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T.L. Farnham (Univ. of Maryland), D.G. Schleicher (Lowell Obs.)
We will present results from our analysis of images and narrowband photometry of the Stardust spacecraft target comet 81P/Wild~2. We have images from 10~nights in 1997 and photometry from three apparitions: 4~nights in 1978, 5~nights in 1984 and 12~nights in 1997. All data were obtained at Lowell Observatory.
For the photometry measurements, narrowband filters were used to isolate the emissions from and compute the production rates for five gas species (OH, NH, CN, C2 and C3). Additional filters were used to isolate the continuum, from which A(\theta)f\rho, a proxy for the dust production, could be found. A preliminary analysis of this data indicates that both the OH and the dust exhibit significant pre-/post-perihelion asymmetries, with their production rates peaking 2-3 months before perihelion. The carbon-bearing species, on the other hand, have relatively flat production rates for several months on either side of perihelion. Wild~2 is also depleted in carbon-chain molecules with respect to CN. Finally, the dust is significantly reddened in the blue and UV; this reddening shows no obvious trends with heliocentric distance.
Our imaging data were obtained primarily with a broadband R filter, though some images were also obtained with narrowband filters. Simple image enhancement techniques reveal the presence of features in the coma in the months around perihelion. These features indicate that comet Wild~2 has isolated active regions on its surface, which could affect the Stardust spacecraft around the time of its closest approach. Using aperture photometry measurements from our images, we produced a lightcurve of Wild~2 that spans about seven hours. This lightcurve shows no obvious variation with time, indicating one of several possibilities: the nucleus is not highly elongated or is entirely overwhelmed by the coma; the sub-Earth and Sub-solar points were near the pole during the observations; or the rotation period is much longer than seven hours. We will utilize the lightcurve in combination with the features in the coma to further investigate the comet's rotation state.
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Bulletin of the American Astronomical Society, 34, #3< br> © 2002. The American Astronomical Soceity.