EDP Sciences
Free access
Volume 406, Number 3, August II 2003
Page(s) 937 - 955
Section Formation, structure and evolution of stars
DOI http://dx.doi.org/10.1051/0004-6361:20030765

A&A 406, 937-955 (2003)
DOI: 10.1051/0004-6361:20030765

Modeling gas-phase H $\mathsf{_2}$O between 5  $\mathsf{\mu}$m and 540  $\mathsf{\mu}$m toward massive protostars

A. M. S. Boonman1, S. D. Doty2, E. F. van Dishoeck1, E. A. Bergin3, G. J. Melnick3, C. M. Wright1 and R. Stark4

1  Sterrewacht Leiden, PO Box 9513, 2300 RA Leiden, The Netherlands
2  Department of Physics and Astronomy, Denison University, Granville, Ohio 43023, USA
3  Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
4  Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany

(Received 10 March 2003 / Accepted 16 May 2003 )

We present models and observations of gas-phase H 2O lines between 5 and 540  $\mu$m 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 H 2O lines for 4 sources to probe the chemical structure of these massive protostars. The results indicate that pure gas-phase production of H 2O 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 $T\sim90$-110 K. 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 H 2O 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 H 2O lines, however, in contrast with the case for Orion. The results show that three of the observed and modeled H 2O 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.

Key words: ISM: abundances -- ISM: molecules -- infrared: ISM -- ISM: lines and bands -- molecular processes

Offprint request: A. M. S. Boonman, boonman@strw.leidenuniv.nl

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