DIFFUSE INTERSTELLAR BANDS CORRELATED WITH CARBON MOLECULES $C_{2}$ and $C_{3}$
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Date
2003
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Publisher
Ohio State University
Abstract
Our survey of diffuse interstellar bands (DIBs) toward 53 stars with color excesses $0.11 \leq E(B-V) \leq 1.99$ has revealed ``the $C_{2}$ DIBs'', a class of about a dozen weak and narrow DIBs whose intensities correlate well with column densities of carbon molecules $C_{2}$ and $C_{3}$ with the correlation coefficient $r = 0.85 {\sim} 0.50^{a}$. They are strongest toward HD 204827, the star whose sightline contains by far the highest $C_{2}$ and $C_{3}$ column $densities,^{b}$ and weak or undetectable toward Herbig's classic DIB star HD 183143, although the two stars have comparable color excess of 1.11 and 1.27, respectively. The $C_{2}$ DIBs have high correlation among them $(r = 0.94 {\sim} 0.54$, mostly $\geq 0.75$) suggesting that their carriers are several molecules with similar chemical properties that exist abundantly in the diffuse interstellar medium where carbon molecules abound. We note among the $C_{2}$ DIBs 4 pairs of doublet lines with very close spacings of $20.9 {\sim} 19.1 cm^{-1}$. High correlations between the components of a doublet suggest that they are due to the same molecule. The magnitude of the splitting and the relative intensities of the doublets of $4 {\sim} 2$ suggest that they are spin-orbit split levels of linear molecules.
Description
$^{a}$J. A. Thorburn, L. M. Hobbs, B. J. McCall, T. Oka, D. E. Welty, S. D. Friedman, T. P. Snow, P. Sonnentrucker and D. G. York, ApJ 584, 339 (2003) $^{b}$T. Oka, J. A. Thorburn, B. J. McCall, S. D. Friedman, L. M. Hobbs, P. Sonnentrucker, D. E. Welty, and D. G. York, ApJ 582, 823 (2003)
Author Institution: Department of Astronomy \& Astrophysics, the University of Chicago; Department of Astronomy, University of California at Berkeley; Department of Astronomy, Space Telescope Science Institute;; Department of Astronomy, University of Colorado
Author Institution: Department of Astronomy \& Astrophysics, the University of Chicago; Department of Astronomy, University of California at Berkeley; Department of Astronomy, Space Telescope Science Institute;; Department of Astronomy, University of Colorado