High-temperature molecular cores near massive stars and application to the Orion hot core

We calculate the temperature structure of hot, high column density, molecular cores for several assumed density distributions, with either internal or external illumination. We show that large (N[H-2] greater than or similar to 10(23) cm(-2)), warm (T greater than or similar to 100 K) columns of molecular gas are more easily produced when cores are heated from within than when cores are heated externally. We compare our results to the conditions inferred from recent high-resolution observations of the Orion hot core. We find that external heating by the star at the center of the SiO maser disk (radio source "I") may partially heat the nearby core, but heating of the more extended (similar to 10'') hot core likely arises due to a young star (or stars) embedded in the core. We show that high and low-mass cores have physical parameters that lie on a common plane defined by their mass, luminosity and temperature and that we may use such information to determine the physical size of embedded cores even from measurements that do not resolve the structure of a particular core.