Contents of: VI/111/./abstract/JCERNICH_CERNI_1.abs

The following document lists the file abstract/JCERNICH_CERNI_1.abs from catalogue VI/111.
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  For  many  years  the  extent  of water emission and its abundance in
molecular    clouds  have  been  key  problems  in  the  study  of  the
interstellar  medium -ISM-. Although all chemical models predict a high
water  abundance,  ground-based observations of non-masering rotational
transitions  of water are practically impossible. The first detected 22
GHz  transition  of water, which has been observed in many star forming
regions,  circumstellar  envelopes  and external galaxies, is in fact a
maser  emission  which  probes  small  volumes  of gas characterized by
extreme  physical  conditions. Recently, Cernicharo et al. (1990, 1994)
succeeded   in  observing  at  183  GHz  the  weakly  masering  313-220
transition  of  water  in many molecular clouds opening a new window to
study  water in the ISM. In particular, it was shown for the first time
that  water  emission  in  Orion  is  spatially  extended.  The derived
abundances demonstrate that water is one of the most abundant molecular
species  in  warm molecular clouds. However, the masering nature of the
313-220  transition  limits  its  use  as  a diagnostic of the physical
conditions  of the gas and the excellent weather conditions required to
observe at 183 GHz clearly restricts its measurement.
  ISO  is  the  only  instrument in the next decade which will allow to
observe at high spatial resolution and sensitivity the thermal emission
of  water  vapor  in  the  ISM.  The  angular  resolution of ISO in the
far-infrared  together  with the sensitivity of the LWS FP spectrometer
will enable to map and resolve the large scale distribution of water in
nearby  molecular  clouds.  We  propose to map several nearby molecular
clouds  in  two  lines of H2O connecting low-lying energy levels. Other
transitions  of  water  and its rare HH18O isotope will be made towards
selected positions in these molecular clouds. The proposed observations
will provide fundamental data on the distribution of water in molecular
clouds  and  will  result  in  a major contribution to our knowledge of
water and its role in the interstellar medium.

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