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dc.creatorMcCall, Benjamin J.en_US
dc.creatorRachford, B. L.en_US
dc.creatorSnow, T. P.en_US
dc.creatorSonnentrucker, P.en_US
dc.creatorFriedman, S. D.en_US
dc.creatorThorburn, J. A.en_US
dc.creatorOka, T.en_US
dc.creatorWelty, D. E.en_US
dc.creatorHobbs, L. M.en_US
dc.creatorYork, Donald G.en_US
dc.description$^{a}$Based on observations from the APO 3.5-meter telescope, owned and operated by the Astrophysical Research Consortium.en_US
dc.descriptionAuthor Institution: Department of Astronomy \& Department of Chemistry, University of California at Berkeley; Center for Astrophysics and Space Astronomy, University of Colorado at Boulder;; Department of Physics and Astronomy, Johns Hopkins University; Department of Astronomy \& Astrophysics, University of Chicagoen_US
dc.description.abstractWe are in the midst of a long-term survey of the diffuse interstellar bands (DIBs) using the high resolution $(R \sim 37500)$ echelle spectrograph on the 3.5-meter telescope at Apache Point Observatory (APO). Our aim is to obtain high S/N spectra of a large sample of reddened stars. Three years into this program, we have achieved S/N ratios (at 5780 {\AA}) of $> 500$ on over 100 stars and $> 1000$ on over 50 stars, with complete spectral coverage from $\sim 3600-10200 {\AA}$. One early result from this program has been the identification of a set of narrow (FWHM $0.46-0.99 {\AA}$) DIBs that appear to be stronger, relative to many broader DIBs, in sightlines with above average $C_{2}$ column densities per unit reddening. The lines of sight which show strong ``$C_{2}$ DIBs'' have been observed to contain a greater fraction of their interstellar absorption in the form of translucent clouds. Many of these DIBs appear in pairs with similar splittings of about $20 cm^{-1}$ (e.g. 4963.87 \& 4969.12, 4979.58 \& 4984.78, 5170.44 \& 5175.99), reminiscent of a spin-orbit interaction in a linear molecule. We have also begun to identify other families of DIBs that show fairly good intensity correlations from star to star, which could indicate common (or at least chemically related) carriers. Unlike the ``$C_{2}$ DIBs,'' it appears that most DIBs are prevalent in diffuse gas, where hydrogen is more atomic than molecular. In dense sightlines such as HD 62542, even the strongest DIBs are barely detectable, despite a relatively large amount of interstellar extinction. In addition, we find that the intensities of most DIBs correlate better with the column density of $H (r \succeq 0.5)$ than with that of $H_{2}$ (mostly $\preceq 0.5$). We expect that this survey will also provide a valuable resource for comparisons with laboratory spectra of potential DIB carriers. Already our data have been used to exclude $C^{-}_{7}$ and $l-C_{3}H^{-}_{2}$ as DIB carriers.en_US
dc.format.extent387096 bytes
dc.publisherOhio State Universityen_US

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