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 language | English |
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Pages (from-to) | 1299-1313 |
Number of pages | 15 |
Journal | Monthly Notices of the Royal Astronomical Society |
Volume | 445 |
DOIs | |
Publication status | Published - Dec-2014 |
Keywords
- astrochemistry
- ISM: abundances
- ISM: individual objects: G34.26+0.15
- ISM: molecules