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Karen Jean Meech -- Comet Rotation |
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General Comet Rotation CharacteristicsNot only is knowledge of the global physical properties of comets important for the understanding of the early solar system accretion models (i.e. how big did the nuclei grow), but the nucleus size, albedo and rotational periods are critical parameters which affect the solar energy distribution on the surface which will dictate the nature of a comet's activity. We have information about the nucleus properties of only a couple dozen comets, in part because when they are inactive and it is possible to observe the nucleus without contamination from the coma, the nucleus is far from the sun, hence faint, and requires large telescopes. Part of my research program is to study the physical properties of the nuclei. Various aspects of the program have been done in collaboration with Marc Buie (Lowell Observatory), Olivier Hainaut (Institute for Astronomy), Michael Belton, Nalin Samarasinha and Beatrice Mueller (NOAO), along with several others). Below is a summary of general nucleus properties from a paper which was presented as an invited paper on "Physical Properties of Comets" at the ACM 96 meeting in Versailles, France (submitted to Advances in Space Research).
Summary of Recent work on 46P/Wirtanen![]() Onset of Activity - From a composite lightcurve made from our data and other published data, it is apparent that the activity on the comet began between 3.5-4.5 AU. In the images at the right, showing data from 1996 June, August and November, coma is clearly evident in the August data (r = 2.5 AU). The coma extended to greater than 18,000 km during August 1996 (middle image) and 25,000 km in November (bottom image). Nucleus Rotation Period - We have observed a periodic variation in the light curve of 3.8 hours which we interpret as the brightness modulation caused by a nucleus rotating (see Figure) with a period near 7.6 hours. Nucleus Axis Ratio and Size - Using the HST estimate of the nucleus radius (0.58 km) and the rate at which the surface brightness decreased in brightness (slopes of -1.6 and -1.4 in August and November, respectively), we were able to deduce the range of brightness variations that the comet would have if there were no coma. We found that the bare nucleus axis ratio should have been a:b = 1.7 for a low albedo nucleus.
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Last modified: February 4, 2001 | |
Karen Meech Institute for Astronomy 2680 Woodlawn Drive Honolulu, HI 96822 meech@ifa.hawaii.edu |
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