Modeling gas-phase H₂O between 5 m and 540 m toward massive protostars^*

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

Corresponding author: A. M. S. Boonman, boonman@strw.leidenuniv.nl

Received: 10 March 2003
Accepted: 16 May 2003

Abstract

We present models and observations of gas-phase H₂O lines between 5 and 540 μm 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 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 –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 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 , and 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.