: |
: |
|---|
T. OKA, J. A. THORBURN, L. M. HOBBS, D. E. WELTY, D. G. YORK, Department of Astronomy & Astrophysics, The University of Chicago, Chicago, IL 60637; B. J. MCCALL, Department of Astronomy, University of California, Berkeley, CA 94720; S. D. FRIEDMAN AND P. SONNENTRUCKER, Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218.
\hspace0.3in Following the detection of the 000-000 band of the A1
u
X1
g+ transition of C3 at 4051.6~Å by Maier and others toward three diffuse sightlines, we have searched for the spectrum toward more reddened stars. Although the lower resolution (R = 37,500) of our spectrometer (ARCES) did not resolve the rotational structure of the spectrum, it allowed us to observe denser clouds toward fainter stars which are expected to contain more carbon molecules. The C3 spectrum has been observed toward 15 stars with color excesses ranging from E(B-V) = 0.33 to 1.12 and the C3 column densities were determined by comparing the observed spectra with simulated spectra. The observed C3 column densities from 1012 to 1013 cm-2 are well correlated with the C2 column densities indicating their close chemical relation. The formation of C3 from C2 will be discussed. The studies of C3 and C2 have led us to the revelation of a group of diffuse interstellar bands whose intensities correlate well with the C3/C2 column densities. It was also noted that abundances of C3/C2 and H3+ are completely uncorrelated.
.1in\hspace0.3in Our non-detection of the 020-000 vibronic band at 3991.6~Å set an upper limit to its Franck-Condon factor and that of C4 and C5 set upper limits of their column densities.
.3in