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2003ApJ...584..339T - Astrophys. J., 584, 339-356 (2003/February-2)

Some diffuse interstellar bands related to interstellar C2Molecules.

THORBURN J.A., HOBBS L.M., McCALL B.J., OKA T., WELTY D.E., FRIEDMAN S.D., SNOW T.P., SONNENTRUCKER P. and YORK D.G.

Abstract (from CDS):

We have investigated the correlations between the equivalent widths of 21 selected diffuse interstellar bands (DIBs) and the corresponding interstellar column densities N(C2), N(CN), and N(CH), toward 53 stars with color excesses 0.11≤E(B-V)≤1.99. The observational data were derived primarily from echelle spectra acquired at R=38,000 as part of our extensive, continuing survey of the bands. All but six of the 53 final spectra show signal-to-noise ratios ≥800 at 5780 Å. The principal result presented here is that seven of the 21 bands prove to be examples of the C2DIBs'', a class of weak, narrow bands whose normalized equivalent widths Wλ(X)/Wλ(λ6196) are well correlated specifically with N(C2)/E(B-V) via power laws. In contrast, the similarly normalized equivalent widths of the 14 other, well-known DIBs analyzed here are uncorrelated, or weakly anticorrelated, with N(C2)/E(B-V), to within the observational uncertainties. Thus, the polyatomic molecule(s) presumed to cause these seven C2DIBs may bear a direct chemical relation to C2that is not shared by the polyatomic molecules putatively responsible for the other 14 bands. The C2DIBs also show positive correlations with N(CN)/E(B-V) and N(CH)/E(B-V) in our particular sample of light paths, although generally with shallower slopes in the case of N(CN) and with greater scatter in the case of N(CH). Eleven additional C2DIBs are also identified but are not analyzed here. Among the 18 C2DIBs identified, four apparently have not been previously detected. The λ4963 band is generally the strongest of the 18 C2DIBs, while the λ4734 band shows the most sensitive correlation with N(C2).