STARBURST-LIKE DUST EXTINCTION IN THE SMALL-MAGELLANIC-CLOUD

The recent discovery that the ultraviolet (UV) dust extinction in star burst 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 ca refully choosing pairs of well-matched reddened and unreddened stars. In addition, we benefited from the improved signal-to-noise ratio of t he NEWSIPS International Ultraviolet Explorer (IUE) data and the large r sample of SMC stars now available. Searching the IUE Final Archive, we found only four suitable early-type stars that were significantly r eddened and had well-matched comparison stars. The extinction for thre e 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 thou ght to be local to the SMC. There is no significant Galactic foregroun d 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 formatio n. The fourth star belongs to the SMC wing, and its line of sight pass es through a much more quiescent region. Thus, the behavior of the dus t extinction in the SMC supports a dependence of dust properties on st ar formation activity. However, other environmental factors (such as g alactic metallicity) must also be important. Dust in the 30 Dor region of the LMC, where much more active star formation is present, does no t share the extreme extinction properties seen in SMC dust.