Celestial Reference System, High Precision Astrometry

In the domain of astrometry, SYRTE is involved in the realization of the International Celestial Reference Frame (ICRF) which is necessary to know with optimal precision the location of all the bodies in the Universe. One of the tasks consists in establishing the coordinates of quasars as accurately as possible. These quasars are assumed to provide fixed (quasi-inertial) directions in space, which make it possible to determine the coordinates of moving objects: stars in galactic rotation, planets and asteroids rotating around the sun etc... Because of the increasing number of sources in the catalogues of quasars, it is necessary to make their intercomparison as well as the analysis of the extremely accurate observation data obtained by very long baseline interferometry (VLBI) in the radio domain, or by CCD images in the focal plan of large telescopes at optical wavelengths.

Another research theme is the link between the International Celestial Reference System and the dynamical system represented by the trajectories of the mobile bodies in the solar system. At SYRTE, the analysis of lunar laser ranging data, of pulsar chronometry, and the use of optical observations lead to the determination of this link.