Starburst‐like Dust Extinction in the Small Magellanic Cloud

The recent discovery that the UV dust extinction in starburst galaxies issimilar to that found in the Small Magellanic Cloud (SMC) motivated us tore-investigate the ultraviolet (UV) extinction found in the SMC. We have beenable to improve significantly on previous studies by carefully choosing pairsof well matched reddened and unreddened stars. In addition, we benefited fromthe improved S/N of the NEWSIPS IUE data and the larger sample of SMC stars nowavailable. Searching the IUE Final Archive, we found only four suitableearly-type stars that were significantly reddened and had well matchedcomparison stars. The extinction for three of these stars is remarkablysimilar. The curves are roughly linear with 1/lambda and have no measurable2175 A bump. The fourth star has an extinction curve with a significant 2175 Abump and weaker far-UV extinction. The dust along all four sightlines isthought to be local to the SMC. There is no significant Galactic foregroundcomponent. The first three stars lie in the SMC Bar and the line-of-sight foreach of them passes through regions of recent star formation. The fourth starbelongs to the SMC Wing and its line-of-sight passes though a much morequiescent region. Thus, the behavior of the dust extinction in the SMC supportsa dependence of dust properties on star formation activity. However, otherenvironmental factors (such as galactic metallicity) must also be important.Dust in the 30 Dor region of the LMC, where much more active star formation ispresent, does not share the extreme extinction properties seen in SMC dust.Comment: 23 pages, figures included, to be published in the ApJ (20 June 1998