Modeling gas-phase H₂O between 5 $\mathsf{\mu}$m and 540 $\mathsf{\mu}$m toward massive protostars

Abstract

Abstract. We present models and observations of gas-phase H 2 O 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 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 2 O lines for 4 sources to probe the chemical structure of these massive protostars. The results indicate that pure gas-phase production of H 2 O 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 ∼ 90-110 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 2 O 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 2 O lines, however, in contrast with the case for Orion. The results show that three of the observed and modeled H 2 O lines, the 3 03 −2 12 , 2 12 −1 01 , and 1 10 −1 01 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.

Water abundances in high-mass protostellar envelopes:Herschelobservations with HIFI

“…Our observed spread in abundances of a factor of ∼100 is much greater than this uncertainty. The same range of abundances is found in other HIFI-based studies of high-mass star-forming regions (van der Tak et al 2010;Chavarría et al 2010), and also in previous work with ISO (Boonman et al 2003) and from the ground (van der Tak et al 2006). …”

Water in massive star-forming regions: HIFI observations of W3 IRS5

“…2). Boonman et al (2003) observed the outflow in W3 IRS5 in CO J = 7−6 with the JCMT and found a similar line width to what is in the water broad component. We assume that the broad component is due to the outflow.…”

The chemistry of high-mass star formation

“…Furthermore, rotational lines have a much higher sensitivity (down to abundances of ∼10 −12 ) than ro-vibrational lines. Clearly, the infrared and (sub-)millimeter techniques are complementary, and both are needed for a complete picture of the chemistry in star-forming regions (e.g., Boonman et al 2003). …”

“…Third, H 2 O remains undetected in several classes of objects, notably low-mass star-forming cores. Finally, the link between the high H 2 O abundances on small scales and the low values on large scales is still poorly understood (e.g., Boonman et al 2003). The HIFI spectrometer and PACS camera onboard the Herschel space observatory will allow key progress on these questions.…”