SPECTRAL IMAGING OF THE 3.3 AND 11.3 MICRON EMISSION BANDS IN NGC-1333 - DISCOVERY OF SPATIALLY SEPARATE BAND EMISSIONS

Spectral images and aperture spectra were obtained of the nebula around the star SVS 3 in the star formation region NGC 1333. The spectra contain strong infrared emission bands originating from carbonaceous material. The spectra show the presence of the characteristic 3.3 and 11.3 mum emission features thought to be associated with C-H stretching and C-H out-of-plane bending modes, respectively, of polycyclic aromatic hydrocarbons (PAHs). The distribution of the 3.3 mum emission is suggestive of limb brightening from the edge of an emitting shell. The 3.3 and 11.3 mum emission features come from spatially distinct regions, with the 3.3 mum emission occurring outside the region of strongest 11.3 mum emission. Thus, the relative band strengths cannot be used to determine the excitation temperature and average size of the molecules. The relative distributions of the 3.3 and 11.3 mum emission features can be understood if the bands arise from PAH molecules of different sizes. Spectra in the 3 mum region of 4 positions around SVS 3, which sample regions of similar excitation, show 3.3 and 3.4 mum emission bands with the same relative intensities. The data mildly favor the identification of the 3.4 mum band with an excited mode of the C-H stretch (i.e., a hot band) or an overtone/combination rather than with the presence of molecular side groups on the PAHs, since the spectra are identical yet sample physically separate regions.