Structure of a thermally supercritical core. The figure shows the CO abundance, mean extinction, and gas density of a model cloud with the parameters of a thermally supercritical core. The model cloud is a BE sphere similar to that in Fig. 5 of Keto & Field (2005). The lowest curve is the log of the relative CO abundance. A value of zero represents no reduction in CO abundance from photodissociation or depletion. The middle curve is the transmission of starlight. A value of 1 represents no extinction and zero represents total extinction. The top curve is the log of the number density. Although the maximum radius on the plot is 0.6 pc, the core would not be observed to have this extent because of the low density and molecular abundance at large radii. Parameters are listed in Table 1.