On the use of HIPPARCOS data for the determination of astrometric positions of outer planets

Abstract

We investigated the improvement of observed astrometric positions of outer planets by use of Hipparcos Catalogue stars and satellite measurements. Positions of Jupiter from photographic plates were obtained, indirectly, from measurements of the Galilean satellites, using the G5 ephemerides of Bureau des Longitudes. The use of Hipparcos data in the astrometric reductions resulted in positions with an external rms error of 42 mas in right ascension, and 38 mas in declination, which is 5-10 times better than current or classical techniques. Furthermore, with such precision, poorly known instrumental characteristics can be studied, such as the anisotropy of the scale. Finally, an important impact on the fit of planetary ephemerides to the optical observations is expected.