The Abundance of Atomic Carbon near the Ionization Fronts
نویسندگان
چکیده
We have observed the 492 GHz ground-state line of atomic carbon in the edge-on ionization fronts in M17 and .s1~0. y.te find that, contrary to expectation, the C I emission peaks farther into the molecular cloud from t~e Iomza~IO~ fro~t than does the CO. In fact the peak C I abundance in M17 occurs more than 60 mag of visual extmctton mto the cloud from the ionization front. Calculations of the ratio of C I to CO column densities yiel? values of 0.1--0.2. These observations do not support chemical models which predict that neutral atomic carbon should be found only near the edges of molecular clouds. Other models are discussed which may explain the observations. Subject headings: interstellar: abundances interstellar: matter nebulae: abundances nebulae: individual
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