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

[62.07] High-resolution Optical Spectra of the Head of Comet C/1996 B2 (Hyakutake)

N. D. Morrison, D. Knauth, C. L. Mulliss, W. B. Lee (U. Toledo)

Cometary spectra are well known to include many unidentified lines (e. g., Wyckoff and Heyd 1992, BAAS 24, 1126). Since comets are usually observed at modest spectral resolution, the precise information on wavelengths and band structure that is needed to make a laboratory identification is often lacking. Therefore, we obtained high-resolution spectra of Comet Hyakutake primarily in order to study unidentified features.

We observed Comet Hyakutake on 23 and 27 March 1996 for integration times of 120 and 105 minutes, respectively, with the 1-m telescope and the fiber-fed échelle spectrograph of Ritter Observatory. The detector is a 1200 \times 800-pixel EEV CCD mounted in a Wright Instruments, Inc. LN_2-cooled dewar. The spectral resolution of our material is 0.23 Å\ at \lambda5800, and the signal-to-noise ratio in the dust-scattered continuum is in the range 20--50. The two spectra cover different but slightly overlapping sets of 9 disjoint 70-Å\ regions in the green, yellow and red. Since flux calibration is not possible for our apparatus, the spectra have been normalized to the continuum.

In addition to the spectrum of reflected sunlight, numerous emission features are present, including unresolved, apparently single, lines; a broad, symmetrical feature with no evident structure; and various molecular bands. Since we guided on the comet's brightest region, our data may be biased against ionic features, which are enhanced in the plasma tail. Species identified so far include Na I, [O I], NH_2, and C_2.

Line identifications will be presented, as well as a detailed list of unidentified features with absolute wavelength accuracies on the order of \pm 0.1 Å\ or better.

Program listing for Wednesday