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

The following document lists the file abstract/ECAUX_OI_ABS.abs from catalogue VI/111.
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Oxygen is the third most abundant element in the universe. In the gas phase
of the interstellar medium, oxygen is believed to be found principally in the
species such as O, O2, CO, OH and H2O. From the present observations of the ISM
it seems that none of these molecules could account for the bulk of the gas-
phase oxygen. What is the major depository of the gas-phase oxygen in the cold
component of the ISM is still one of the outstanding open question in
interstellar chemistry.
Recent observations from KAO and more unambiguously from ISO showed the evidence
of OI 63um absorption in galactic molecular clouds - HII region complexes. This
important result shows that a considerable column density of atomic oxygen is
present along the line of sight of such complexes. Observations with ISO LWS
grating (unresolved lines) of ultra compact HII regions, as well as of high
mass Pre-Main sequence objects, show a ratio of the OI (63um) to OI (145um)
which can be explain only if a strong absorption of the OI 63um is present.
Furthermore, LWS FPs observations of the OI broad emission line from the galaxy
M82 have been performed. The line is clearly resolved by the LWS FP and exhibit
a strong feature in absorption, likely unresolved, at the rest wavelength of the
OI line. This result would indicate that absorption by atomic oxygen should be
mainly due to diffuse galactic clouds along the line of sight to M82.
This proposal intends to study the actual distribution of atomic oxygen, in
its ground state, from the OI line seen in absorption against a selection of
bright sources in the galactic plane and a few at higher galactic latitudes.
The main goal is to derive the quantity of oxygen in its atomic form within
the galactic ISM. The sources have been chosen also to be at a range of
galactocentric radius to study a possible variation of the OI absorption at
large scale in the Galaxy. Several sources of each type (giant molecular cloud -
HII region complexes, Pre-main sequence star and ultra compact HII regions) are
requested to be observed to check the possibility for some of these to present
an OI absorption coming from cold material associated with their surroundings,
rather than from the diffuse medium on the line of sight.

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