A MULTITRANSITION CO AND CS-(2-1) COMPARISON OF A STAR-FORMING AND A NON-STAR-FORMING GIANT MOLECULAR CLOUD

CO (3-2), CO (1-0), and CS (2-1) observations of clumps in the cold, l ow-luminosity cloud G216-2.5 discovered by Maddalena & Thaddeus are co mpared to the star-forming Rosette molecular cloud. The comparisons su ggest that the clumps in a cloud may be characterized as being either dormant, incipient star forming, or star forming. In the Rosette molec ular cloud, each set accounts for, respectively, 80%, 10%, and 10% of the total mass, but in G216-2.5, nearly 100% of the clumps are dormant . The physical conditions of the clumps in both clouds suggest a mass agglomeration evolutionary sequence from dormant to star-forming clump s. Detailed results for the clumps in both clouds are as follows. Clum p excitation conditions are remarkably uniform in G216-2.5 but show wi de variation in the Rosette. CO (3-2) integrated intensities and the r atio of(3-2) to (1-0) emission are significantly greater in the star-f orming cloud and greatest of all in those clumps with embedded IRAS so urces. The ratio of CO (3-2) to (1-0) line widths is also greater in t he Rosette cloud. Peak clump CO (1-0) temperatures are greater in the Rosette than G216-2.5, implying higher gas kinetic temperatures, and a re highest of all for those clumps associated with IRAS sources. The r atios of peak CO (3-2) to (1-0) temperatures, however, are comparable in the two clouds, which implies that the volume density of emitting g as in the clumps in each cloud is similar, n(H2) similar or equal to 1 0(3) cm(-3). The CS observations indicate the presence of denser gas, n(H2) similar to 10(5) cm(-3), in the clumps in each cloud. CS integra ted intensities are generally an order of magnitude weaker than (CO)-C -13 emission in each cloud, but the ratio of the two is a factor of 2 less in G216-2.5. CS to (CO)-C-13 line width ratios are also lower in G216-2.5, which suggests that there is a deficiency of dense gas relat ive to the Rosette. Again, the star-forming clumps in the Rosette poss ess the highest ratios. In addition, CO (2-1) emission was mapped over the central region of G216-2.5 and compared to a CO (1-0) map. The ra tio of (2-1) to (1-0) integrated intensities increases toward the clum p edges, which is opposite to the Sakamoto et al. study of the Orion m olecular cloud. High-resolution (CO)-C-13 (2-1) maps of one clump in e ach cloud are compared to (CO)-C-13 (1-0) maps for evidence of further fragmentation. The (2-1) radial profile is steeper than the (1-0) pro file in each clump but decreases at the same relative rate in the two clumps despite their different absolute sizes. We conclude that the di fferences between clouds and clumps that are forming stars are most re adily apparent in the warmer, denser gas traced by the CO (3-2) and CS (2-1) observations and note that there are two starless clumps in the Rosette molecular cloud with CO properties that are more characterist ic of the star-forming clumps than the other starless clumps: these ar e the best candidates for the sites of future star formation in the cl oud.