We have studied the gas and dust properties and the star forming activity in G216-2.5 (also called Maddalena's cloud), a cold, massive GMC that has no evidence for star formation. We have mapped 11 square degrees in the J = 1-0 transitions of $\sp{12}$CO and $\sp{13}$CO using the QUARRY fifteen-beam array receiver on the 14 m telescope at FCRAO. We have confirmed the results of Maddalena and Thaddeus (1985) that the cloud is unusually cold and has very broad linewidths $(\Delta V\sim8$ km s$\sp{-1}).$ The visual extinction to $\sp{13}$CO column density ratio is found to be similar to that in local molecular clouds, suggesting that if the gas to dust ratio is normal, the $\sp{13}$CO abundance relative to molecular hydrogen in this cloud is similar to that found for clouds near the sun. The low gas and dust temperatures found for this cloud are largely due to the absence of heating by massive stars. The exceptionally low gas temperature can be explained if the cosmic-ray heating rate is reduced by a factor of two in the outer Galaxy. Low luminosity, and presumably low mass, young stars have been identified in this cloud. These young stars are found preferentially on the edge of the cloud. Clusters of T Tauri stars are found in two locations within G216-2.5. The mass of the cloud has been established by several techniques, and masses between 1 $\times$ 10$\sp5$ and 6 $\times$ 10$\sp5$ $M\sb\odot$ were obtained. It is suggested that G216-2.5 is a remnant cloud from a past episode of massive star formation for the following reasons. First, the cloud has a relatively large velocity dispersion for a non-star-forming GMC. Second, there is clear evidence for shells and rings within the cloud, which may be the fossil remains of its earlier star formation activity. Third, the kinematics of the cloud is dominated by a global velocity gradient suggesting that the cloud is part of a very large expanding shell. Lastly, the discrepancy between the LTE and virial masses may be explained if the cloud has been severely perturbed and is currently expanding. G216-2.5 may be part of a larger star forming complex that includes the adjacent H scII region S287 and its molecular cloud.
| Identifer | oai:union.ndltd.org:UMASS/oai:scholarworks.umass.edu:dissertations-8293 |
| Date | 01 January 1992 |
| Creators | Lee, Youngung |
| Publisher | ScholarWorks@UMass Amherst |
| Source Sets | University of Massachusetts, Amherst |
| Language | English |
| Detected Language | English |
| Type | text |
| Source | Doctoral Dissertations Available from Proquest |
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