Publikationsdatum:
2014-10-12
Beschreibung:
Understanding water deuterium fractionation is important for constraining the mechanisms of water formation in interstellar clouds. Observations of HDO and H $_2^{18}$ O transitions were carried out towards the high-mass star-forming region G34.26+0.15 with the Heterodyne Instrument for the Far-Infrared (HIFI) instrument onboard the Herschel Space Observatory , as well as with ground-based single-dish telescopes. 10 HDO lines and three H $_2^{18}$ O lines covering a broad range of upper energy levels (22–204 K) were detected. We used a non-local thermal equilibrium 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 modelled 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 yr after the infrared dark cloud stage.
Print ISSN:
0035-8711
Digitale ISSN:
1365-2966
Thema:
Physik
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