THE ASTROPHYSICAL JOURNAL, 558:133È144, 2001 September 1 ( 2001. The American Astronomical Society. All rights reserved. Printed in U.S.A. FAR UL T RAV IOL ET SPECT ROSCOPIC EXPL ORER OBSERVATIONS OF INTERSTELLAR GAS TOWARD THE SMALL MAGELLANIC CLOUD STAR SK 108 C. MALLOURIS,1 D. E. WELTY,1 D. G. YORK,1,2 H. W. MOOS,3 K. R. SEMBACH,3 S. D. FRIEDMAN,3 E. B. JENKINS,4 M. LEMOINE,5 W. R. OEGERLE,3 B. D. SAVAGE,6 J. M. SHULL,7 G. SONNEBORN,8 AND A. VIDAL-MADJAR9 Received 2001 February 8 ; accepted 2001 May 4 ABSTRACT We discuss the interstellar absorption lines found in Far Ultraviolet Spectroscopic Explorer spectra of the Wolf-Rayet binary Sk 108, which is located in the northeastern part of the main ““ bar ÏÏ of the Small Magellanic Cloud. The spectra cover the 988È1187 wavelength range at a resolution of about 12,000 A  and a signal-to-noise ratio of 20È 40. We use detailed component information from higher resolution near-UV and optical spectra to model the far-UV lines of similarly distributed species. Both the Galactic and SMC gas toward Sk 108 seem to be predominantly neutral, although a signiÐcant fraction of the SMC gas is ionized. The column densities of P II,S II, and Ar I are consistent with essentially solar ratios, relative to N(Zn II), in both the Galactic and SMC gas ; the column density of N I remains some- what uncertain. Molecular hydrogen is present in the Galactic gas, with properties similar to those found in low mean density Galactic lines of sight and in the Galactic gas toward several other LMC and SMC stars. We report a tentative detection of in the SMC gas for J \ 1 and 3, with rotational level popu- H 2 lations consistent with an excitation temperature on the order of 1000 KÈsimilar to the found in H 2 di†use Galactic gas toward f Puppis. Strong absorption from N III,S III, and Fe III has revealed a signiÐ- cant ionized component, particularly in the SMC ; O VI is present, but relatively weak, especially in the Galactic gas. The N(C IV)/N(O VI) ratio varies somewhat within the SMC, suggesting that several pro- cesses may contribute to the observed high ion abundances. Subject headings : galaxies : abundances È galaxies : ISM È ISM : abundances È Magellanic Clouds È stars : individual (Sk 108) 1. INTRODUCTION The observed subsolar gas-phase abundances [X/H] of most heavy elements in the Galactic interstellar medium (ISM) are usually taken to indicate that the ““ missing ÏÏ atoms have been depleted into dust grains that generally are coextensive with the gas (see, e.g., Jenkins 1987 ; Savage & Sembach 1996). Observations of heavy elements in quasi- stellar object (QSO) absorption-line systems (ALSs), which likely sample the ISM of galaxies of various kinds at various evolutionary stages, may provide the best means of tracing the buildup of those elements for redshifts if z [ 5, the possible (or likely !) e†ects of depletion and ionization can be assessed (see, e.g., Lu et al. 1996 ; Lauroesch et al. 1996 ; Pettini et al. 1997 ; Prochaska & Wolfe 1997). Howk & Sembach (1999) have explored the e†ects of the presence of some ionized gas on the elemental abundances inferred for QSOALSs. Several other recent studies have attempted 1 University of Chicago, Department of Astronomy and Astrophysics, 5640 South Ellis Avenue, Chicago, IL 60637. 2 Enrico Fermi Institute, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637. 3 Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218. 4 Princeton University Observatory, Peyton Hall, Princeton, NJ 08544. dÏAstrophysique Relativiste et de Cosmologie, UMR- 5 De partement 8629 CNRS, Observatoire de Paris-Meudon, Place Jules Janssen, F-92195 Meudon, France. 6 Department of Astronomy, University of Wisconsin at Madison, 475 North Charter Street, Madison, WI 53706. 7 Center for Astrophysics and Space Astronomy, Department of Astro- physical and Planetary Sciences, University of Colorado, Campus Box 389, Boulder, CO 80309. 8 Laboratory for Astronomy and Solar Physics, NASA Goddard Space Flight Center, Code 681, Greenbelt, MD 20771. 9 Institut dÏAstrophysique de Paris, CNRS, 98 bis Boulevard Arago, F-75014 Paris, France. to ascertain the underlying total abundance patterns (and thus the nucleosynthetic histories) of some QSOALSs by adjusting the observed gas-phase abundances for an assumed level and pattern of depletion (see, e.g., Kulkarni, Fall, & Truran 1997 ; Vladilo 1998). Such studies depend, however, on the assumption that the dust depletion pat- terns found in our own Galactic ISM also are appropriate for the lower metallicity QSOALSs. Studies of the abun- dances and physical conditions in the ISM of the Magella- nic CloudsÈnearby systems of low metallicity and low dust-to-gas ratio (similar to some QSOALSs) for which stellar abundance data are also availableÈcan provide a signiÐcant test of that assumption. UV spectra of the SMC Wolf-Rayet binary Sk 108, obtained with the Hubble Space T elescope (HST ) Goddard High Resolution Spectrograph (GHRS), have yielded the most extensive and accurate abundances currently available for the SMC ISM (Welty et al. 1997, hereafter Paper I). Fits to the GHRS echelle proÐles of absorption lines due to Si II, Mn II, and Fe II toward Sk 108 required (at least) 25 com- ponents, which were grouped into Ðve sets based on kine- matics and/or relative abundances. One set of components (G1, at [6 to 6 km s~1) arises in the Galactic halo, one set (G2, at 13È57 km s~1) arises in the Galactic disk, and three sets (S1, at 95È156 km s~1 ; S2, at 167È196 km s~1 ; and S3, at 209È216 km s~1) are attributable to gas in the SMC. The total H I column densities, for both Galactic and SMC gas, are roughly 3.5 ] 1020 cm~2 (Fitzpatrick 1985), predomi- nantly in the G2 and S1 components. The halo components and the three SMC component groups all exhibit relative abundance patterns ([X/Zn] for X \ Si, Cr, Mn, Fe, and Ni) similar to those found in Galactic halo clouds ; the G2 components have abundances similar to those in warm, di†use clouds in the Galactic disk. The relative gas-phase 133