Abstract. Observation of close encounters of asteroids is a powerful method to determine their masses. A systematic search of such close encounters of asteroids with diameters larger than 40 km has been made thanks to a procedure to select the most efficient phenomena by means of the observable gravitational deflection. This study allows us to give lists of such single (one encounter) and multiple (several encounters between two pairs of asteroids) phenomena that will be observable from ground based astrometric telescopes from 2003 to 2022. We also give lists of single and multiple phenomena spanning 2010-2022 and implying less sensitive deflections only accessible by space astrometry. These last encounters may be observed during the ESA GAIA space mission.

Abstract. In order to evaluate a possible rotation between the Hipparcos and the dynamical reference frames, Hipparcos minor planets preliminary data are analysed. The resolution of the problem is very sensitive to correlations induced by the short length of the interval of observation. Several statistical methods are performed to appreciate the factors of bad conditioning. A procedure for variable selection and model building is given.