High Resolution Infrared Spectroscopy of Comet Hale-Bopp

T.Y. Brooke (JPL), H.A. Weaver (JHU), G. Chin (NASA/GSFC), S.J. Kim (Kyunghee U.)

High resolution spectra of comet Hale-Bopp (C/1995 O1) in the 2-5 tex2html_wrap_inline17 m region obtained during UT 2-5 March 1997 revealed emission lines of the gas-phase molecules CH tex2html_wrap_inline19 , C tex2html_wrap_inline21 H tex2html_wrap_inline23 , HCN, C tex2html_wrap_inline21 H tex2html_wrap_inline21 , H tex2html_wrap_inline21 O, and CO. The spectra were obtained at the NASA Infrared Telescope Facility, Mauna Kea, Hawaii, using CSHELL, an imaging spectrometer with a spectral resolving power of tex2html_wrap_inline31 . The comet's heliocentric and geocentric distances were 1.0 AU and 1.5AU, respectively, on 2 March.

Based on a preliminary analysis of spectra taken near 3.0 tex2html_wrap_inline17 m on 2 March, the P8-P11 lines of HCN and the P7 line of C tex2html_wrap_inline21 H tex2html_wrap_inline21 have been detected. The estimated rotational temperature of HCN is tex2html_wrap_inline43 K, which we assume is valid for C tex2html_wrap_inline21 H tex2html_wrap_inline21 as well. Estimated production rates at the nucleus were tex2html_wrap_inline49 sec tex2html_wrap_inline51 for both molecules. Using a water production rate of tex2html_wrap_inline53 sec tex2html_wrap_inline51 on 1.8 March, calculated from infrared emission lines (Dello Russo et al. IAUC 6604, 26 March 1997), we derive relative abundances of tex2html_wrap_inline59 % with respect to water for both HCN and C tex2html_wrap_inline21 H tex2html_wrap_inline21 .

OH lines were also detected and NH tex2html_wrap_inline21 lines were probably present. In addition, there was an emission feature which we have not yet identified at a rest wavenumber of 3286.57 cm tex2html_wrap_inline51 , which was also present in Hyakutake.