Starburst-like dust extinction in the Small Magellanic Cloud

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 significantly on previous studies by carefully choosing pairs of well-matched reddened and unreddened stars. In addition, we benefited 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 significantly reddened and had well-matched comparison stars. The extinction for three of these stars is remarkably similar. The curves are roughly linear with lambda(-1) and have no measurable 2175 Angstrom bump. The fourth star has an extinction curve with a significant 2175 Angstrom bump and weaker far-UV extinction. The dust along all four sight lines is thought to be local to the SMC. There is no significant Galactic foreground component. The first 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 environmental 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 properties seen in SMC dust.