SWS spectra of three carbon-rich evolved stars, the post-AGB star HR 4049 and two planetary nebulae, IRAS21282+5050 and NGC7027. The dashed lines indicate the location of the continuum. The emission bands are attributed to the stretching and bending modes of C-C and C-H bonds in Polycyclic Aromatic Hydrocarbons (PAHs).
This image was taken from the ISO dedicated Astronomy and Astrophysics Letter;
"The rich spectrum of circumstellar PAHs", D.A. Beintema et al.