W49A North - Global, Local, or no Collapse?
Abstract
Radiative transfer calculations have been performed in an attempt to fit profiles of several CS transitions (J=2-1 3-2 5-4 7-6) observed towards HII regions A B G in the star-forming complex W49A North. Three models were considered: global collapse of a very large (5 pc radius) cloud localized collapse of smaller (1 pc) clouds and multiple static clouds. For all three models it was possible to find combinations of parameters that reproduce the CS profiles reasonably well provided that the component clouds have a core/ envelope structure with a temperature gradient. Cores with high temperature and high molecular hydrogen density are needed to match the higher transitions (e.g. J=7-6 with 20"" beam). The low density gas needed to create the inverse P-Cygni profile seen in the CS J=2-1 line (with 5"" beam) towards HII G arises from different components in the 3 models. The infalling envelop of G plus cloud B creates the absorption in global collapse cloud B is responsible in local collapse and a separate cloud G' is needed in the case of many static clouds.
Research partially supported by the National Science Foundation USA; grants AST90-24503 93-20239 and 96-13999 to the University of Illinois- Publication:
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IAU Symposium
- Pub Date:
- 2003
- Bibcode:
- 2003IAUS..221P..32D