2019ApJ...886..138A

The emission spectra of the λ5800 Red Rectangle Band (RRB) are simulated at all regions of the Red Rectangle Nebula, utilizing a polar carbon chain model previously developed for the λ5797.1 diffuse interstellar band (DIB) in absorption in the interstellar medium. If high radiative temperatures are assumed, radiative pumping of numerous rotational J levels of a polar (µ = 4 D) carbon chain whose rotational constant B = 1200 MHz decreases by 3% upon electronic excitation produces an emission spectrum with a sharp blue edge and an extended tail toward the red (ETR). This ETR broadens with increasing temperature, resembling the behavior of the λ5800 RRB. It is shown that subsequent self-absorption in the foreground of the nebula can saturate the lower-wavelength emission to redshift the peak wavelengths of the simulated emission profiles, reproducing the observed λ5800 RRB sequence structure. The requirement of high column densities of DIB absorbers in the nebula presents one difficulty with this model. If overcome, the simulations present empirical evidence that the λ5797.1 DIB and the λ5800 RRB can originate from identical carrier molecules.