Water deuterium fractionation in the high-mass star-forming region G34.26+0.15 based on Herschel/HIFI data

A. Coutens, C. Vastel, U. Hincelin, E. Herbst, D. C. Lis, L. Chavarría, M. Gérin, F. F. S. van der Tak, C. M. Persson, P. F. Goldsmith, E. Caux

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Abstract

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/H2O 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/H2O 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/H2O 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 ˜105 yr after the infrared dark cloud stage.
Original languageEnglish
Pages (from-to)1299-1313
Number of pages15
JournalMonthly Notices of the Royal Astronomical Society
Volume445
DOIs
Publication statusPublished - Dec-2014

Keywords

  • astrochemistry
  • ISM: abundances
  • ISM: individual objects: G34.26+0.15
  • ISM: molecules

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