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.
NSF Project – Final report AST 1009929 Theodore P. Snow Introduction This explores properties of the diffuse interstellar bands (DIBs), which because very important as they represent largest the reservoir of organic material in the galaxy because they contain carbon as a main ingredient. We know many aspects of the DIBs, but we haven’t identified yet. Our program, now having more 200 stars in its database, explores the number in different sightlines, the profiles under varying conditions, and the DIBs and the correlations among them, all aimed at identifying the molecules that form DIBs. Do to this research, we have observations at the Apache Point Observatory, with more that ten runs at there. I have a NASA grant lab program aimed at finding the best candidates for the DIBs by their reaction rates – the more higher the rate, the more abundant the molecule. Accomplishments Our group has published, in the three years of the grant, five major papers that I co-authored (and three others), listed here, that refined the search,; and several talks at conferences, culminating in the IAU 297: Diffuse Interstellar Bands conference in May of this year where we had three invited speakers (Snow, Sonnentrucker, Welty) talks and several contributed talks and posters. Papers published Dahlstrom, J. et al. 2013 Anomalous Diffuse Interstellar Bands in the Spectrum of Herschel 36. I. Observations of Rotationally Excited CH and CH+ Absorption and Strong, Extended Redward Wings on Several DIBs, ApJ 773, 41 Freidman, S. 2011 Studies of Diffuse Interstellar Bands V. Pairwise Correlations of Eight Strong DIBs and Neutral Hydrogen, Molecular Hydrogen, and Color Excess, ApJ 727, 33 McCall, B. 2010 Studies of the Diffuse Interstellar Bands. IV. The Nearly Perfect Correlation Between λλ6196.0 and 6613.6, ApJ 708, 162 O’Malia, K. 2012 The Search for the Diffuse Interstellar Bands and Other Molecules in Comets 17P (Holmes) and C/2007 W1 (Boattini), ApJ 708, 162 Hobbs et al. 2009 Studies of the Diffuse Interstellar Bands. III. HD 183143, ApJ 705, 32 Opportunities for training and professional development: One graduate student and three under students have contributed have been involved. Results disseminated to communities of interest: The fact that DIBs contain most of the organic material in the galaxy should be more well-known that it is. I have about is my talks and in conversation. Products See above. Persons involved Don York (U. Chicago) Lew Hobbs (U. Chicago) Julie Dalhstrom (Carthage College) Dan Welty (U. Chicago) Ben McCall (U. Illinois) Scott Friedman (Space telescope Institute Paule Sonnentrucker
