Change in the Rotational Period of Comet P/Tempel 2 between the 1988 and 1994 Apparitions

ISSN： 0019-1035

Source： Icarus, Vol.123, Iss.2, 1996-10, pp. : 463-477

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Abstract

Comets often exhibit activity on their surface in the form of jets. These jets in turn should influence the rotational state of the nucleus, producing torques that may increase or decrease the period. We have attempted to detect such changes in the rotational state of comet P/Tempel 2 since the preperihelion observations of its last apparition in 1988. This object's side-real period had been determined by Sekanina (1991) to be 8 h 55 m 55 s .2 ±0 s .2 for the 1988 data. CCD observations of P/Tempel 2 made with the 0.9 m telescope on Kitt Peak within a time span of 2 months (October and December 1994), postperihelion, show that the rotational period of this object has changed by a small but significant fraction. Fourier transform methods as well as numerical lightcurve models for the nucleus of P/Tempel 2 are used in the analysis of our data. We find five possible periods for this apparition (8 h 52 m 37 s , 8 h 54 m 29 s , 8 h 56 m 21 s , 8 h 58 m 14 s , 9 h 00 m 07 s ) which are distinctively different from the period found by Sekanina (1991) for the previous apparition. Due to aliasing, we cannot choose among these five periods. These periods represent both spin-up and spin-down solutions. The minimal period change is 26 sec ± 10 sec. Future observations during the next apparition preperihelion, using better sampling, should easily confirm and constrain our result. This is the first direct evidence for a period change based on nuclear lightcurves of a comet. We also discuss Comet Levy (1990c) and the Great Comet of 1744, for which changes in periodicity have been reported in the literature.