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Keywords:

  • techniques: spectroscopic;
  • stars: individual: Red Rectangle;
  • ISM: abundances;
  • ISM: lines and bands;
  • ISM: molecules

ABSTRACT

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