Near-Infrared Spectroscopy of Molecules and Radicals from Comet C/1996 B2 Hyakutake

Details Near-Infrared Spectroscopy of Molecules and Radicals from Comet C/1996 B2 Hyakutake Near-Infrared Spectroscopy of Molecules and Radicals from Comet C/1996 B2 Hyakutake

Sep 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996dps....28.0915b&link_type=abstract

American Astronomical Society, DPS meeting #28, #09.15; Bulletin of the American Astronomical Society, Vol. 28, p.1091

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Scientific paper

High resolution spectra of comet Hyakutake in the 3 mu m region revealed a host of gas emission lines including CH_4 and C_2H_6 (Mumma et al., Science 272, 1310, 1996), C_2H_2 and HCN (Brooke et al., Nature, in press). Our spectra were obtained on Apr. 8.2 and 9.2 1996 UT at the NASA Infrared Telescope Facility, Mauna Kea, Hawaii with CSHELL at a spectral resolution of 2 x 10(4) . The comet was roughly r=0.7 AU from the sun and Delta =0.5 AU from Earth. The effective spatial resolution was a few hundred km and the slit extended to ~ 5000 km from the nucleus. Estimated abundances relative to H_2O were 0.3--0.9% for C_2H_2 and 0.2--0.6% for HCN for an assumed H_2O production rate range of 1.5--3 x 10(29) sec(-1) . The nominal rotational temperatures of both molecules in the inner coma were relatively high ~ 100-150 K, though they have large uncertainties. Ethylene, C_2H_4, the other C_2-containing hydrocarbon, was searched for but not detected. A preliminary upper limit on the production rate is <3 x 10(27) sec(-1) or <2% relative to H_2O. A model of the solid-state abundances in cold molecular clouds (Hasegawa & Herbst, MNRAS 263, 589, 1993) gives rough agreement with the Hyakutake abundances for the C_2 hydrocarbons and predicts very low C_2H_4. Numerous lines of OH were detected. Two pairs of lambda -doubled emission lines near 3.04 mu m had different spatial distributions: the v=2--1 P_1(7/2) lines were very extended, as expected for fluorescence, but the v=1--0 P_2(13/2) lines were more peaked at the nucleus and may result primarily from rapid prompt emission by OH left in excited states following the photodissociation of H_2O. Emission lines of NH_2 near 3.24 mu m were also seen for the first time. This radical is well known in the visible. There remain some as yet unidentified lines in the spectra.

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