Sensitivity record in space
Spatial astrometry is well and truly a world-renowned European speciality. It rapidly developed under the impetus of the French astrophysicist Pierre Lacroute (1906-1993), who succeeded in convincing the ESA of the interest of developing the Hipparcos satellite to measure the position and the motion of the stars. This was done by Astrium with the instrumentation already being tested at CSL. Gaia’s development followed the same path. It has gone a step further than Hipparcos, which was used between 1990 and 1993, by making even sharper observations than its predecessor.
Gaia double silicon carbide telescope is more sensitive (*) and is currently equipped with 106 CCD detectors to generate a billion pixels. Not only will Gaia observe a billion stars in the Milky Way, up to a magnitude of 20 (i.e. 1 % of the content of our galaxy) at high precision (1000 times better than Hipparcos, its predecessor from the 1980s); it will also repeat its measurements between 60 and 150 times during its five years in operation, leading to the creation of a 3-D map of the vault of heaven. It will also be responsible for observing half a million quasars and revealing 15,000 exoplanets...
Once it has been validated as operational by ESOC (European Space Operations Centre) in Darmstadt, the European astrometry observatory will be transferred to the community of astronomers and astrophysicists. Determined within the framework of the Horizon 2000+ scientific programme (6th cornerstone), Gaia is the fruit of an investment costing almost EUR 1 billion (launch and positioning included, as well as the five years of operations). There is an additional 300 million for data processing. Approximately 400 researchers belong to DPAC (Data Processing & Analysis Consortium). Since 2007, they have been mobilised for the development of Gaia’s data processing software, data that will amount to hundreds of teraoctets! Belgium is ranked 7th (out of 18) in this consortium; 45 people, with the support of Belspo and the FNRS among others, devote their time to the Gaia mission.
Double involvement of AGO
The Gaia observatory will not provide direct images but will give hitherto unseen indications on the distance of stars, thus allowing their apparent flux to be converted into intrinsic luminosity. ![CCD array assembling]( "CCD array assembling.")
An initial catalogue of observations is expected for the beginning of the next decade. Within DPAC, several researchers from the University of Liège play an essential role in the processing of Gaia's measurements. It is important to interpret the data received through three specific channels: the astrometric channel, which provides the position of the stars and therefore their distance; the photometric channel, which gives access to the colours of the stars to define their characteristics; and the spectroscopic channel, which concerns the brightest stars in order to measure their radial velocity. In the AGO Department at the University of Liège, members of two research units are in the front line to exploit at best Gaia’s observations.
