Phillips, J. P.; White, Glenn J.; Richardson, K. J. and Williams, P. M.
High resolution infrared spectroscopy of W51-IRS2.
In: Galactic and Extragalactic Infrared Spectroscopy, 03-04 December 1981, Leiden, pp. 73–75.
Spectra were obtained of W51-IRS2 in the wavelength ranges 2.95-3.5 μm, and 3.99-4.1 μm. These show the presence of the Pf epsilon and Br alpha recombination lines of HI, and the 3.28 μm narrow band emission feature. Sampling of Br alpha and the 3.28 μm feature northwards of IRS-2 shows emission to be in both cases extended over radial distances 20 arc seconds. In the case of Br alpha, we interpret this to arise in a blister region of density or approximately 103 cm-3. For the 3.28 μm feature, we demonstrate that observed band strengths are consistent with the Dweck et al. (1980) hypothesis of thermal excitation, providing that the oscillators responsible for this emissions are located within one extinction optical depth of the HI/HII interface.
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