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We present a principal component analysis of 23 line of sight parameters (including the strengths of 16 diffuse interstellar bands, DIBs) for a well-chosen sample of single-cloud sightlines representing a broad range of environmental conditions. Our analysis indicates that the majority ($\sim$93\%) of the variations in the measurements can be captured by only four parameters The main driver (i.e., the first principal component) is the amount of DIB-producing material in the line of sight, a quantity that is extremely well traced by the equivalent width of the $\lambda$5797 DIB. The second principal component is the amount of UV radiation, which correlates well with the $\lambda$5797/$\lambda$5780 DIB strength ratio. The remaining two principal components are more difficult to interpret, but are likely related to the properties of dust in the line of sight (e.g., the gas-to-dust ratio). With our PCA results, the DIBs can then be used to estimate these line of sight parameters., Comment: 29 pages, 17 figures; accepted for publication in The Astrophysical Journal

Cosmic Fullerenes Since the discovery of the buckminsterfullerene C 60 in laboratory experiments, it has been speculated that fullerenes could form abundantly in carbon-rich evolved stars and, because of their stability, survive the harsh radiation field in the interstellar medium as a gas-phase species. Cami et al. (p. 1180 ; published online 22 July; see the Perspective by Ehrenfreund and Foing ) have detected large amounts of fullerenes in a peculiar planetary nebula with an extremely hydrogen-poor dust formation zone. Contrary to expectations, the fullerenes are not gaseous; they are cool, are in a neutral charge state, and represent about 1.5% of the available carbon.

We present a homogeneous database of synthetic molecular absorption and emission spectra from the optical to mm wavelengths for a large range of temperatures and column densities relevant for various astrophysical purposes, but in particular for the analysis, identification, and first-order analysis of molecular bands in spectroscopic observations. All spectra are calculated in the LTE limit from several molecular line lists, and are presented at various spectral resolving powers corresponding to several specific instrument simulations. The database is available online at http://www.spectrafactory.net, where users can freely browse, search, display, and download the spectra. We describe how additional model spectra can be requested for (automatic) calculation and inclusion. The database already contains over half a million model spectra for 39 molecules (96 different isotopologues) over the wavelength range 350 nm-3 mm (≈3-30000 cm–1).