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D.E. Harker (UC San Diego/CASS), C.E. Woodward (University of Minnesota), D.H. Wooden (NASA Ames Research Center), M.S. Kelley (University of Minnesota)
Comet nuclei are the frozen reservoirs of dust and ices from the early solar nebula. In particular, the silicate mineralogy extant in the early solar nebula are recorded in the dust properties of comets. Of all solar system bodies, long period (LP) comets suffered the least post-formation alteration, thus variations in their grain properties probe the range of processes contributing to the dust reservoir in the early solar nebula. The composition of LP comet nuclei are probed through observations of the coma species.
We present mid-IR observations of two LP comets: C/2001 Q4 (Neat) and C/2002 T7 (Linear). For both comets, we obtained 7.8 -- 13.5~\micron\ spectrophotometric observations using the NASA IRTF (+MIRSI) on 2005 June 4 -- 2005 June 6 UT. During the time of the observations, Q4 was at a heliocentric distance of about 1~AU and T7 was at a distance of 1.1~AU. Q4 shows a silicate resonance feature due to small silicate dust grains, similar to earlier observations on 2005 May 11 UT (Wooden et al.\ 2004, ApJ, 612, L77). T7 shows a very weak silicate resonance feature implying that the thermal emission from the dust in the coma of T7 was dominated by grains larger than those in Q4. We also obtained high spatial resolution 10 and 20~\micron\ images of T7 using Gemini-S (+T-ReCS) on 2004 July 20 UT to map the distribution of dust grains in the coma. We will present our preliminary modeling results of the dust grains in comets Q4 and T7.
We acknowledge support from the NSF and NASA.
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Bulletin of the American Astronomical Society, 36 5
© 2004. The American Astronomical Society.