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Aims: Spectrally resolved circumstellar H2O(1_10 - 1_01) lines have beenobtained towards three M-type AGB stars using the Odin satellite. This providesadditional strong constrains on the properties of circumstellar H2O and thecircumstellar envelope. Methods: ISO and Odin satellite H2O line data are usedas constraints for radiative transfer models. Special consideration is taken tothe spectrally resolved Odin line profiles, and the effect of excitation to thefirst excited vibrational states of the stretching modes (nu1=1 and nu3=1) onthe derived abundances is estimated. A non-local, radiative transfer code basedon the ALI formalism is used. Results: The H2O abundance estimates are inagreement with previous estimates. The inclusion of the Odin data sets strongerconstraints on the size of the H2O envelope. The H2O(1_10 - 1_01) line profilesrequire a significant reduction in expansion velocity compared to the terminalgas expansion velocity determined in models of CO radio line emission,indicating that the H2O emission lines probe a region where the wind is stillbeing accelerated. Including the nu3=1 state significantly lowers the estimatedabundances for the low-mass-loss-rate objects. This shows the importance ofdetailed modelling, in particular the details of the infrared spectrum in therange 3 to 6 micron, to estimate accurate circumstellar H2O abundances.Conclusions: Spectrally resolved circumstellar H2O emission lines are importantprobes of the physics and chemistry in the inner regions of circumstellarenvelopes around asymptotic giant branch stars. Predictions for H2O emissionlines in the spectral range of the upcoming Herschel/HIFI mission indicate thatthese observations will be very important in this context.

Circumstellar water vapour in M-type AGB stars: Constraints from H2O(1_10 - 1_01) lines obtained with Odin