Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998baas...30.1065a&link_type=abstract
American Astronomical Society, DPS meeting #30, #29.P16; Bulletin of the American Astronomical Society, Vol. 30, p.1065
Astronomy and Astrophysics
Astronomy
Scientific paper
The 3.5-meter WIYN Telescope and its Multi-Object Spectrograph (MOS)obtained simultaneous spectra at many points in the coma of Comet Hale-Bopp 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 6100 Angstroms to 6400 Angstroms with resolution of approximately 15,000. This spectral region contains the emission features of H_2O(+) . From these data we have extracted the radial velocity of the H_2O(+) . We find the acceleration in the anit-sun direction to be of the order of 20 cm sec(-) (2) . The measured velocity fields have been compared to full 3D MAUS-MHD models. The models suggest that the degree ofconfinement of the coma and the velocities attained in the anti-sun 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 anti-sun direction are more like those produced by a fast solar wind. The observations were obtained at a time when Hale-Bopp 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.
Anderson Martha C.
Combi Michael R.
Gombosi Tamas
Hansen Kenneth Calvin
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