The relation between CH and CN molecules and carriers of 5780 and 5797 diffuse interstellar bands

Abstract

Optical absorption bands of the interstellar CN (near 3875 Å) and CH molecules (the violet and blue ones near 4300 and 3886 Å, respectively) were applied to determine the column densities of these two radicals in a statistically meaningful sample of 84 reddened OB stars. Equivalent widths of the major 5780 and 5797 diffuse bands (DIBs) were measured along the lines of sight toward the same stars in spectra acquired using four echelle spectrographs situated in both the northern and southern hemispheres. The mutual relation between abundances of CH and CN molecules shows a large scatter; and especially the CN molecule abundance varies strongly from cloud to cloud. The carriers of the major 5780 and 5797 DIBs seem to be spatially correlated with column densities of CH rather than of the CN molecule. This is most likely true in the case of a narrower feature: the 5797 DIB correlates with CH column density better than 5780 does. The correlations do suggest that the DIB carriers are likely hydrocarbons. They apparently occupy molecular clouds since the H abundance is closely related to that of methylidyne (CH), as has already been demonstrated. © 2008 ESO.