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L. A. McFadden, C. J. Crockett, M. F. A'Hearn (U. Maryland), M. J. S. Belton (Belton Space Exploration Initiatives), T. L. Farnham (U. Maryland), K. P. Klaasen (JPL, Caltech), J. Y. Li (U. Maryland), C. M. Lisse (APL/Johns Hopkins University), J. M. Sunshine (SAIC), D. D. Wellnitz (U. Maryland)
We have analyzed the color sequences of the medium resolution imager on board the Deep Impact spacecraft as it approached Comet Tempel 1 for impact on July 4, 2005. The imager carried 9 filters; two clear filters, two 100 nm wide filters, one centered at 750, the other at 950 nm, and five cometary filters; two for dust and three emission band filters at 309 nm (OH) 387 nm (CN), and 514 nm (C2). Images are processed with the team’s calibration pipeline data processing routine (Klaasen et al. 2005). In images examined 577 to 67 s before impact, the images in filters longward of 514 nm that cover the C2 band as well as a continuum band and two broadband context filters at 750 and 950 nm, reveal an enhancement of flux by a factor of 2, extending in a halo, ~5 km from the center of the nucleus. Images are registered to sub-pixel scale by translating, rotating and magnifying a selected image to visually match a reference image. Ratioed images at different wavelengths show the I/f of the nucleus to have a spectral slope of 0.12/1000 angstroms between 350-950 nm with no absorption bands. Ratioed images show reflectance variations of a factor of two, but only in small discrete regions, relative to the average nucleus, with visible wavelength albedo of 0.04. Comparison of the coma before and after impact reveals color differences that may reflect grain size differences in the ejecta plume. This work is supported by the NASA Discovery Mission, Deep Impact.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.