ITAL]Far Ultraviolet Spectroscopic Explorer[/ITAL] Observations of a Supernova Remnant in the Line of Sight to HD 5980 in the Small Magellanic Cloud

Abstract

We report a detection of far-ultraviolet absorption from the supernova remnant SNR 0057-7226 in the Small Magellanic Cloud (SMC). The absorption is seen in the Far Ultraviolet Spectroscopic Explorer (FUSE) spectrum of the luminous blue variable/Wolf-Rayet star HD 5980. Absorption from O VI λ1032 and C III λ977 is seen at a velocity of 300 km s-1 with respect to the Galactic absorption lines, 170 km s-1 with respect to the SMC absorption. The O VI λ1038 line is contaminated by H2 absorption but is present. These lines are not seen in the FUSE spectrum of Sk 80, only ~1' (~17 pc) away from HD 5980. No blueshifted O VI λ1032 absorption from the SNR is seen in the FUSE spectrum. The O VI λ1032 line in the SNR is well described by a Gaussian with FWHM = 75 km s-1. We find log N(O ) = 14.33-14.43, which is roughly 50% of the rest of the O VI column in the SMC (excluding the SNR) and greater than the O VI column in the Milky Way halo along this sight line. The N(C IV)/N(O VI) ratio for the SNR absorption is in the range of 0.12-0.17, similar to the value seen in the Milky Way disk and lower than the halo value, supporting models in which SNRs produce the highly ionized gas close to the plane of the Galaxy, while other mechanisms occur in the halo. The N(C IV)/N(O VI) ratio is also lower than the SMC ratio along this sight line, suggesting that other mechanisms contribute to the creation of the global hot ionized medium in the SMC. The O VI, C IV, and Si IV apparent column density profiles suggest the presence of a multiphase shell followed by a region of higher temperature gas.