Understanding water deuterium fractionation is important for constraining the mechanisms of water formation in interstellar clouds. Observations of HDO and H 18 2 O transitions were carried out towards the high-mass star-forming region G34.26+0.15 with the HIFI instrument onboard the Herschel Space Observatory, as well as with ground-based single-dish telescopes. Ten HDO lines and three H 18 2 O lines covering a broad range of upper energy levels (22-204 K) were detected. We used a non-LTE 1D analysis to determine the HDO/H 2 O ratio as a function of radius in the envelope. Models with different water abundance distributions were considered in order to reproduce the observed line profiles. The HDO/H 2 O ratio is found to be lower in the hot core (∼3.5 × 10 −4 -7.5 × 10 −4 ) than in the colder envelope (∼1.0 × 10 −3 -2.2 × 10 −3 ). This is the first time that a radial variation of the HDO/H 2 O ratio has been found to occur in a high-mass source. The chemical evolution of this source was modeled as a function of its radius and the observations are relatively well reproduced. The comparison between the chemical model and the observations leads to an age of ∼10 5 years after the infrared dark cloud stage.
Aims. We present observations of twelve rotational transitions of H . We analyze these observations to obtain insights into physical processes in this region. Methods. We identify three main gas components (hot core, cold foreground, and outflow) in NGC 6334 I and derive the physical conditions in these components. Results. The hot core, identified by the emission in highly excited lines, shows a high excitation temperature of ∼200 K, whereas water in the foreground component is predominantly in the ortho-and para-ground states. The abundance of water varies between 4 × 10 −5 (outflow) and 10 −8(cold foreground gas). This variation is most likely due to the freeze-out of water molecules onto dust grains. The H 18 2 O/H 17 2 O abundance ratio is 3.2, which is consistent with the 18 O/ 17 O ratio determined from CO isotopologues. The ortho/para ratio in water appears to be relatively low (1.6 ± 1) in the cold, quiescent gas, but close to the equilibrium value of three in the warmer outflow material (2.5 ± 0.8).
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