Astrometric star catalogues as combination of Hipparcos/Tycho catalogues with ground-based observations

Abstract

The successful ESA mission Hipparcos provided very precise parallaxes positions and proper motions of many stars in optical wavelength. Therefore it is a primary representation of International Celestial Reference System in this wavelength. However, the shortness of the mission (less than four years) causes some problems with proper motions of the stars that are double or multiple. Therefore, a combination of the positions measured by Hipparcos satellite with ground-based observations with much longer history provides a better reference frame that is more stable in time. Several examples of such combinations are presented (ACT, TYCHO-2, FK6, GC+HIP, TYC2+HIP, ARIHIP) and briefly described. The stress is put on the most recent Earth Orientation Catalogue (EOC) that uses about 4.4 million optical observations of latitude/universal time variations (made during the twentieth century at 33 observatories in Earth orientation programmes), in combination with some of the above mentioned combined catalogues. The second version of the new catalogue EOC-2 contains 4418 objects, and the precision of their proper motions is far better than that of Hipparcos Catalogue.

Keywords

• astrometry
• catalogs
• reference systems