Astron. Astrophys. 363, 323-334 (2000)

1. Introduction

A faint comet, discovered photographically as a magnitude object on 1924 December 22 by M. Wolf at Heidelberg, was observed only for about one month. The following three successive returns of the comet to the Sun were lost for observations. After twenty seven years in October 1951 it was again rediscovered at Mt. Palomar Observatory by R. G. Harrington. The discovery was not immediately suspected as the return of Wolf 's comet. The identity of both comets has been proved after the 1957 apparition (Wisniewski 1964). With an orbital period of about 6.5 years, the Comet Wolf-Harrington belongs to the Jupiter family comets. The comet is in a chaotic orbit and approached Jupiter twice in 1936 and in 1948 what caused considerable changes in orbital parameters, especially in the perihelion distance and the eccentricity. Since 1952 it has been observed at every eighth return to perihelion.

The existence of a nongravitational anomaly in the comet motion between 1951 and 1965 has been noted by Sitarski (1970) and next confirmed by Marsden (1977) by linking observations from four apparitions. To link observations from the period 1951-1977 Sitarski (1981) assumed a constant secular change of the semi-major axis of the comet's orbit. The nongravitational acceleration over ten returns of the comet to the Sun, from 1924 to 1985, was investigated by Szutowicz (1987). It appeared that the motion of the comet is affected by variable nongravitational effects and an essential change of their pattern occured after 1978. The observations from seven comet's apparitions covering the period 1951-1991 were successfully linked assuming a linear precession of the cometary spin axis (Szutowicz 1992). However, the model seemed to be nonphysical because of extremaly fast rate of precession, especially in the angle related to the longitude of the Sun.

In the present paper the more detailed analysis of the nongravitational acceleration in the motion of comet 43P/Wolf-Harrington during its all apparitions is performed. The irregular character of the comet's nongravitational perturbations has been explained by changes in a surface distribution of the active areas (Sect. 4.4) and by a forced precession of the spin axis coupled with nonlinear shifts of the function with respect to the perihelion time (Sect. 4.3). Sect. 6.2 contains estimations of the effective active area. In Sect. 7 the size of the nucleus radius on the basis of orbital models and photometric observations is discussed.

© European Southern Observatory (ESO) 2000

Online publication: December 5, 2000
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