2012MNRAS.426..389C

The spatial distribution of 3.3\mspacemum polycyclic aromatic hydrocarbon (PAH) and associated emission in the \mn 3.3\mspace\mi arcsec\mo x \mspace\mn 6.0\mspace \mi arcsec 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 3.3\mspacemum feature as comprising two spectroscopic components centred at 3.30 and 3.28\mspacemum, 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 3.3\mspacemum band carrier with a peak wavelength separation of ∼ 0.02\mspacemum. From comparison of the 3.3\mspace mum observations with laboratory and theoretical spectra for a range of PAH molecules, it is proposed that the 3.28 and 3.30\mspacemum 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{epsilon hydrogen recombination line.

Present address: Korea Science Academy of KAIST, 899 Danggam 3-dong, Busanjin-gu, Busan 614-822, Korea.