The following document lists the file abstract/SDRAPATZ_MPEWARM2.abs
from catalogue VI/111.
A plain copy of the file
(without headers/trailers) may be downloaded.
SCIENTIFIC ABSTRACT
The warm (100 - 5000 K), dense (n(H_2) > 10^3 cm^-3) interstellar
medium is a decisive component of the whole interstellar medium and is
closely coupled to key processes like star formation and evolution. It
is heated through a wide variety of astrophysically important processes
such as shocks of various types, X-ray irradiation, UV irradiation of
interface regions near HII regions, and stellar radiation in the environment
of young objects. A rich variety of lines in the IR and submm wavelength
region will provide a unique opportunity to investigate the physics,
chemistry and interrelation of corresponding phenomena by multi-line
spectroscopy of various molecules, atoms and ions. However, since allmost
all lines cannot be observed from ground based telescopes or even from an
airborne observatory (KAO) ISO would offer the first and only possibility
for this investigation.
We have selected four classes of objects each representing different
processes that heat the gas: (1.) photon-dominated regions at the
interfaces of HII regions (including reflection nebulae), (2.) shocks of
various types: strong shocks (J-type) in supernova remnants and moderate
or weak shocks (also C-type) in outflow sources, (3.) embedded sources
(star formation) where dust is radiatively heated by the central source
and gas is heated by dust, and (4.) regions of X-ray excitation.
For each class a small number of prototypical, bright sources and a
set of spectral lines in the ISO wavelength range has been selected.
The set of radiative transitions is selected thus that a maximum of
information can be gained for each individual class of objects.
Much emphasis is placed on the observation of (faint) important lines
rather than on mapping because of time constraints by the faintness of some of
the crucial lines. Using these sources as a kind of templates we also establish
a set of crucial lines with which different processes can be distinguished.
The primary target lines for all four classes are the rotational
transitions of H_2 in order to study directly the bulk of the warm gas.
Through observation of rotational transitions in oxygen-bearing
species such as OH, H_2O, and H_2^{18}O, and O_2, the oxygen
chemistry in interstellar clouds will be studied for the first time via direct
determination of all important reactants rather than by default.
Most of these molecules serve also as a major coolant and therefore their
abundances have a great impact on the energy balance of the warm molecular gas.
This balance is also determined by the cooling of fine-structure lines
where their contribution will be studied through a set of diagnostically
useful transitions.
We also propose the observation of a few selected rovibrational transitions
in molecular ions that become quite abundant in objects where the gas is excited
through X-ray irradiation. This unique possibility will enable us to get a
handle on that process. In a few objects where the gas is cold (T < 30 K)
absorption measurements will be performed. The study of the lowest
rotational transitions of H_2 and HD will provide a first and accurate
determination of their total column density in this general environment.
These observations are closely related to the emission measurements mentioned
above. Furthermore, a series of transitions in the first fundamental band
of H_2O, H_2^{18}O, CH_4, and CO_2 will be observed. Since a detailed
scientific proposal would by far exceed the granted space we include a list of
lines for each class of objects in the scientific justification.
OBSERVATION SUMMARY
We plan to take advantage of the spectroscopic capabilities of ISO over its
full wavelength range, using the following AOTs:
SWS: Medium and high resolution spectroscopy with the AOTs SWS01,SWS02,
SWS06,SWS07
LWS: Medium resolution full grating scans and high resolution line scans
with AOTs LWS01,LWS04
A detailed description of our observing strategy and outline of integration
times exceeds the limits of this abstract.