Carbon Chains in the Diffuse Interstellar Medium

       A useful by-product of our DIB observations has been the detection of the C3 band at 4051 Angstroms in a set of 10 highly reddened translucent cloud sightlines. However, the resolving power of the APO echelle is not sufficient to rotationally resolve the band, so Mate Adamkovics (a chemistry graduate student at Berkeley) and I decided to follow up the APO detections using the Hamilton echelle at Lick Observatory. Those followup observations, together with some data obtained in collaboration with Geoff Blake (Caltech) at Keck Observatory, yielded 10 rotationally-resolved detections of C3. Interestingly, the column densities of C2 and C3 seem to be fairly well correlated in this sample of sightlines. Because of our high signal-to-noise ratios and resolution, we were able not only to determine accurate column densities, but also to analyze the rotational excitation of C3 in some detail. A deep search is underway (at Keck) for the spectra of the longer carbon chains C4 and C5.


M. Adamkovics, G. A. Blake, and B. J. McCall
Observations of Rotationally Resolved C3 in Translucent Sight Lines
Astrophysical Journal, 595 (Sept. 20, 2003), in press

T. Oka, J. A. Thorburn, B. J. McCall, S. D. Friedman, L. M. Hobbs, P. Sonnentrucker, D. E. Welty, and D. G. York
Observations of C3 in Translucent Sightlines
Astrophysical Journal, 582, 823 (2003)