The Future of Optical Reference Systems
Résumé
Optical reference frames have been traditionally limited in astrometric accuracy compared to radio reference frames which have long reached a sub-milliarcsecond accuracy. The next decade holds promises for big changes in this area with the launch of the Gaia space astrometric mission which unlike Hipparcos will be able to observe several hundred thousands of extragalactic objects with an astrometric accuracy of a few tens of microarcseconds. After reviewing the current status of optical and radio reference frames, this paper draws prospects for building the Gaia optical frame and its alignment with the current International Celestial Reference Frame (ICRF) which is based on radio-interferometric measurements.