Maps of 92 GHz methyl cyanide emission in Orion-KL

We present 4 sec to 6 sec images of the methyl cyanide (CH3CN) J = 5K to 4K lines toward the Orion Kleinmann-Low (Orion-KL) region obtained with the Hat Creek millimeter interferometer. The morphology of the low-excitation lines closely follows the distribution of dust emission, while the higher-excitation lines are confined to a approximately 10 sec region near IRc2. Methyl cyanide emission is found associated with all of the previously recognized source substructures, including the hot core, CS1 condensation ('10 km/s feature'), compact ridge ('8 km/s feature'), western clump, extended ridge, and northwest filament. Methyl cyanide, like other symmetric top molecules, makes an excellent thermometer. Statistical equilibrium calculations constrain the temperature of the CS1 condensation to the range 52-83 K and the temperature of the southern ridge to the range 120-170 K. Dynamical interactions with the IRc2 outflow likely contribute to heating these regions. Much higher temperatures, approximately greater than 250 K, are indicated for the hot core, where the CH3CN abundance is enhanced by at least two orders of magnitude, presumably due to grain chemistry.