CO, H₂CO, and CH₃OH in comet 2002 C1 Ikeya-Zhang

Comet 2002 C1 Ikeya-Zhang was observed on seven dates post-perihelion between UT 2002 March 21.9 (R_h = 0.51 AU) and April 13.9 (R_h = 0.78 AU), using the Cryogenic Echelle Spectrometer (CSHELL) at the NASA Infrared Telescope Facility. Emission lines from carbon monoxide (CO), formaldehyde (H₂CO) and methanol (CH₃OH) were observed on multiple dates at high spectral resolution. The small pixel size yielded spatially-resolved emission profiles. This permitted us to reliably measure rotational temperatures (for CO) and production rates along the slit, and to assess the nature of the release (ie, native vs. extended source) of these three molecules. Here we present preliminary results for CO and CH₃OH from one date (April 13.7-13.9), and for H₂CO from three dates (April 11.7-13.7). Our retrieved rotational temperature for CO (115 ± 8 K) was based on the intensities of eight lines. Our measured mixing ratios were CO / H₂O = (4.7 ± 0.8) × 10^-2 and CH₃OH / H₂O = (2.5 ± 0.5) × 10^-2 on April 13, and H₂CO / H₂O = (0.62 ± 0.18) × 10^-2 for the 3-day mean. The spatial profiles for all three molecules were consistent with release solely from the nucleus.