Determination of molecular gas properties using methyl cyanide lines

摘要

A survey of 27 galactic star-forming regions in the 6_K-5_K, 5_K-4_K, and 8_K-7_K CH3CN lines at 110, 92, and 147 GHz, respectively, is made. Twenty-five sources are detected at 110 GHz, nineteen at 92 GHz, and three at 147 GHz. The strongest CH3CN emission arise in hot cores in the regions of massive star formation. CH3CN abundance in these objects is larger than 10^(-9) due to grain mantle evaporation. Weaker CH3CN lines are found in a number of sources. They may arise either in warm (30-50 K) dense (10^(5)-10^(7) cm^(-3)) clouds, or in hot regions accompanied by colder gas.