Spatial distribution and interpretation of the 3.3 μm PAH emission band of the Red Rectangle

The spatial distribution of 3.3m polycyclic aromatic hydrocarbon (PAH) and associated emission in the inner region of the Red Rectangle nebula has been determined using the UIST imager spectrometer at the United Kingdom Infrared Telescope (UKIRT). Interpretation of the 3.3m feature as comprising two spectroscopic components centred at 3.30 and 3.28m, as put forward by Song et al., is supported by these data which reveal that they have different spatial distributions. It is deduced that there are two classes of 3.3m band carrier with a peak wavelength separation of ∼0.02m. From comparison of the 3.3m observations with laboratory and theoretical spectra for a range of PAH molecules, it is proposed that the 3.28 and 3.30m components arise from ‘bay’ and ‘non-bay’ hydrogen sites, respectively, on the periphery of small neutral PAHs. Observational data are also obtained for L-band continuum emission and for the Pfund ɛ hydrogen recombination line.