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.
Instrument
LWS01 , LWS04 , SWS01 , SWS02 , SWS07
Temporal Coverage
1996-02-05T10:24:31Z/1998-04-10T11:50:05Z
Version
1.0
Mission Description
The Infrared Space Observatory (ISO) was the worlds first true orbiting infrared observatory. Equipped with four highly-sophisticated and versatile scientific instruments, it was launched by Ariane in November 1995 and provided astronomers world-wide with a facility of unprecedented sensitivity and capabilities for a detailed exploration of the Universe at infrared wavelengths.
European Space Agency, Drapatz et al., 1999, 'Physical and Chemical Conditions in Dense comma Warm Instellar Gas comma Part 1 of 2 ', 1.0, European Space Agency, https://doi.org/10.5270/esa-sjvu6r5
