<i>Gaia</i> Data Release 2

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.

Affiliated Institutions

• KU Leuven BE
• Laboratoire d'Astrophysique de Bordeaux FR
• Villanova University US
• University of Cambridge GB
• University of Ljubljana SI
• Large Synoptic Survey Telescope Corporation US
• Astronomical Observatory of Capodimonte IT
• Czech Academy of Sciences CZ
• University of Geneva CH
• European Southern Observatory DE
• Centro de Astrobiología ES
• École Polytechnique Fédérale de Lausanne CH
• Université Côte d'Azur FR
• University of Vienna AT
• Centre National de la Recherche Scientifique FR
• National University of Distance Education ES
• University of Bologna IT
• Center for Astrophysics Harvard & Smithsonian US
• Tel Aviv University IL
• Osservatorio astronomico di Bologna IT
• Osservatorio di Astrofisica e Scienza dello Spazio
• Royal Observatory of Belgium BE
• Osservatorio Astrofisico di Catania IT
• Istituto Nazionale di Fisica Nucleare, Sezione di Catania IT
• Eötvös Loránd University HU
• Observatoire de la Côte d’Azur FR
• Charles University CZ
• Observatoire de Paris FR
• Bologna Research Area IT
• University of Warsaw PL
• Laboratoire du Futur FR
• Konkoly Observatory HU
• Hungarian Academy of Sciences HU
• Research Centre for Astronomy and Earth Sciences HU
• Université Paris Sciences et Lettres FR
• University of Szeged HU
• Max Planck Institute for Astronomy DE
• Radboud University Nijmegen NL

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