GaiaEarly Data Release 3

Abstract

Context. GaiaEarly Data Release 3 (GaiaEDR3) contains results for 1.812 billion sources in the magnitude rangeG= 3–21 based on observations collected by the European Space AgencyGaiasatellite during the first 34 months of its operational phase.Aims.We describe the input data, the models, and the processing used for the astrometric content ofGaiaEDR3, as well as the validation of these results performed within the astrometry task.Methods.The processing broadly followed the same procedures as forGaiaDR2, but with significant improvements to the modelling of observations. For the first time in theGaiadata processing, colour-dependent calibrations of the line- and point-spread functions have been used for sources with well-determined colours from DR2. In the astrometric processing these sources obtained five-parameter solutions, whereas other sources were processed using a special calibration that allowed a pseudocolour to be estimated as the sixth astrometric parameter. Compared with DR2, the astrometric calibration models have been extended, and the spin-related distortion model includes a self-consistent determination of basic-angle variations, improving the global parallax zero point.Results. GaiaEDR3 gives full astrometric data (positions at epoch J2016.0, parallaxes, and proper motions) for 1.468 billion sources (585 millionwith five-parameter solutions, 882 million with six parameters), and mean positions at J2016.0 for an additional 344 million.Solutions with five parameters are generally more accurate than six-parameter solutions, and are available for 93% of the sources brighter than the 17th magnitude. The median uncertainty in parallax and annual proper motion is 0.02–0.03 mas at magnitudeG= 9–14, and around 0.5 mas atG= 20. Extensive characterisation of the statistical properties of the solutions is provided, including the estimated angular power spectrum of parallax bias from the quasars.