Gaia Data Release 1

Astrometry: one billion positions, two million proper motions and parallaxes

¹ Lund ObservatoryDepartment of Astronomy and Theoretical Physics, Lund University, Box 43, 22100 Lund, Sweden
² ESA, European Space Astronomy Centre, Camino Bajo del Castillo s/n, 28691 Villanueva de la Cañada, Spain
³ Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstraße 14, 69120 Heidelberg, Germany
⁴ Lohrmann-Observatorium, Technische Universität Dresden, Mommsenstrasse 13, 01062 Dresden, Germany
⁵ HE Space Operations BV for ESA/ESAC, Camino Bajo del Castillo s/n, 28691 Villanueva de la Cañada, Spain
⁶ Vitrociset Belgium for ESA/ESAC, Camino Bajo del Castillo s/n, 28691 Villanueva de la Cañada, Spain
⁷ Telespazio Vega UK Ltd for ESA/ESAC, Camino Bajo del Castillo s/n, 28691 Villanueva de la Cañada, Spain
⁸ NASA/IPAC Infrared Science Archive, California Institute of Technology, Mail Code 100-22, 770 South Wilson Avenue, Pasadena, CA 91125, USA
⁹ Observatoire Astronomique de l’Université de Genève, Sauverny, Chemin des Maillettes 51, 1290 Versoix, Switzerland
¹⁰ Aurora Technology for ESA/ESAC, Camino Bajo del Castillo s/n, 28691 Villanueva de la Cañada, Spain
¹¹ The Server Labs S.L. for ESA/ESAC, Camino Bajo del Castillo s/n, 28691 Villanueva de la Cañada, Spain
¹² Istituto Nazionale di Astrofisica, Osservatorio Astrofisico di Torino, via Osservatorio 20, Pino Torinese, 10025 Torino, Italy
¹³ SYRTE, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, LNE, 61 avenue de l’Observatoire, 75014 Paris, France
¹⁴ GEA-Observatorio National/MCT, Rua Gal. Jose Cristino 77, 20921-400 Rio de Janeiro, Brazil
¹⁵ Universidade do Porto, Rua do Campo Alegre,687, 4169-007 Porto, Portugal
¹⁶ Institute of Astrophysics and Space Sciences Faculdade de Ciencias, Campo Grande, 1749-016 Lisboa, Portugal
¹⁷ INAF, Osservatorio Astrofisico di Catania, 95123 Catania, Italy
¹⁸ IMCCE, Institut de Mécanique Céleste et de Calcul des Ephémérides, 77 avenue Denfert-Rochereau, 75014 Paris, France
¹⁹ EURIX S.r.l., via Carcano 26, 10153 Torino, Italy
²⁰ Univ. Bordeaux, LAB, UMR 5804, 33270 Floirac, France
²¹ CNRS, LAB, UMR 5804, 33270 Floirac, France
²² Institut de Ciències del Cosmos, Universitat de Barcelona (IEEC-UB), Martí Franquès 1, 08028 Barcelona, Spain
²³ Institute for Astronomy, School of Physics and Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh, EH9 3HJ, UK
²⁴ University of Padova, via Marzolo 8, 35131 Padova, Italy
²⁵ Observatoire de la Côte d’Azur, BP 4229, 06304 Nice Cedex 4, France
²⁶ RHEA for ESA/ESAC, Camino Bajo del Castillo s/n, 28691 Villanueva de la Cañada, Spain
²⁷ Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Rd, 200030 Shanghai, PR China
²⁸ GMV for ESA/ESAC, Camino Bajo del Castillo s/n, 28691 Villanueva de la Cañada, Spain
²⁹ Astrophysics Research Institute, ic2 – Liverpool Science Park, 146 Brownlow Hill, Liverpool L3 5RF, UK
³⁰ ESA, European Space Research and Technology Centre, Keplerlaan 1, 2200 AG Noordwijk, The Netherlands
³¹ Gaia Project Office for DPAC/ESA, Camino Bajo del Castillo s/n, 28691 Villanueva de la Cañada, Spain
³² Praesepe for ESA/ESAC, Camino Bajo del Castillo s/n, 28691 Villanueva de la Cañada, Spain
³³ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany
³⁴ Las Cumbres Global Optical Telescope Network, 6740 Cortona Dr. 102, Goleta, CA 93117, USA
³⁵ Altec, Corso Marche 79, 10146 Torino, Italy

^⋆ Corresponding author: L. Lindegren, e-mail: lennart@astro.lu.se

Received: 14 April 2016
Accepted: 29 June 2016

Abstract

Context. Gaia Data Release 1 (DR1) contains astrometric results for more than 1 billion stars brighter than magnitude 20.7 based on observations collected by the Gaia satellite during the first 14 months of its operational phase.

Aims. We give a brief overview of the astrometric content of the data release and of the model assumptions, data processing, and validation of the results.

Methods. For stars in common with the Hipparcos and Tycho-2 catalogues, complete astrometric single-star solutions are obtained by incorporating positional information from the earlier catalogues. For other stars only their positions are obtained, essentially by neglecting their proper motions and parallaxes. The results are validated by an analysis of the residuals, through special validation runs, and by comparison with external data.

Results. For about two million of the brighter stars (down to magnitude ~11.5) we obtain positions, parallaxes, and proper motions to Hipparcos-type precision or better. For these stars, systematic errors depending for example on position and colour are at a level of ± 0.3 milliarcsecond (mas). For the remaining stars we obtain positions at epoch J2015.0 accurate to ~10 mas. Positions and proper motions are given in a reference frame that is aligned with the International Celestial Reference Frame (ICRF) to better than 0.1 mas at epoch J2015.0, and non-rotating with respect to ICRF to within 0.03 mas yr^-1. The Hipparcos reference frame is found to rotate with respect to the Gaia DR1 frame at a rate of 0.24 mas yr^-1.

Conclusions. Based on less than a quarter of the nominal mission length and on very provisional and incomplete calibrations, the quality and completeness of the astrometric data in Gaia DR1 are far from what is expected for the final mission products. The present results nevertheless represent a huge improvement in the available fundamental stellar data and practical definition of the optical reference frame.