2002A&A...395..657B

We present a detailed comparison of SWAS and ISO observations of H₂O emission in a sample of outflows. By taking into consideration the different methods used to derive the fractional water abundance, we find that, despite the initial apparent discrepancies, there is satisfactory agreement between ISO and SWAS results for the outflows observed by both satellites. Such an agreement is reached by assuming that most of the detected water comes from a single region smaller than both the ISO and SWAS beam apertures and considering temperatures higher (T>100K) and density lower (n(H₂)<2x10⁶cm^–3) than previously adopted. The ratio between the integrated flux of the ortho-H₂O 2₁₂-1₀₁ line at 179.5µm observed by ISO and the fundamental ortho-H₂O 1₁₀-1₀₁ line at 538.3µm observed by SWAS is always smaller (never by more than a factor of 7) than the expected ratio. We propose that the fundamental ortho-H₂O transition has a contribution from a cooler gas component to which SWAS is sensitive but which is not traced by ISO. We conclude that, while ISO and SWAS observations are consistent with chemical models predicting a significant enhancement of water vapor abundance in outflow regions, the explanation for the low water abundance derived from SWAS observations of the cold ISM is still unclear.