THE NEBULAR EXTINCTION IN THE ORION-NEBULA

We examine the nebular extinction in the Orion Nebula using a combination of new near-infrared (1.2-2.4 mu m) and previously published optical (0.34-1.0 mu m) spectrophotometry. Using the emission lines of the H I Balmer, Paschen, and Brackett recombination series, and assuming case B recombination and the stellar extinction law, we obtain discrepant estimates of the total extinction, A(V), in which the derived A(V) increases with the wavelength of the series being considered. This discrepancy is inconsistent with expected small deviations from case B recombination theory. We suggest instead that it is mostly a consequence of optical effects due to the complex distribution of gas and dust in the nebula. We derive a empirical effective nebular extinction law for the ionized hydrogen zone of the nebula and use this extinction law to deredden the observed emission-line ratios to assess the impact of our nebular extinction treatment on dust-sensitive emission-line diagnostics of temperature and ionic abundances.