Fuse measurements of far-ultraviolet extinction. I. Galactic sight lines

We present extinction curves that include data down to far- ultraviolet wavelengths ( FUV; 1050 - 1200 angstrom) for nine Galactic sight lines. The FUVextinction was measured using data from the Far Ultraviolet Spectroscopic Explorer. The sight lines were chosen for their unusual extinction properties in the infrared through the ultraviolet; that they probe a wide range of dust environments is evidenced by the large spread in their measured ratios of total to selective extinction, R-V = 2: 43 3: 81. We find that extrapolation of the Fitzpatrick & Massa relationship from the ultraviolet appears to be a good predictor of the FUVextinction behavior. We find that predictions of the FUVextinction based on the Cardelli, Clayton, & Mathis ( CCM) dependence on RV give mixed results. For the seven extinction curves well represented by CCM in the infrared through ultraviolet ( x < 8 mu m (-1)), the FUVextinction is well predicted in three sight lines, overpredicted in two sight lines, and underpredicted in two sight lines. A maximum entropy method analysis using a simple three- component grain model shows that seven of the nine sight lines in the study require a larger fraction of grain materials to be in dust when FUVextinction is included in the models. Most of the added grain material is in the form of small ( radii <= 200 angstrom) grains.