2003A&A...406..937B

We present models and observations of gas-phase H₂O lines between 5 and 540µm toward deeply embedded massive protostars, involving both pure rotational and ro-vibrational transitions. The data have been obtained for 6 sources with both the Short and Long Wavelength Spectrometers (SWS and LWS) on board the Infrared Space Observatory (ISO) and with the Submillimeter Wave Astronomy Satellite (SWAS). For comparison, CO J=7-6 spectra have been observed with the MPIfR/SRON 800 GHz heterodyne spectrometer at the James Clerk Maxwell Telescope (JCMT). A radiative transfer model in combination with different physical/chemical scenarios has been used to model these H₂O lines for 4 sources to probe the chemical structure of these massive protostars. The results indicate that pure gas-phase production of H₂O cannot explain the observed spectra. Ice evaporation in the warm inner envelope and freeze-out in the cold outer part are important for most of our sources and occur at T∼90-110K. The ISO-SWS data are particularly sensitive to ice evaporation in the inner part whereas the ISO-LWS data are good diagnostics of freeze-out in the outer region. The modeling suggests that the 557-GHz SWAS line includes contributions from both the cold and the warm H₂O gas. The SWAS line profiles indicate that for some of the sources a fraction of up to 50% of the total flux may originate in the outflow. Shocks do not seem to contribute significantly to the observed emission in other H₂O lines, however, in contrast with the case for Orion. The results show that three of the observed and modeled H₂O lines, the 3₀₃-2₁₂, 2₁₂-1₀₁, and 1₁₀-1₀₁ lines, are good candidates to observe with the Herschel Space Observatory in order to further investigate the physical and chemical conditions in massive star-forming regions.