98 06 02 0 v 1 1 J un 1 99 8 Interstellar Absorption Lines in the spectrum of the starburst galaxy NGC 1705

I present a GHRS archival study of the interstellar absorption lines in the line-of-sight to the H i-rich starburst dwarf galaxy NGC 1705, in the λ1170 to 1740 Å range at ∼ 120 km s resolution. The absorption features arising due to photospheric lines are distinctly different from the interstellar lines : the photospheric lines are weak, broad (equivalent widths > 1Å), asymmetric and centred around the systemic LSR velocity of NGC 1705 (∼ 610 km s). The interstellar lines consist of three relatively narrow components at LSR velocities of –20, 260 and 540 km s and include absorption by neutral atoms (N i λ1200 Å triplet and O i λ1302 Å) singly ionized atoms (Si ii λ1190, 1193, 1260, 1304 and 1526 Å, S ii λ1253 Å, C ii λ1334 Å, C ii λ1336 Å, Fe ii λ1608 Å and Al ii λ1670 Å) and atoms in higher ionization states (Si iii λ1206 Å, Si iv λ1393, 1402 Å and C iv λ1548, 1550 Å). The Si iv and C iv absorption features have both interstellar and photospheric contributions. In an earlier study, Sahu & Blades (1997) identified the absorption system at –20 km s with Milky Way disk/halo gas and the 260 km s system with a small, isolated high-velocity cloud HVC 487, which is probably associated with Magellanic Stream gas. The 540 km s absorption system is associated with a kpc-scale expanding, ionized supershell centred on the superstar cluster NGC 1705-1. The analysis presented in this paper consists of (1) a list of all interstellar absorption features with > 3 σ significance and their measured equivalent widths and (2) plots of the lines in the various atomic species together with the results of non-linear least square fit profiles to the observed data and (3) unpublished 21-cm maps from the Wakker & van Woerden survey showing the large-scale H i distribution in the region near the NGC 1705 sightline and HVC 487. Further, I report weak N i λ1200 Å triplet absorption for the supershell component, which in the absence of dust depletion and