AN OBSERVATIONAL TEST FOR THE NUMERICAL-MODELS OF MOTION OF 2 PERIODIC COMETS

Numerical models of the nongravitational motion for two periodic comet s, P/Grigg-Skjellerup and P/Kopff, were published by the author in 199 1 and 1994. The models of motion, successfully linking all the apparit ions of the comets, included nongravitational effects according to the Marsden's method based on the rotating and precessing cometary nucleu s. Both comets were rediscovered during their new returns to the Sun. It is shown that the models of motion excellently represent the curren t comets' observations: the RMS residuals for several astrometric obse rvations are less that 1'' and no systematic trends in the residuals a re observed.