C. Dolding

TL;DR: Gaia as discussed by the authors is a cornerstone mission in the science programme of the European Space Agency (ESA). The spacecraft construction was approved in 2006, following a study in which the original interferometric concept was changed to a direct-imaging approach.

TL;DR: The first Gaia data release, Gaia DR1 as discussed by the authors, consists of three components: a primary astrometric data set which contains the positions, parallaxes, and mean proper motions for about 2 million of the brightest stars in common with the Hipparcos and Tycho-2 catalogues.

TL;DR: In this paper, the authors describe the validation and properties of the median radial velocities published in GDR2 and evaluate the accuracy of the selected sample with respect to ground-based catalogues.

TL;DR: In this paper, the authors describe the validation and properties of the median radial velocities published in Gaia DR2, which provide a full-sky coverage and are complete with respect to the astrometric data to within 77.2% (for G ≤ 12.5 mag).

TL;DR: The first Gaia Data Release contains the Tycho-Gaia Astrometric Solution (TGAS) component by means of the astrometric data for open clusters as discussed by the authors, which is a subset of about 2 million stars for which, besides the position and photometry, the proper motion and parallax are calculated using Hipparcos and Tycho 2 positions in 1991.