Thermal emission from BOK globules

Abstract

Models of the thermal emission from dust within Bok globules are developed, assuming the heat source is the interstellar radiation field (IRF) and accurately solving the radiative-transfer problem using the half-range moment method in spherical geometry. The models are characterized by the central optical depth, the dust density distribution, and the grain type. The FIR flux spectrum and surface-brightness profile are calculated. The primary interest is in the thermalization efficiency of globules. Only globules containing amorphous dust grains are able to convert the incident IRF into FIR emission with the high efficiency implied by the observations. However, this is incompatible with the observed FIR emission with the high efficiency implied by the observations. However, this is incompatible with the observed spectra, which indicate the presence of crystalline silicate grains. Perhaps these conclusions could be reconciled by the addition of an internal radiant heat source, such as a protostar. This would also explain why many globules appear to emit more photons than they can possibly absorb from the IRF. 32 references.