Characterization of STARDUST target comet 81P/Wild 2 from 1996 to 1998

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Abstract
We present the results of our monitoring of comet 81P/Wild 2, the target of the Stardust mission. Broad-band filter images and medium resolution spectra of this comet obtained along its pre- and postperihelion orbit between 1996 and 1998 were analysed in terms of coma morphology and activity. The morphological coma investigation revealed the presence of long-lasting fan structures, which remained essentially unchanged for at least three months. The () and () colour indices were determined at three different positions along the orbit. The two-dimensional analysis showed a uniform colour over the entire coma. Hence, the material composing the structures is not different from that of the underlying coma. The distribution of coma brightness as a function of projected distance from the nucleus shows no peculiarities. The evolution of the comet's activity during the pre- and postperihelion phase appears to be asymmetric in that activity increases faster preperihelion than it decreases postperihelion. The production rates (or their upper limits in the case on a non-detection) of CN, C2, C3, and NH2 were determined from the spectrophotometric observations and compared to other values published in the literature.