Hubble Space Telescope STIS observations of the Wolf-Rayet star HD 5980 inthe Small Magellanic Cloud. II. The interstellar medium components

Observations of the interstellar and circumstellar absorption components ob tained with the Hubble Space Telescope Space Telescope Imaging Spectrograph (STIS) along the line of sight toward the Wolf-Rayet-luminous blue variabl e (LBV) system HD 5980 in the Small Magellanic Cloud are analyzed. Velocity components from C I, CI *, C II, CII *, C IV, NI, 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 sys tems in our data are (1) interstellar medium (ISM) components in the Galact ic 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)); (#) SMC supernova remnant SNR 0057 - 7226 components (V-hel = +312 +/- 3, +343 +/- 3, +33, +64 km s(-1)); (4) circumstellar (CS) veloci ty systems (V-hel = -1020, -840, -630, -530, -300 km s(-1)); and (%) a poss ible system at -53 +/- 5 km s-1 (seen only in some of the Si II lines and m arginally in Fe II) of uncertain origin. The supernova remnant SNR 0057 - 7 226 has a systemic velocity of +188 km s(-1), suggesting that its progenito r was a member of the NGC 346 cluster. Our data allow estimates to be made of T-e similar to 40,000 K, n(e) similar to 100 cm(-3), N(H) similar to (4- 12) x 10(18) cm(-2) and a total mass between 400 and 1000 M-. for the super nova remnant (SNR) shell. We detect C I absorption lines primary in the +13 2 and +158 km s(-1) SMC velocity systems. As a result of the LBV-type erupt ions in HD 5980, a fast-wind/slow-wind circumstellar interaction region has appeared, constituting the earliest formation stages of a windblown H II b ubble surrounding this system. Variations over a timescale of 1 year in thi s circumstellar structure are detected.