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Session 52 - First Results from the Infrared Space Observatory.
Oral session, Wednesday, June 12
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We have observed four water vapor transitions in W Hya, using the European Space Agency's (ESA) Infrared Space Observatory (ISO) Short Wavelength Spectrometer (SWS). Three of the transitions were observed in the instrument's Fabry-Perot mode: 4(3,2)\rightarrow3(0,3) at 40.69\mum, 4(4,1)\rightarrow3(1,2) at 31.77\mum, and 7(2,5)\rightarrow6(1,6) at 29.84\mum, at a resolving power of order 30,000. One additional line, 4(4,1)\rightarrow4(1,4) at 37.98\mum, was observed in the grating mode, where the resolving power was about 2,000. The observed fluxes, respectively were 1.2, 1.1, 1.4 and 1.2 in units of 10^-19 Watt cm^-2. These fluxes are between 50-80% of the values predicted by Wesley Chen and David Neufeld, ApJ. 453, L99 (1995). The agreement is well within the uncertainties in the absolute values of the observed fluxes and in the reported measurements of mass loss on which the theoretical predictions are based. This represents the first detection of thermal water vapor emission from a circumstellar outflow, and is significant in that the Chen-Neufeld predictions are an order of magnitude lower than previous estimates. The significance of these results for modeling the formation and outflow of water vapor in stellar atmospheres will be discussed. We intend also to summarize observations obtained by other SWS observers of water vapor emission in other stars and embedded objects.
