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


E-mail: (AC); (PJS)


The spatial distribution of 3.3math formulam polycyclic aromatic hydrocarbon (PAH) and associated emission in the math formula 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 3.3math formulam feature as comprising two spectroscopic components centred at 3.30 and 3.28math formulam, 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 3.3math formulam band carrier with a peak wavelength separation of ∼0.02math formulam. From comparison of the 3.3math formulam observations with laboratory and theoretical spectra for a range of PAH molecules, it is proposed that the 3.28 and 3.30math formulam 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.