Detecting Influential Points in the Hipparcos Minor Planets


M-L. Bougeard (1)(2), J-F. Bange (3), A. Bec-Borsenberger(3)

(1) URA CNRS 1125, Observatoire de Paris, 61 av. de l'Observatoire, 75014 Paris,
      France. 

(2) Universite Claude Bernard, LYON I, France.

(3) Service de Mecanique Celeste du Bureau des Longitudes, URA CNRS 707,
	77 avenue Denfert-Rochereau 75014 Paris, France.

ABSTRACT
The observations of minor planets are of particular interest for determining the
equinox and a possible rotation between the Hipparcos and the dynamical
reference frames. 
In order to evaluate these unknowns, Hipparcos data are compared to the values
calculated from the equations of motion. The satellite's observations are
related to intermediate reference frames called Reference Great Circle (RGC).
The associated equations of condition involve in addition the orbital elements
and dynamical parameters (such as masses of minor planets, etc.). 
Here, several statistical methods are performed in order to detect
observationnal points having a high statistical influence on the global Least
Squares fit. That concerns the effects of the given RGC, as well as those of the
minor planets included in the LS resolution. We show in addition the importance
of the "normal points" preliminary determination.