Evidence for a link between the more prominent optical emission bands in the Red Rectangle and some of the diffuse interstellar absorption bands

A re-examination of the spectra of the nebulosity in the Red Rectangle (RR) shows that the wavelengths of the four most prominent emission bands correspond closely with one of the proposed families of diffuse interstellar absorption bands (DIBs). At large offset distances (cooler conditions) from the A0–B8 central star (HD 44179), the emission bands become quite narrow and both the peak wavelengths and widths extrapolate to the observed values for the corresponding DIBs; this suggests that each pair of the corresponding RR/DIB bands belongs to a common carrier. These emission and absorption features are discussed in terms of electronic transitions in gas-phase molecules.