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C. M. Anderson (University of Wisconsin-Madison), M. R. Combi, T. Gombosi, K.C. Hansen (University of Michigan)
The 3.5meter WIYN Telescope and its MultiObject Spectrograph (MOS)obtained simultaneous spectra at many points in the coma of Comet HaleBopp between 1996 October and 1997 April. The "Hydra" fiber positioner was used to sample a ring pattern of points about the nucleus with a minimum spacing of 40 arc seconds and a maximum radius of 22.5 arc minutes. A integral field device called "Densepak" was also used to sample a 7 x 13 rectangular pattern of 91, 3 arc second fibers on 4 arc second centers. The bench spectrograph was used in the echelle mode with an interference filter to isolate a single order and covered the wavelength range from 6100Åto 6400Åwith resolution of approximately 15,000. This spectral region contains the emission features of H2O+. From these data we have extracted the radial velocity of the H2O+. We find the acceleration in the anitsun direction to be of the order of 20 cm sec2. The measured velocity fields have been compared to full 3D MAUSMHD models. The models suggest that the degree ofconfinement of the coma and the velocities attained in the antisun direction depend sensitively upon the velocity of the ambient solar wind. The observed velocity fields are consistent with the confinement of the near coma by a relatively slow solar wind while the speeds attained at distances of the order of a million kilometers in the antisun direction are more like those produced by a fast solar wind. The observations were obtained at a time when HaleBopp was at intermediate heliocentric latitudes where the solar wind speed is known to change rapidly from slow to fast modes. This situation is under further investigation.
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The author(s) of this abstract have provided an email address for comments about the abstract: anderson@astro.wisc.edu