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J. P. Morgenthaler, F. Scherb, C. W. Anderson, F. L. Roesler (UW--Madison), R. J. Oliversen (GSFC), N. E. Doane (Raytheon STX), W. H. Smyth (AER), M. L. Marconi (FPRI)
The exceptional brightness and long observational window of comet Hale-Bopp provided a remarkable opportunity to study both the neutral coma and the plasma in the coma and ion tail. Our team of observers from UW--Madison and Goddard Space Fight Center used seven different instruments at Kitt Peak to measure cometary emission from H, OH, O, H2O+, NH2, C, CN, C2, and the continuum. Here we present observations and model analysis for the O(1D) ([O~I]~6300~Å) emission. On 6 nights the Hydra positioner of the 3.5-meter WIYN Telescope Multi Object Spectrograph (MOS) was used to place up to 96 fibers in concentric rings from the nucleus to as much as 22.5 arc minutes in radius. On 4 nights a 7 by 13 array of 3 arc second fibers on 4 arc second centers known as Densepak was used on WIYN to probe the inner coma. On three nights, the 6-inch Fabry-Perot spectrometer that comprises the Wisconsin H-\alpha Mapper (WHAM), recorded narrow band images over a 1\circ field of view. On 29 nights a 2-inch Fabry-Perot spectrometer on the NSO McMath-Pierce main telescope recorded high resolution (\lambda/\Delta\lambda = 80,000) spectra of the [O~I]~6300~Å~emission with a 6~arcminute field of view. The combination of MOS and Fabry-Perot data covers spatial scales ranging from 2,000~km to 1 \times 106~km. The data consistently show a tailward asymmetry in the [O~I] emission. Previous comets with oxygen produced by photodissociation of H2O have shown spherically symmetric [O~I] emission which has been well described by the Monte Carlo Particle Trajectory Model (MCPTM) of Combi and Smyth (1988) with recent refinements by Combi, Bos, & Smyth (1993). We use this model to fit regions of the [O~I] distribution away from the tailward enhancements and find that the excess emission in the tailward direction is of order tens of Rayleighs at 500,000~km from the nucleus on March 5, 1997. We discuss several possible mechanisms for creating this emission asymmetry.
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