A high spatial resolution map of η Carinae at 2.2 μm is presented. The map, in which a beam width (FWHM) of 1".1 was employed, shows that the previously identified double-peaked nature of the inner region of the homunculus in the wavelength range 3.6-11.2 μm is also strongly evident at 2.2 μm. Comparison with previous results shows the secondary maximum to be relatively more intense at 2.2 μm than at 3.6 μm. A consideration of the volume emission coefficients for thermal emission and scattering reveals, rather surprisingly, that at 2.2 μm the secondary source is likely to be due to thermal emission by dust grains rather than to scattering, which is responsible for the visible reflection nebula. If so, the data imply a difference in the near-infrared dust emissivity in the regions producing the two peaks. In particular, the material in the secondary shows evidence for a more steeply decreasing emissivity toward longer wavelengths than in the primary, possibly implying an enhancement of "clean" silicate material in the secondary. A consideration of the morphology of the homunculus confirms that η Car may be viewed as an extremely luminous bipolar nebula. It is suggested that accretion onto a massive star may explain both the nineteenth century outburst and the bipolar characteristics of the mass loss nebula.
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Mitchell et al. (1983) studied this question.