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[38.04] Homing in on the period of 9P/Tempel

M.J.S. Belton (Belton Space Exploration Initiatives, LLC), K.J. Meech (Institute for Astronomy, University of Hawaii)

Since 1997 the Deep Impact mission has been engaged in an international program to determine the physical parameters of the nucleus of 9P/Tempel 1 (Meech et al. 2000). So far the size and albedo (Fernandez et al., 2003; mean radius = 2.6±-0.2 km, R-band geometric albedo = 0.072±0.016) and the mean colors (Meech et al., in preparation; B-V =0.744±0.012, V-R=0.475±0.004, R-I = 0.473±0.005) have been determined. The program involves nine observatories and has produced data between 1997-2002. This data set has been fully reduced and collected into a computerized database and studies of the nucleus phase function and dust production are underway. We report progress in understanding the spin of the nucleus. The R-band light curve covers both active (r <4 AU with coma) and inactive phases (beyond 4 AU) and yields 557 data points suitable for rotation analysis. Data taken when the comet was between 4.1--4.8AU yields H_R(1,1,0)=14.62±0.02 which, with the mean radius gives p_R=0.064±0.016. The data suggest a peak-to-valley amplitude of ~1 mag that indicates a minimum nucleus axial ratio of 2.5. Two periodicities emerge from analysis of the data beyond 4 AU: 1.148 and 2.149 inverse days. One of these is clearly an alias of the true frequency with diurnal sampling. We are working to distinguish the true periodicity by model fitting of the details of the lightcurve. In addition the amplitude of the light curve is observed to change by a factor of ~2 in the data beyond 4 AU. Through modeling we expect to put constraints on the pole direction.

Fernandez et al. 2003. Icarus, in press.

Meech et al. 2000. In ASP Conf. Ser, ed. G. Lemarchand & K. Meech 213, 235-242.

This work was supported through UMD and UH subcontracts Z667702, awarded under prime contract NASW-00004 from NASA.

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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.