ASTROMETRY OF MINOR PLANETS WITH HIPPARCOS

After the processing of 30 months of the observations carried out by H ipparcos it is possible to provide a reliable idea of the astrometric results to be obtained on the 48 minor planets included in the observi ng programme. Hipparcos observations are one-dimensional measurements of the separation of objects along a precessing scanning circle, these scanning circles are averaged over approximately 0.3 day yielding a r eference great circle. The main output will consist of about 100 astro metric abscissae on a reference great circle for each minor planet wit h an individual accuracy of about 0.02 arcsec. We discuss in this pape r the reduction procedure and assess the systematic errors due to the shape and scattering properties of the asteroids. The use of the resul ts to improve the orbital parameters of the minor planets as well as t he link of the kinematical and dynamical frames is briefly touched upo n in the last section.