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D. E. Welty (Univ. of Chicago), J. T. Lauroesch (Northwestern Univ.), L. M. Hobbs, D. G. York (Univ. of Chicago)
We report initial results from analyses of HST/STIS echelle spectra of interstellar absorption toward the LMC stars Sk-67 5 and Sk-70 115, which are located in regions characterized by differences in UV extinction. In the main LMC components toward Sk-67 5, the depletions of Si, Mg, Fe, and Ni (relative to Zn) all are similar to those found for warm, diffuse clouds in the Galactic disk or halo. The main LMC component group toward Sk-70 115, however, exhibits both very mild depletions of Si and Mg and very severe depletions of Fe and Ni --- a pattern reminiscent of the depletions seen (thus far) in the SMC but not (as yet) in any Galactic sightline. In the NW part of the LMC near Sk-67 5, the UV extinction appears to be similar to the ``typical'' LMC curve. In the LMC2 region near Sk-70 115, however, the UV extinction has a somewhat steeper far-UV rise and a much weaker 2175 A bump --- more similar to the curves found toward most SMC targets. While the 2175 A bump is usually attributed to carbonaceous grains, these (limited) data raise the intriguing possibility of a connection between anomalously mild depletions of Si and weak 2175 A bumps --- as seen both in the SMC and in the LMC2 region.
Support for this work has been provided by NASA through grant HST-GO-09757.01-A (administered by STScI) and through LTSA grant NAG5-11413 (both to the University of Chicago).
The author(s) of this abstract have provided an email address for comments about the abstract: welty@oddjob.uchicago.edu
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Bulletin of the American Astronomical Society, 36 5
© 2004. The American Astronomical Society.