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M. A. DiSanti (Catholic U. at GSFC), M. J. Mumma (GSFC), N. Dello Russo (Catholic U. at GSFC), K. Magee-Sauer (Rowan University), R. Novak (Iona College)
The volatile organic composition of the long-period comet C/1999 T1 (McNaught-Hartley) was studied at infrared wavelengths on several dates post-perihelion using CSHELL at the IRTF and NIRSPEC at Keck 2. The heliocentric distance varied from R= 1.27 AU on UT 2001 January 13 to 1.71 AU on March 05. High-resolution spectra were obtained (lambda / Delta-lambda ~ 15,000 - 20,000), revealing emissions from water, carbon monoxide, ethane, methane, methanol, and hydrogen cyanide, as well as OH prompt emission. Preliminary results indicate a substantial CO mixing ratio (CO:H2O = 0.15 - 0.20). Owing to the relatively small nod distance between A and B beams (~ 12 - 15 arc-seconds along slit), this is primarily a measure of the native CO production rate. This CO abundance is similar to the native CO mixing ratio we find for C/1996 B2 (Hyakutake), and somewhat higher than that measured for C/1995 O1 (Hale-Bopp), 0.12. It is substantially higher than that measured for 3 other Oort Cloud comets contained in our sample (C/1999 H1 Lee, C/1999 S4 Linear, and C/2001 A2 Linear), for which CO:H2O was a few percent or less. Mixing ratios measured for other species in C/1999 T1 were more closely in line with those found in the other comets sampled. A summary of production rates, and implications for the formation of C/McNaught-Hartley will be presented. This work was supported by the NASA Planetary Astronomy Program through Grants NAG5-7905 and RTOP 344-32-30-07.