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==> This proposal requests an upgrade from Priority 3 for JPUGET.PUGET_1
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We propose to do a spectral exploration of the cold interstellar matter
in the wavelength range accessible to ISO. The excellent sensitivity
of ISO makes it unique to detect spectral features in low brightness extended
sources. Spectra of the integrated galactic emission will be obtained on lines
of sight with high column density of interstellar gas avoiding regions of
massive star formation. The large column density, combined with long
integration times, will provide a high signal to noise on the continuum
and allow the detection of weak dust features, vibration modes of individual
PAHs molecules, molecular emission from hot spots in HI clouds possibly
heated by intermittent dissipation of turbulence, vibrational transitions
of molecules seen in absorption against the diffuse emission of PAHs and
very small grains, and the associated emission.
This proposal is a follow up of the proposal PUGET_1 which was partially
supported in the first call. The time allocated in priority 2 allowed only the
SWS spectrum to be done on one line of sight. The LWS grating observations are
covered in the "galactic line of sight" central program. The first results from
these observations confirm the existence of high excitation lines in this cold
medium. We request an upgrade of the priority 3 time for the second line of
sight and SWS and LWS Fabry-Perot observations.