MODEL OF THE NONGRAVITATIONAL MOTION FOR COMET 32P COMAS SOLA/

The nongravitational motion of the periodic comet Comas Sola is studie d on the basis of positional observations made during nine consecutive revolutions around the Sun. Nongravitational effects in the comet mot ion have been examined for Sekanina's forced precession model of the r otating nucleus. We present three models which successfully link all t he observed apparitions of the comet during 1926-1996. Two solutions ( Models II and III) represent oblate spheroids and the third one (Model I)- a prolate spheroid (nucleus rotation around its longer axis). We have determined values of eight parameters: A, eta , I, phi connected with the rotating comet nucleus, f(p) and s describing the precession of spin-axis of the nucleus, and two constant time shifts tau(1) and t au(2) The last two parameters describe displacements of the maximum va lue of the known function g(r) with respect to the perihelion time. Th e best solution was obtained assuming that between the apparitions of 1935 and of 1944 the time shift changed its value, thus tau(1) and tau (2) refer to apparitions before and after 1940 Jan. 1, respectively. V ariations of angles I and phi with time, describing the nucleus spin-a xis orientation, are presented. It appears that forced precession caus es the moderate changes of the position of the rotation axis in space. The ratio of rotational period to radius of the nucleus was found for each model. The present precession models are in agreement with sizes and periods of rotation of other cometary nuclei deduced from observa tions. The obtained models give some strong constraints on the physica l parameters of the nucleus of comet P/Comas Sola. Assuming a prolate spheroid for the nucleus of the comet, the expected rotational period is 14 +/- 4 hours for an equatorial radius of 2 km. For the same radiu s, the oblate Model II gives the much smaller rotational period of 2.4 +/- 0.4 hours. The polar radii are 2.2 km and 1.3 km for the prolate and oblate model, respectively.