OBSERVATIONAL PROJECTS - BERKELEY

Diffuse Interstellar Bands

       In recent years, I have become actively involved in the study of the diffuse interstellar bands (DIBs), a series of unidentified absorption lines seen in the spectra of nearly all reddened stars, and thought to be due to large gas-phase molecules. In collaboration with Lew Hobbs, Dan Welty, Julie Thorburn, Takeshi Oka, and Don York at the University of Chicago, Brian Rachford and Ted Snow at CU Boulder, Paule Sonnentrucker at Johns Hopkins, and Scott Friedman at STScI, we have just completed a long-term survey of the DIBs using the echelle spectrograph on the 3.5-meter telescope at the Apache Point Obseratory. The goal of this survey has been to obtain high signal-to-noise spectra of a large sample of reddened stars (with complete spectral coverage from 3600 to 10200 Angstroms) as well as unreddened comparsion stars.

       Now that the observing is complete (119 half-nights!), a complete analysis of the dataset has begun. However, preliminary studies on partially complete subsets of the data have already yielded many interesting results. For example, we have identified a set of DIBs whose strengths correlate with the column density of C₂ -- this is the first time any of the DIBs have been shown to correlate with a known species! Additionally, we have been able to use our high quality spectra to rule out two proposed DIB carriers (C₇^- and l-C₃H₂^-). A detailed study of the correlations among the DIBs is underway, as is the preparation of a new DIB atlas.

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