CS MULTITRANSITIONAL STUDY OF DENSITY DISTRIBUTION IN STAR-FORMING REGIONS .2. THE S140 REGION

The S140 molecular cloud was observed in five transitions of CS with r esolutions of 11''-45''. The data were analyzed with both the LVG and microturbulent models of radiative transfer to derive the density stru cture. It was found that the CS emission comes from three components o f gas: a spherical component centered on the infrared cluster, an arc component along the ionization front between the S140 H II region and the dense molecular cloud core, and a high-velocity component from the dense part of a molecular outflow. The spherical component contribute s most to the CS emission and was analyzed in more detail than the oth er components. Using a temperature distribution derived from an analys is of the dust emission from S140, we fit a power-law density distribu tion of n(r) = n(i)(r/r(i))-alpha to the spherical component. The best fit was for n(i) = 1.4 x 10(6) (density at r(i) = 0.026 pc) and alpha = 0.8. The density (n(i)) was found to be greater than or equal to th e density required to account for the dust emission, depending on the dust opacity laws adopted. The presence of optical emission (Dinerstei n, Lester, & Rank 1979) suggests a clumpy structure for the dense gas. Considerations of the virial mass and the lowest amount of column den sity required to produce dust emission put the volume filling factor ( f(v)) of the dense gas at approximately 0.14-0.5. We compared S140 wit h other regions of star formation where the density structure has been derived from excitation analysis. Source-source variations in density gradients and clumpiness clearly exist, ranging from alpha = 2 and f( v) approximately 1 in B335 to alpha approximately 0, f(v) approximatel y 0.1 in M17. There is a tendency for more massive star-forming region s to have a flatter density distribution, a more clumpy structure, and a larger number of young stars. The implications of this tendency are discussed.