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U. J. Sofia (Whitman), K. D. Gordon (Steward Obs.), G. C. Clayton (LSU), K. Misselt (Steward Obs.), M. J. Wolff (SSI), N. L. J. Cox (U. Amsterdam), P. Ehrenfreund (Leiden Obs.)
We explore the interstellar abundances and depletion levels in the Small Magellanic Cloud (SMC) sight lines toward AzV 18, AzV 456, Sk 108 and Sk 155, observed with the Hubble Space Telescope. In contrast to previous studies, we find evidence that silicon is depleted in the SMC's interstellar medium. This makes it improbable that SMC-like extinction results from a lack of silicate grains in the SMC. Notable differences between our sight lines that have SMC-like and Milky Way-like extinction, AzV 18 and AzV 456, respectively, are that the former has a substantially larger gas-to-dust ratio and smaller fractional H2 abundance. Iron abundances and depletions in the SMC's interstellar medium often diverge from the pattern shown by Si and Mg. This is evidence that Fe is not tied to the same grains as silicon and is probably incorporated into grain types such as metals or oxides. This work was supported by the Space Telescope Science Institute (GO-9383).
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.