P. Charlot

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: In this article, the authors report on follow-up observations to study the multiwavelength emission in the post-outburst phase of 3C 454.3 and ascribe this redder-when-brighter behaviour to the presence of a ''little blue bump'' due to line emission from the broad line region, which is clearly visible in the source spectral energy distribution (SED) during faint states.

TL;DR: In this paper, the authors present and analyse the WEBT multifrequency observations of 3C 454.3 in the 2007-2008 observing season, including XMM-Newton observations and near-IR spectroscopic monitoring, and compare the recent emission behaviour with the past one.

TL;DR: In this article, the first parallax measurements of the primary standard candles of the cosmological distance ladder, that involve astrometry collected by Gaia during the initial 14 months of science operation, are published in Gaia Data Release 1 (DR1) as part of the Tycho-Gaia Astrometric Solution (TGAS).

TL;DR: In this paper, the authors describe the properties of the Gaia auxiliary quasar solution for a subset of sources matched to ICRF2, and compare their optical and radio positions at the sub-mas level.