The Spatial Excitation of Volatile Organics in Comet Hyakutake: Evidence for a Distributed Source of Carbon Monoxide Emission

Details The Spatial Excitation of Volatile Organics in Comet Hyakutake: Evidence for a Distributed Source of Carbon Monoxide Emission The Spatial Excitation of Volatile Organics in Comet Hyakutake: Evidence for a Distributed Source of Carbon Monoxide Emission

Sep 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996dps....28.0930d&link_type=abstract

American Astronomical Society, DPS meeting #28, #09.30; Bulletin of the American Astronomical Society, Vol. 28, p.1094

Astronomy and Astrophysics

Astronomy

Scientific paper

We present observations of comet C/1996 B2 (Hyakutake) near perigee (Delta ~ 0.1 AU) with the Cryogenic Echelle Spectrometer (CSHELL) at the NASA IRTF 3-m telescope on UT 1996 March 24.5. The instrument operates in the 1 - 5 mu m region, incorporating a 256x256 InSb detector array having 0.2('') pixels. We centered the comet in the 30('') long, 1('') wide slit, thereby obtaining spatial information out to ~ 10(3) km on either side of the nucleus with spatial resolution ~ 30 km, and with spectral resolving power nu / Delta nu ~ 2 x 10(4) . We chose our grating settings so as to target specific bands of key cometary volatiles, and we present the spatial distributions of carbon monoxide (CO), methane (CH_4) and ethane (C_2H_6). We emphasize spatial-spectral maps of emission lines in the v = 1-0 fundamental band of CO at ~ 4.7 mu m (nu ~ 2140 cm(-1) ). Our free spectral range (4.95 cm(-1) ) was such that two lines were included in our band pass for each grating position. We sampled all lower state rotational levels J = 0 through 6, and thus we have an accurate map of CO excitation in the inner coma. Our data show indisputable evidence for a distributed source of CO emission in the coma of comet Hyakutake, in addition to the direct nuclear (native) source. We also measured extended emission from the nu_3 R0 line (3028.75 cm(-1) ) of CH_4, and from the () rQ_0 (2983.4 cm(-1) ) and () rQ_1 (2986.7 cm(-1) ) branches of the nu_7 band of C_2H_6. The kinetic temperatures derived from CO can be used to constrain the excitation of these hydrocarbons as a function of distance from the nucleus. This work was supported by the Planetary Astronomy Program of the Research Programs Division, NASA, under RTOP 196-41-54 to MJM. MAD gratefully acknowledges supplemental support from the Planetary Astronomy Program for travel to the IRTF.

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