Collaborative Research: Carriers, Charge State and Diagnostic Use of the Long-Mysterious Diffuse Interstellar Bands

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This work investigates which atoms, ions, small and large molecules cause certain interstellar absorption features known as "Diffuse Interstellar Bands" (DIBs). About 600 absorption lines associated with these families of interstellar bands are known since the 1920s but their association which specific molecules is still unknown. Here researchers with different expertise in atomic and molecular spectroscopy, interstellar gas and dust, and laboratory chemistry, come together to tackle this long-standing open question. The approach is to compile and organize existing observations in databases and to add new measurements of DIBs seen toward about 220 stars to assess and to search for empirical relations between the different DIB absorption features as well as other interstellar parameters such as density and ionization state. The existing list of DIBs of all spectral widths to uniform limit is expanded with new observations to include broad and narrow lines that only appear under certain physical conditions. For this purpose, a new atlas of stars illuminating such interstellar regions will be assembled. Another goal is to observe certain diffuse interstellar clouds to obtain the types and absorption strengths of DIBs as a function of increasing density and ionization state, which relates to the spatial distribution of particular compounds and on-going reactions within the cloud. The team members have guaranteed access to observing facilities (e.g., Apache Point Observatory) to do this part of work.As long as the types of compounds (molecules with more than 15 atoms are suspected) responsible for the DIB absorptions remain elusive, it is not possible to fully account for the chemical inventory and processes of the interstellar medium. The identification of the carriers of the DIBs will be a major step forward in understanding the chemical inventory in molecular clouds from which stars and planets form.The interdisciplinary nature of this collaborative project is very strong. It provides undergraduate- and graduate students with opportunities to work on problems related to more than one discipline.