High-Resolution Thermal-IR Observations of Comet C/1995 O1 Hale-Bopp
P. V. Sada (CAM), D. E. Jennings, D. C. Reuter, and G. H. McCabe (NASA-GSFC)
We have performed high-resolution ( 
/ 
10,000) spectroscopic observations of comet C/1995 O1 Hale-Bopp at
selected thermal-infrared wavelengths on February 18-20, 1997.
We used CELESTE, a Goddard-developed cryogenic
echelle spectrometer, in conjunction with the McMath-Pierce Solar
Telescope (NSO/NOAO) at Kitt Peak National Observatory.
In particular we observed the 966-968 cm 
(10.34 
m) spectral
region, looking for evidence of CO 
and NH 
gas line emission
from the coma of the comet. The R(6) and R(8) overtone lines of CO
(966.250 and 967.707 cm respectively) are good detection
candidates because they are well populated level transitions at 100 K,
and because the Doppler velocity line shift (about -31 km/s at the
time) separates comet transitions from weak telluric absorption lines.
Although NH is no longer considered an abundant species in
cometary nuclei, we searched for it because non-LTE calculations
(Weaver and Mumma 1984, ApJ 276, 782) predict that 10%
of the entire 
band emission is concentrated on a single
line (sQ(3,3) at 967 cm ) in the same bandpass.
We also looked for the 
Q 
branch molecular
emission of C H 
at 822.3 cm (12.16 m).
This molecule has recently been detected in the near-IR on comet
C/1996 B2 Hyakutake (Mumma et al. 1996, Science 272, 1310).
In both instances a strong dust emission continuum from the comet's coma was detected. However, no molecular emission nor absorption features were detected superimposed on this continuum to our sensitivity limits. These observations place constraints on the temperature and composition of the gas within the coma.