Relative motions of fragments of the split comets: II. Separation velocities and differential decelerations for extensively observed comets

A multiparameter model has been devised to discriminate the effects of the velocity of separation of two fragments of a split comet on their observed motions from the effects of the postsplit differential nongravitational forces. The iterative differential-correction procedure is applied to five extensively observed split comets: West 1975n, Ikeya-Seki 1965 VIII, Wirtanen 1957 VI, the Southern Comet 1947 XII, and Periodic Brooks 2 1889 V. The present model confirms that the major contribution to the observed rate of separation of the fragments comes from the postsplit forces. The model removes or substantially reduces the systematic trends in the residuals of comets West, Wirtanen, and P/Brooks 2, which could not be eliminated by a simple model that ignored the effects of the separation velocity. In particular, the results for Comet Wirtanen now indicate that the comet split at a heliocentric distance of more than 9 AU and that the initial rate of separation of the two fragments did not amount to more than 26 cm/sec. The separation velocities for the other comets range from 1 to 2 m/sec. Difficulties of the interpretation of the observed separation velocities are briefly discussed.