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E.A. Bergin, G.J Melnick, J.R. Stauffer, M.L.N. Ashby, S.C. Kleiner, B.M. Patten, R. Plume, V. Tolls, Z. Wang, Y.F. Zhang (CfA), P.F. Goldsmith (Cornell U., NAIC), M. Harwit (Cornell U.), N.R. Erickson, J.E. Howe, R.L. Snell (UMass, Amherst), D.A. Neufeld (JHU), D.G. Koch (NASA ARC), R. Schieder, G. Winnewisser (U. Köln), G. Chin (NASA GSFC)
A long standing prediction of current theory has been that water and molecular oxygen are important reservoirs of elemental oxygen in the interstellar medium and, as a consequence, major coolants of the molecular gas as it collapses to form stars and planets. The analysis of SWAS observations has set sensitive upper limits on the abundance of O2 and has provided H2O abundances toward a variety of star forming regions. Based on these results, we show that H2O and O2 are not primary carriers of elemental oxygen in extended molecular clouds. Instead the available oxygen -- which may or may not be the solar oxygen abundance -- is presumably frozen on dust grains in the form of molecular ices, with a significant portion potentially remaining in atomic form, along with CO, in the gas phase. Given the low abundances for H2O and O2 in extended quiescent molecular gas, they are not significant coolants. In the case of H2O, a number of known chemical processes can locally elevate its abundance in regions with enhanced temperatures, such as warm regions surrounding young stars or in hot shocked gas. Thus, locally water can be an important, if not dominant, coolant. The new information provided by SWAS, when combined with recent results from the Infrared Space Observatory, also provide several hard observational constraints for theoretical models of the chemistry in molecular clouds and we will discuss the various models that satisfy these conditions.
The SWAS Team gratefully acknowledges NASA contract NAS5-30702
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