Ultraviolet absorption by interstellar gas near 30 Doradus

The International Ultraviolet Explorer was used to obtain high-resolution (lambda/Δlambdaapprox.1.2 x 104), far-UV spectra (lambdalambdaapprox.1150--2070 A) of two stars in the 30 Doradus H II region in the large Magellanic Cloud. In these spectra we can distinguish interstellar absorption components at heliocentric velocities of +20, +220, +250, and +290 km s-1. The +20 km s-1 component is produced by matter in our Galaxy. The high-velocity components are produced by absorbing gas in or near the LMC. The species detected include: H I, C I, C I*, C II, C II*, C IV, N I, O I, O I*, Mg I, Mg II, Al II, Al III, Si II, Si II*, Si IV, S II, Cr II, Fe II, Ni II, and Zn II. From the velocity pattern of the observed LMC features, a model for the line-of-signt distribution of the absorbing clouds is developed. From Lα we infer a gas-to-dust ratio for material in the 30 Dor region four times larger than the average galactic value. In the 290 km s-1 cloud, gaseous Si and O have abundances similar to those found in galactic interstellar gas, in agreement with results from emission-line studies of 30 Dor. The lines of Si IV and C IV seen at radial velocities as small as 180 km s-1 could indicate a halo of ionized gas around the LMC, similar to the galactic corona discovered from the same spectra by Savage and de Boer