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L.M. Woodney (UCF/Lowell Observatory), D.G. Schleicher (Lowell Observatory)
Resonant flourescence is the dominate process behind the observed molecular emission lines in comets. Line intensities within a molecular band can vary greatly due to both the properties of the solar radiation which pumps the flourescence process and physical properties of the gas. Doppler displacement of cometary lines relative to the solar Fraunhofer features due to the comet's velocity relative to the sun results in a variation in intensity of the comet lines known as the Swings effect. Further variations in molecular line intensities are induced by bulk motions of the gas within the cometary coma (known as the Greenstein effect), by collisions which can thermalize the populations of the various rotational levels, and non-equilibrium processes such as creation of the observed ``daughter'' molecules in high rotational levels due to excess energy available during the dissociation of the parent molecule. Each of these additional effects depend on the location within the coma, along with various physical properties of the comet, such as outgassing rates, ionization rates, and the presence of jets. As a result, detailed fluorescence modeling of observed spectra can reveal a great deal about physical properties of the coma.
Echelle spectra of C/Hyakutake (1996 B2) were obtained at the Kitt Peak 4-m Mayall Telescope on March 16, 1996, the night of it's very close (0.11 AU) approach to Earth. Spectra were taken on nucleus and at three offset positions, giving a unique look at the coma at both high spatial and spectral resolutions. The slit size of 0.87'' \times 0.74'' corresponds to 68 \times 580 km at the comet. The slit integrated spectra have previously appeared in Meier et al. (1998, Icarus 136, 268-279). In the current examination of these data we have modeled the flourescence and collisional quenching of the column integrated OH band at each of the four slit locations (on-nucleus, 2'', 7'' and 10'' offsets). Best fit models reveal that the observed OH has a velocity of approximately 1 km/s and is 65 to 75% quenched. This is consistent with the outflow velocity determined by Combi et al. (1999, ApJ 512,961-968) from CN, C2, NH2 and O(1D) spectra. We are currently doing flourescence modeling of the NH and CN bands, and any new results on these molecules will be presented.
This research is supported by NASA.
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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.