Gaia Data Release 2

Summary of the variability processing and analysis results

¹ Department of Astronomy, University of Geneva, Ch. des Maillettes 51, 1290 Versoix, Switzerland
e-mail: Berry.Holl@unige.ch
² Department of Astronomy, University of Geneva, Ch. d’Ecogia 16, 1290 Versoix, Switzerland
³ SixSq, Rue du Bois-du-Lan 8, 1217 Geneva, Switzerland
⁴ GÉPI, Observatoire de Paris, Université PSL, CNRS, Place Jules Janssen 5, 92195 Meudon, France
⁵ INAF – Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Gobetti 93/3, 40129 Bologna, Italy
⁶ Instituut voor Sterrenkunde, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
⁷ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
⁸ Large Synoptic Survey Telescope, 950 N. Cherry Avenue, Tucson, AZ 85719, USA
⁹ Università di Catania, Dipartimento di Fisica e Astronomia, Sezione Astrofisica, Via S. Sofia 78, 95123 Catania, Italy
¹⁰ INAF – Osservatorio Astrofisico di Catania, Via S. Sofia 78, 95123 Catania, Italy
¹¹ University of Vienna, Department of Astrophysics, Tuerkenschanz-strasse 17, 1180 Vienna, Austria
¹² Department of Geosciences, Tel Aviv University, Tel Aviv 6997801, Israel
¹³ Dipartimento di Fisica e Astronomia, Università di Bologna, Via Piero Gobetti 93/2, 40129 Bologna, Italy
¹⁴ Departamento de Astrofísica, Centro de Astrobiología (INTA-CSIC), PO Box 78, 28691 Villanueva de la Cañada, Spain
¹⁶ INAF – Osservatorio Astronomico di Capodimonte, Via Moiariello 16, 80131 Napoli, Italy
¹⁵ School of Physics and Astronomy, Tel Aviv University, Tel Aviv 6997801, Israel
¹⁷ Departamento de Inteligencia Artificial, UNED, C/ Juan del Rosal 16, 28040 Madrid, Spain
¹⁸ Department of Astrophysics/IMAPP, Radboud University, PO Box 9010, 6500 GL Nijmegen, The Netherlands
¹⁹ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching b. München, Germany
²⁰ Laboratoire d’astrophysique de Bordeaux, Université Bordeaux, CNRS, B18N, allée Geoffroy Saint-Hilaire, 33615 Pessac, France
²¹ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
²² Royal Observatory of Belgium, Ringlaan 3, 1180 Brussels, Belgium
²³ Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences, Konkoly Thege Miklós út 15-17, 1121 Budapest, Hungary
²⁴ Department of Astronomy, Eötvös Loránd University, Pázmány Péter sétány 1/a, 1117 Budapest, Hungary
²⁵ Villanova University, Department of Astrophysics and Planetary Science, 800 Lancaster Avenue, Villanova, PA 19085, USA
²⁶ Faculty of Mathematics and Physics, University of Ljubljana, Jadranska ulica 19, 1000 Ljubljana, Slovenia
²⁷ Academy of Sciences of the Czech Republic, Fricova 298, 25165 Ondrejov, Czech Republic
²⁸ Baja Observatory of University of Szeged, Szegedi út III/70, 6500 Baja, Hungary
²⁹ Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, Bd de l’Observatoire, CS 34229, 06304 Nice cedex 4, France
³⁰ CENTRA FCUL, Campo Grande, Edif. C8, 1749-016 Lisboa, Portugal
³¹ EPFL SB MATHAA STAP, MA B1 473 (Bâtiment MA), Station 8, 1015 Lausanne, Switzerland
³² Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warszawa, Poland
³³ Institute of Theoretical Physics, Faculty of Mathematics and Physics, Charles University in Prague, Prague, Czech Republic
³⁴ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany

Received: 23 February 2018
Accepted: 28 May 2018

Abstract

Context. The Gaia Data Release 2 (DR2) contains more than half a million sources that are identified as variable stars.

Aims. We summarise the processing and results of the identification of variable source candidates of RR Lyrae stars, Cepheids, long-period variables (LPVs), rotation modulation (BY Dra-type) stars, δ Scuti and SX Phoenicis stars, and short-timescale variables. In this release we aim to provide useful but not necessarily complete samples of candidates.

Methods. The processed Gaia data consist of the G, G_BP, and G_RP photometry during the first 22 months of operations as well as positions and parallaxes. Various methods from classical statistics, data mining, and time-series analysis were applied and tailored to the specific properties of Gaia data, as were various visualisation tools to interpret the data.

Results. The DR2 variability release contains 228 904 RR Lyrae stars, 11 438 Cepheids, 151 761 LPVs, 147 535 stars with rotation modulation, 8882 δ Scuti and SX Phoenicis stars, and 3018 short-timescale variables. These results are distributed over a classification and various Specific Object Studies tables in the Gaia archive, along with the three-band time series and associated statistics for the underlying 550 737 unique sources. We estimate that about half of them are newly identified variables. The variability type completeness varies strongly as a function of sky position as a result of the non-uniform sky coverage and intermediate calibration level of these data. The probabilistic and automated nature of this work implies certain completeness and contamination rates that are quantified so that users can anticipate their effects. Thismeans that even well-known variable sources can be missed or misidentified in the published data.

Conclusions. The DR2 variability release only represents a small subset of the processed data. Future releases will include more variable sources and data products; however, DR2 shows the (already) very high quality of the data and great promise for variability studies.