UV Extinction in the 30 Doradus Nebula and the UV Energy Distribution of R136a

Abstract

The properties of ultraviolet interstellar extinction in and near the core of the 30 Doradus Nebula are studied. The pair method is employed using nine reddened stars from within 5′ (80pc) of the core and nine unreddened stars from a variety of locations in the large Magellanic Cloud. All of the 30 Doradus stars examined appear to be reddened by E(B-V) ⋍ 0.12 with an extinction law similar in wavelength dependence to those derived for the LMC by Koornneef and Code (1981) and Nandy et al. (1981). Several of the stars, including R136a, R145 and R147, are found to be additionally reddened by E(B-V) ⋍ 0.18 with an extinction law qualitatively similar in wavelength dependence to the law found in the Orion region. A two-component model, featuring a layer of “LMC foreground dust” which affects all of the stars and a deeper layer of “nebular dust” which affects some of the stars, provides the simplest explanation of the extinction properties. The 2200 Å extinction bump is present in both curves. The wavelength positions of the bump and the bump profiles, when normalized to a linear “background extinction”, are indistinguishable from the average Galactic bump. The strengths of the bumps, relative to E(B-V), are 20–30% weaker than for the Milky Way Curve.