SummaryThe central scientific motivation of the Structure and Evolution of the Dusty Interstellar medium (SEDI) program is to provide a full picture of the dust evolution in the Interstellar Medium (ISM), from just after dust formation in stellar outflows until incorporation into the dense regions of proto-stellar cores. The proposed observations will identify the processes regulating dust evolution and indicate where and on what size scales they are active. The SEDI database, in combination with follow-up observations on SIRTF, ground-based and airborne observatories, and future space projects will constitute a lasting reference to investigate the nature of interstellar dust and the interplay between its composition and the physical, chemical and dynamical properties of the ISM. Finally, the point SEDI Point Source Catalog will be a goldmine for studies of many types and in particular for star formation research. We propose to map fifty square degrees of the sky with all seven SIRTF photometric bands from 3.6 to 160 micron distributed over 16 fields covering the diversity of environments penetrated by starlight. The total amount of observing time of this proposal is 646 hours. The fields will target dust in the warm and cold atomic ISM and molecular gas residing outside of dark cores. It is within this diffuse medium that most of the interstellar matter resides and which needs to be observed to follow dust evolution in interstellar space. Second look spectroscopic observations with IRS and the SED mode of MIPS, on positions selected from the SIRTF images, will complement the mapping data by providing template spectra of dust emission for the full range of observed spectral energy distribution (SED). The dust SED and emission spectra will allow us to study the physical processes acting on dust through the impact of these processes on the size distribution of the grains and their emission properties. The SIRTF observations will be complemented by ground based ancillary data: CO, HI and optical observations which will permit an analysis of the dust properties in relation to the ISM structure. In addition, modeling of the dust emission and of physical processes acting on dust is an essential part of our proposal. This SIRTF Legacy Program gathers a dedicated and committed team of researchers with wide-ranging experience in all observational and theoretical areas of research and data processing relevant to this project. Our team is comprised of astronomers who have worked on past infrared space mission data (e.g., IRAS, COBE and ISO) and who have proven competence in producing the best possible images of, and source catalogs for, the diffuse ISM at infrared wavelengths, e.g., most recently from observations obtained with ISO. We will develop new tools, including models for the response of the SIRTF detectors, which will stimulate more general use of the SIRTF imaging and spectroscopic capabilities for faint extended emission. The SEDI team includes members who will contribute to the ground based ancillary observations which will be essential to the interpretation of the information provided in the SEDI SIRTF data base. The data reduction and the construction of the data base will be executed in a timely manner and will deliver preliminary versions of the images and a catalog for SIRTF follow-up observations within this SEDI Legacy Program to benefit the entire astronomical community.
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