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M. Clampin (STScI), N. Panagia (STScI/ESA), L. Bergeron (STScI), A. Nota (STScI/ESA), A. Pasquali (ESO), R.E Schulte-Ladbeck (U. Pittsburgh)
We present a high resolution extinction map of the Eta Carinae nebula, obtained by combining HST optical WFPC2 (H\alpha, H\beta) and IR NICMOS images (Br\gamma, Pa\alpha). For the Homunculus, where gas and dust are mixed, the best way to determine relative extinctions is to use hydrogen line intensity ratios. For electron densities below ~ 1010~cm-3 the population of hydrogen levels is dominated by recombination processes and, therefore, the intensities of emission lines are weak functions of the electron temperature and their ratios are almost independent of temperature. The situation is more complicated in the presence of dust scattering, which introduces uncertainties in the true properties of the emitting photons. However, these problems are much less severe in the infrared than in the optical because both the albedo and the extinction cross section are smaller in the infrared. Therefore, the combination of optical and IR hydrogen lines has allowed us to construct an accurate extinction map of the nebula, which will be crucial in the understanding of its true three dimensional structure.
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