. Results. Gaia DR2 contains median radial velocities for 7 224 631 stars, with T_eff in the range [3550, 6900] K, which successfully passed the quality tests. The published median radial velocities provide a full-sky coverage and are complete with respect to the astrometric data to within 77.2% (for G ≤ 12.5 mag). The median radial velocity residuals with respect to the ground-based surveys vary from one catalogue to another, but do not exceed a few 100 m s⁻¹. In addition, the Gaia radial velocities show a positive trend as a function of magnitude, which starts around G_RVS ~ 9 mag and reaches about + 500 m s⁻¹ at G_RVS = 11.75 mag. The origin of the trend is under investigation, with the aim to correct for it in Gaia DR3. The overall precision, estimated from the median of the Gaia radial velocity uncertainties, is 1.05 km s⁻¹. The radial velocity precision is a function of many parameters, in particular, the magnitude and effective temperature. For bright stars, G_RVS ∈ [4, 8] mag, the precision, estimated using the full dataset, is in the range 220–350 m s⁻¹, which is about three to five times more precise than the pre-launch specification of 1 km s⁻¹. At the faint end, G_RVS = 11.75 mag, the precisions for T_eff = 5000 and 6500 K are 1.4 and 3.7 km s⁻¹, respectively.