| Description |
Observations of the HDO molecules are an important complement for studies of
water, since they give strong constraints on the formation processes: grain
surfaces versus gas-phase chemistry through energetic process as shocks.
HIFI observations of multiple transitions of HDO in SgrB2(M) combined with
ground-based observations allowed for the first time the determination of its
abundance throughout the envelope. In the framework of the PRISMAS Key
Program, a large sample of high-mass star-forming regions have been
observed with the detection of many species in their line of sight. The HDO
(111-000) fundamental transition has also been detected in absorption at the
velocity of the hot core towards the 2 sources that have been observed so far,
probably tracing the colder envelope in its surrounding.
We propose to observe higher energy level HDO transitions towards a sample of
three compact HII regions that will be targeted by the PRISMAS Key Program
(G34.3+0.1, W33A, W49N) in order to perform a full modeling from the hot core
through the envelope using a spherical Monte Carlo radiative transfer code,
RATRAN, which takes into account radiative pumping by continuum emission from
dust. We will use for an optimum accuracy of the modeling the HDO and D2O
collision rates with H2, recently computed within our group, that are not available
in the public so far.
This study will hopefully give strong constrains on the formation processes of
water, combining the proposed observations with published or soon to be
published high resolution H2O observations with HIFI towards the same sources. |
