ASTRO-2 OBSERVATIONS OF INTERSTELLAR DUST AND GAS IN THE LARGE MAGELLANIC CLOUD

摘要

This paper presents the first UV (1400-3200 A) polarimetry and far-UV (950-1200 A) spectrophotometry ever obtained for reddened stars in the Large Magellanic Cloud (LMC). We derive the UV wavelength dependence of interstellar polarization down to 1400 A and that of extinction down to near the Lyman limit. We also measure column densities of H_2 along these lines of sight in the LMC. We have obtained these data with the Hopkins Ultraviolet Telescope (HUT) and the Wisconsin Ultraviolet Photo-Polarimeter Experiment (WUPPE) using the Astro-2 Observatory, which flew on the Space Shuttle in 1995 March. The UV interstellar polarization in the LMC shows a wavelength dependence similar to that seen in the Galaxy. The magnitude of the polarization in the UV lies on or above an extrapolation of the Ser-kowski curve. This is consistent with the wavelength dependence seen for low λ_(max) sight lines in the Galaxy. The far-UV extinction in the LMC continues to rise to 10.5 μm~(-1), which confirms that large numbers of small grains are present. The measured column densities of H_2 with respect to H Ⅰ are low compared to the Galaxy and track the previously measured lower dust abundance. The H_2 abundance may be regulated by the amount of dust present. These new data will allow a comparison of how interstellar dust properties vary in different galactic environments.