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Session 15 - Structure and Collapse of Molecular Clouds: Theory.
Display session, Monday, January 13
We present results from a theoretical study of the temperature structure of dense molecular cores heated either internally or externally by massive stars. This study has been motivated largely by observations of the Orion "Hot Core." Interpretation of line and continuum data suggests that the Hot Core has column densities N(H_2\sim 10^24\,cm^-2 and temperature above 200 K. Recent observations (Gezari et al. 1992; Dougados et al. 1993; Menten amp; Reid 1995; Plambeck 1995) have called into question early speculation that the Hot Core was illuminated externally. Our modeling results suggest that to get such large column densities to such high temperatures requires illumination by an embedded source. Observations of other hot cores show that these conditions are typical. We focus our study on the relationship between the luminosity of a heating source, the physical structure of the core which is heated, and the location of the heating source relative to the core. We suggest that hot cores represent sites of high-mass star formation where even the early ultra-compact HII region phase of evolution is not visible. Our calculations quantitatively show that internally heated cores have larger columns of hot gas than externally illuminated cores, and that, therefore, millimeter, submillimeter, and infrared measurements of large columns of hot gas can help pinpoint the location of deeply embedded massive protostars. We show how various molecular tracers may be used to distinguish between internally and externally illuminated cores.
Program listing for Monday