The Chemical Composition and Evolution of Giant Molecular Cloud Cores: A Comparison of Observation and Theory

摘要

We present the results of an observational and theoretical study of the chemical composition and evo- lution of three giant cloud cores in Orion A, M17, and Cepheus A. This study is the culmination of a chemical survey of 32 transitions of 20 different molecules and isotopic variants in these cloud cores. Using these data, combined with observationally derived physical conditions, chemical abundances were calculated for several positions in each cloud. A global analysis of the molecular abundances shows that, although abundance differences exist, the chemical composition of giant cloud cores is remarkably homogeneous. This agreement suggests that the chemical evolution of the individual giant cloud cores is not unique.