Session 62 - Comet Hyakutake Encounter.
Display session, Wednesday, June 12
Great Hall,

## [62.08] High-Resolution Observations of Comet Hyakutake (1996 B2): O (^1D)

A. L. Cochran, D. L. Lambert, W. D. Cochran (Univ. Texas)

We obtained observations of comet Hyakutake (1996\,B2) with the 2DCoude spectrograph on the McDonald Observatory 2.7-m telescope on 30 March 1996 UT. The observations were at a nominal resolving power of 185,000. The spectra included the O\,(^1D) (6300Åemission line from the comet. The doppler shift was sufficient to separate clearly the cometary emission line from the telluric oxygen line. The spectrograph entrance slit subtended 0.34\times8.2\,arcsec on the sky. A ThAr line had a width of approximately 3 pixels with this setup (FWHM=0.034Åwhile the cometary emission line was clearly resolved at \sim6 pixels. The O\,(^1D) emission arises from the photodissociation of H_2O, the dominant parent ice. The branching ratio to produce the oxygen (^1D) is approximately 7% of the photodissociations. The production of the oxygen emission line is by prompt emission. Thus, the width of the 6300Å\ O\,(^1D) line is a direct measure of the gas outflow velocity of the coma. We will present our observations of this emission line along with modeling of the data to derive the outflow velocity. These observations represent a unique opportunity to study a comet at such high spectral resolving power in order to accurately measure the line width.