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

The following document lists the file abstract/PCOX_ISM_IA.abs from catalogue VI/111.
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SCIENTIFIC ABSTRACT
The ISO/LWS opens a unique window on molecular, atomic and ionic lines (as well
as dust bands) in molecular cloud/HII region complexes, in a spectral range
which is still essentially unexplored. The wavelength coverage of the LWS
(45 - 196 um) enables to measure in the same observing conditions transitions
of various species associated with the different phases present in the dense
parts of the interstellar medium (molecular, atomic, ionic) making the study of
relative intensities possible and, hence, the study of the chemical and
physical conditions in a coherent way. The most important cooling lines of the
warm molecular gas ([CII], [OI]) will be accessible together with transitions
of O and C bearing molecules such as OH, the high transitions of CO and for the
first time through some of the fundamental transitions of water.

The main goal of this proposal is to improve our knowledge on both the physical
and chemical conditions pertaining in galactic molecular cloud/HII region
complexes. It is proposed to use the ISO/LWS to study the dense - n>10(3)cm-3 -
parts of the interstellar gas. When present, the ultraviolet radiation of nearby
(young) stars permeates the neutral gas with photons less energetical than 13.6
eV leading to photodissociation and heating of the molecular/atomic gas. The
cooling of this gas is then dominated by a variety of strong atomic and
molecular far-infrared lines. The frequent presence of shocks is another heating
source for the gas with subsequent cooling via far-infrared lines.

OBSERVATION SUMMARY
In order to study in detail the physics and chemistry of this dense, warm
neutral gas, we selected a number of prominent nearby molecular clouds in our
Galaxy and the Magellanic Clouds spanning the range from high to low mass star
formation, one quiescent molecular cloud, one Supernova Remnant and a few
reflection nebulae. Full LWS grating spectra will be acquired for these regions
along carefully selected directions probing the various physical/chemical
conditions of the atomic/molecular phases.

In addition, we selected strong point-like infrared sources where we intend to
carry out high spectral resolution observations of some atomic and molecular
lines both in emission (compact HII regions) and in absorption (embedded young
stellar objects). These observations are proposed to analyze in greater detail
the low lying transitions of H2O and other important molecules only accessible
in the LWS wavelength range (O2, HD, HDO, OD) and address some fundamental
problems related to the influence of on-going star formation on the
neighbouring neutral gas.

Systematically a full LWS grating spectrum at each position so that, if
present, the broad features due to dust particles will be observed. The results
of the present observations together with some other LWS proposals (evolved
stars and PNe) could be combined to create a ISO LWS database on dust
properties. Such a data base, even for a small number of typical sources, is a
prerequisite for a further understanding of the chemical composition of
interstellar dust.



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