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Astron. Astrophys. 335, 757-764 (1998)


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Model of the nongravitational motion for Comet 32P/Comas Solá

Magorzata Królikowska , Grzegorz Sitarski and Sawomira Szutowicz

Space Research Center of the Polish Academy of Sciences, Bartycka 18A, PL-00716 Warsaw, Poland

Received 10 December 1996 / Accepted 27 March 1998

Abstract

The nongravitational motion of the periodic comet Comas Solá is studied on the basis of positional observations made during nine consecutive revolutions around the Sun. Nongravitational effects in the comet motion have been examined for Sekanina's forced precession model of the rotating nucleus. We present three models which successfully link all the 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: [FORMULA] connected with the rotating comet nucleus, [FORMULA] and s describing the precession of spin-axis of the nucleus, and two constant time shifts [FORMULA] and [FORMULA]. The last two parameters describe displacements of the maximum value of the known function [FORMULA] with respect to the perihelion time. The best solution was obtained assuming that between the apparitions of 1935 and of 1944 the time shift changed its value, thus [FORMULA] and [FORMULA] refer to apparitions before and after 1940 Jan. 1, respectively. Variations of angles I and [FORMULA] with time, describing the nucleus spin-axis orientation, are presented. It appears that forced precession causes 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 observations. The obtained models give some strong constraints on the physical parameters of the nucleus of comet P/Comas Solá. Assuming a prolate spheroid for the nucleus of the comet, the expected rotational period is [FORMULA] hours for an equatorial radius of 2 km. For the same radius, the oblate Model II gives the much smaller rotational period of [FORMULA] hours. The polar radii are 2.2 km and 1.3 km for the prolate and oblate model, respectively.

Key words: comets: individual: 32P/Comas Solá

Send offprint requests to: G. Sitarski, (sitarski@cbk.waw.pl)

© European Southern Observatory (ESO) 1998

Online publication: June 18, 1998

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