High-Resolution Optical Spectra of the Head of the Comet C/1996 B2 (Hyakutake)

Abstract

On 23 and 27 March 1996, we obtained high-resolution (R ≃ 26,000) échelle spectra by manually guiding on the head of Comet C/1996 B2 (Hyakutake). The two spectra cover different but slightly overlapping sets of 9 disjoint 70-Å regions of the green, yellow, and red. The continuum signal-to-noise ratio is in the range 40--100 per spectral resolution element. We used line lists from the standard astronomical literature to identify lines of [O I], Na I, C2, NH2, CN, and H2O+, we unsuccessfully sought evidence for CO+, and we obtained upper limits on HCO line strengths. In addition, we used laboratory data to make new identifications, by wavelength coincidence only, of lines of NH2. For the lines that remain unidentified, we have listed measured wavelengths and relative fluxes, in order to aid future efforts at identification. Our spectra include the green and one of the red lines of [O I], and the indicated photon flux ratio of λ 5577 / (λ 6300 + λ 6364) is in the range 0.12 to 0.16, consistent with formation of the excited O atoms from photodissociation of H2O.