MODELS FOR DENSE MOLECULAR CLOUD CORES

We present a detailed theoretical model for the thermal balance, chemi stry, and radiative transfer within quiescent dense molecular cloud co res that contain a central protostar, In the interior of such cores. w e expect the dust and gas temperatures to be well coupled, while in th e outer regions CO rotational emissions dominate the gas cooling and t he predicted gas temperature lies significantly below the dust tempera ture. Large spatial variations in the gas temperature are expected to affect the gas phase chemistry dramatically in particular, the predict ed water abundance varies by more than a factor of 1000 within cloud c ores that contain luminous protostars. Based upon our predictions for the thermal and chemical structure of cloud cores, we have constructed self-consistent radiative transfer models to compute the line strengt hs and line profiles for transitions of (CO)-C-12, (CO)-C-13, (CO)-O-1 8, ortho-and para-(H2O)-O-16, ortho-and para-(H2O)-O-18, and O I. We c arried out a general parameter study to determine the dependence of th e model predictions upon the parameters assumed for the source. We exp ect many of the far-infrared and submillimeter rotational transitions of water to be detectable either in emission or absorption with the us e of the infrared Space Observatory (ISO) and the Submillimeter Wave A stronomy Satellite. Quiescent, radiatively heated hot cores are expect ed to show low-gain maser emission in the 183 GHz 3(13)-2(20) water li ne, such as has been observed toward several hot core regions using gr ound-based telescopes. We predict the P-3(1)-P-3(2) fine-structure tra nsition of atomic oxygen near 63 mu m to be in strong absorption again st the continuum for many sources. Our model can also account successf ully for recent ISO observations of absorption in rovibrational transi tions of water toward the source AFGL 2591.