A model for clumpy giant molecular clouds with external ultraviolet heating

A model of clumpy molecular clouds based on that of Kwan and Sanders (1986) has been developed, in which a clump filling factor which is very low at the cloud surface and increases to about 1 at the cloud center allows the UV radiation from an H II region located at the surface to permeate the volume of the cloud and to create a temperature gradient and varying abundance of CO within each clump. The model is in general agreement with the enhanced intensity of the (C-12)O J = 3-2 transition relative to the J = 1-0 line observed throughout the central 10-arcmin region of the Orion molecular cloud. 28 refs