the excitation temperature of the . Since mask 1 points lie at the periphery of the regions of high extinction and greater molecular column density (as witnessed by the detection of  in each mask 2 pixel), they encompass lower column density gas which is presumably characterized by lower volume density. Therefore we cannot assume that LTE applies as it does in mask 2. Approximately half of the mask 1 positions have an excitation temperature $\le$ 7.5 K, and if in LTE the gas would have to be unusually cold. It is thus reasonable to assume that this gas is subthermally excited. To analyze positions in mask 1 we use a simple excitation/radiative transfer analysis employing a spherical cloud large velocity gradient (LVG) code to compute the line intensities [e.g. @snell1981; @goldsmith1983]. We are using an LVG model largely as a tool to characterize the effect of trapping, which is important for excitation of CO at lower density. We do not believe it necessarily represents any statement about the detailed kinematics of the gas. The sensitivity of our results to the details of the velocity field should be quite small.

We have assumed that the kinetic temperature of the mask 1 