Starburst‐like Dust Extinction in the Small Magellanic Cloud

Abstract

The recent discovery that the ultraviolet (UV) dust extinction in starburst galaxies is similar to that found in the Small Magellanic Cloud (SMC) motivated us to reinvestigate the UV extinction found in the SMC. We have been able to improve signiÐcantly on previous studies by carefully choosing pairs of well-matched reddened and unreddened stars. In addition, we beneÐted from the improved signal-to-noise ratio of the NEWSIPS International Ultraviolet Explorer (IUE) data and the larger sample of SMC stars now available. Searching the IUE Final Archive, we found only four suitable early-type stars that were signiÐcantly reddened and had well-matched comparison stars. The extinction for three of these stars is remarkably similar. The curves are roughly linear with j~1 and have no measurable 2175 bump. The fourth star has an extinction curve with a signiÐcant 2175 bump and weaker far-UV A Ž A Ž extinction. The dust along all four sight lines is thought to be local to the SMC. There is no signiÐcant Galactic foreground component. The Ðrst three stars lie in the SMC bar, and the line of sight for each of them passes through regions of recent star formation. The fourth star belongs to the SMC wing, and its line of sight passes through a much more quiescent region. Thus, the behavior of the dust extinction in the SMC supports a dependence of dust properties on star formation activity. However, other environ-mental factors (such as galactic metallicity) must also be important. Dust in the 30 Dor region of the LMC, where much more active star formation is present, does not share the extreme extinction proper-ties seen in SMC dust.