ULTRAVIOLET INTERSTELLAR ABSORPTION-LINES TOWARD THE STARBURST DWARF GALAXY NGC-1705

Archival Goddard High Resolution Spectrograph (GHRS) low-resolution sp ectra of NGC 1705, with wavelength ranges of 1170.3-1461.7 Angstrom an d 1453.5-1740.1 Angstrom and a velocity resolution of similar to 120 k ms(-1), have been used to derive the velocity structure and equivalent widths of the absorption lines of Si II lambda 1190.42, lambda 1260.4 2, lambda 1304.37, and lambda 1526.71, S II lambda 1253, Al II lambda 1670.79, and Fe II lambda 1608.45 in this sight line. Three relatively narrow absorption components are seen at LSR velocities of -20 kms(-1 ), 260 kms(-1), and 540 kms(-1). Arguments are presented to show that these absorption features are interstellar rather than stellar in orig in on the basis of a comparison with the C III lambda 1175.7 absorptio n feature. We identify the -20 kms(-1) component with Milky Way disk a nd halo gas and the 260 kms(-1) component with an isolated high-veloci ty cloud, HVC 487. This small HVC is located similar to 10 degrees fro m the H I gas that envelops the Magellanic Clouds and the Magellanic S tream (MS). The Si/H ratio for this HVC is greater than 0.6(Si/H)., wh ich with velocity agreement suggests association with the Magellanic C loud and MS gas. H alpha emission line kinematics of NGC 1705 show the presence of a kiloparsec-scale expanding supershell of ionized gas ce ntered on the central nucleus with a blueshifted emission component at 540 kms(-1). We identify the 540 kms(-1) absorption component seen in the GHRS spectra with the front side of this expanding, ionized super shell. The most striking feature of this component is strong Si II and Al II absorption but weak Fe II lambda 1608 absorption. The low Fe II column density derived is most likely intrinsic since it cannot be ac counted for by ionization corrections or dust depletion. Because of th eir shallow gravitational potential wells, dwarf galaxies have small g ravitational binding energies and are vulnerable to large mass losses from strong winds driven by the supernovae from the first generation o f stars. Galactic winds from dwarf galaxies occur at timescales less t han 10(8) yr, which is less than the timescale required to produce Typ e Ia supernovae. Consistent with our observations, shells produced by galactic winds are expected to be enriched with Type II supernova prod ucts like Si, Al, and Mg and should be deficient in the products of Ty pe Ia supernovae, like Fe and iron-peak elements.