The following document lists the file abstract/ECAUX_ISM_IIB.abs
from catalogue VI/111.
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SCIENTIFIC ABSTRACT This proposal sets out a plan for observation of the diffuse infrared emission spectrum. It concerns both the Zodiacal light emission and the diffuse Galactic emission. These observations have two goals: 1/ to model the diffuse emission elsewhere in the sky to substract it from the source's emission. 2/ to get information about the chemical and physical properties of the dust grains embedded in this diffuse medium and about the thermal balance into the Galaxy, as well as the spatial variation of these properties (with the height above the plane, and with the galactocentric distance). One can define three components of the Galactic diffuse medium : the Cirrus, the HI envelopes of the Giant Molecular Clouds, and the intercloud medium that is mainly composed of HI gas outside well defined HI clouds. The study of the two first components concerns other proposals. This proposal only deals with the last component, the intercloud medium. Another fold of this proposal is the measure of the Zodiacal light spectrum and its variation with Solar elongation and Ecliptic latitude. ISOCAM images, using filters LW 1, 2 and 3, will be taken and will improve the modeling of the sky around the source, providing information on the contribution of discrete sources. OBSERVATION SUMMARY Because the infrared diffuse emission is made of several components (Zodiacal, Galactic and may be Extragalactic), to get the spectrum of the diffuse Galactic component, we will need first a good knowledge of the zodiacal light spectrum, and its variation with ecliptic latitude and Solar elongation. In a first step, we will neglect the maybe existing Extragalactic component. To get only the emission of the diffuse medium, careful analysis of IRAS maps has been made in one hand to find the best lines of sight for these observations, outside emission related to cirrus, molecular clouds as well as HI clouds. For the Zodiacal light study, we propose to observe a set of lines of sight with ISO/LWS to model the intensities and spectral variation of this component. For the Galactic Diffuse emission, we propose to get first the spectrum of the local diffuse medium at a few galactic latitude fields, where Galactic emission related to well-known HI or molecular clouds is minimal. Then, to study the variation of the diffuse emission spectrum with the galactocentric radius R, and also with the height above the Galactic plane z, we propose to get full grating scans for different latitude fields at a few set of Galactic longitudes, outside well known strong sources in or near the Galactic disc and well known nearby high latitude molecular clouds.