Hubble Space Telescope STIS Observations of the Wolf-Rayet Star HD 5980 in the Small Magellanic Cloud. II. The Interstellar Medium Components^*

Observations of the interstellar and circumstellar absorption components obtained with the Hubble Space Telescope Space Telescope Imaging Spectrograph (STIS) along the line of sight toward the Wolf-Rayet–luminous blue variable (LBV) system HD 5980 in the Small Magellanic Cloud are analyzed. Velocity components from C I, C I*, C II, C II*, C IV, N I, N V, O I, Mg II, Al II, Si II, Si II*, Si III, Si IV, S II, S III, Fe II, Ni II, Be I, Cl I, and CO are identified, and column densities estimated. The principal velocity systems in our data are (1) interstellar medium (ISM) components in the Galactic disk and halo (V_hel = 1.1 ± 3, 9 ± 2 km s^-1); (2) ISM components in the SMC (V_hel = +87 ± 6, +110 ± 6, +132 ± 6, +158 ± 8, +203 ± 15 km s^-1); (3) SMC supernova remnant SNR 0057-7226 components (V_hel = +312 ± 3, +343 ± 3, +33, +64 km s^-1); (4) circumstellar (CS) velocity systems (V_hel = -1020, -840, -630, -530, -300 km s^-1); and (5) a possible system at -53 ± 5 km s^-1 (seen only in some of the Si II lines and marginally in Fe II) of uncertain origin. The supernova remnant SNR 0057-7226 has a systemic velocity of +188 km s^-1, suggesting that its progenitor was a member of the NGC 346 cluster. Our data allow estimates to be made of T_e ∼ 40,000 K, n_e ∼ 100 cm^-3, N(H) ∼ (4–12) × 10¹⁸ cm^-2 and a total mass between 400 and 1000 M_⊙ for the supernova remnant (SNR) shell. We detect C I absorption lines primarily in the +132 and +158 km s^-1 SMC velocity systems. As a result of the LBV-type eruptions in HD 5980, a fast-wind/slow-wind circumstellar interaction region has appeared, constituting the earliest formation stages of a windblown H II bubble surrounding this system. Variations over a timescale of 1 year in this circumstellar structure are detected.