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T.L. Farnham (Univ. Maryland), B.E.A. Mueller (NOAO/PSI), M.M. Knight (Univ. Maryland), N.H. Samarasinha (NOAO/PSI)
We obtained monthly observations of comet Tempel~1 at the Kitt Peak National Observatory, in support of the Deep Impact mission. Using the HB narrowband comet filters, we obtained images between January and June 2005, including six nights of observations in April that can be phased to provide complete coverage of the 40.7-hour rotation phase. Our goal was to monitor the comet in the months leading up to the DI encounter, to characterize its behavior for mission planning, and to provide a baseline against which the post-impact activity could be compared. We also obtained images in the days around the DI encounter, to determine how the comet's activity was affected by the impact.
Our pre-impact images show a dust morphology dominated by a strong jet to the south of the orbital plane. This feature changes only gradually in the months leading up to impact, with no variation correlating with the 40.7-hour rotation period. During impact, a massive outburst is seen, with residual dust visible for several days before the coma returns to its pre-impact state. More interestingly, images obtained with the CN filter reveal at least one CN jet that appears to change with the comet's 40.7-hour rotation period. Variations are detectable as early as April, but the features become much more well-defined in the June and July observations and persist after the DI event. A preliminary analysis indicates that, following the impact, the CN brightness increased much less than the continuum and dissipated more rapidly, suggesting that the material excavated by the impact had a high dust-to-gas ratio. Furthermore, the lack of long-term changes in the comet suggests that the impact did not create a significant new source of dust or CN.
We will report on a more complete analysis of our observations, including gas production rates and measurements of Af\rho, a proxy for dust production. We will attempt to put these results into context with the information obtained from the Deep Impact spacecraft.
This research has been funded by the Deep Impact project, under the NASA grant NASW 00004.
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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.