FUSE OBSERVATIONS OF HIGHLY IONIZED GAS IN THE VELA SUPERNOVA REMNANT

摘要

We present Far Ultraviolet Spectroscopic Explorer (FUSE) data on O Ⅵ absorption lines observed toward nine stars behind the Vela supernova remnant (SNR). The O Ⅵ observations are compared with International Ultraviolet Explorer (IUE) observations of C Ⅳ absorption toward the same stars. All of these stars are B stars, which generally have complex continua, making the extraction of absorption lines difficult. However, four of the stars, HD 72088, HD 72089, HD 72350, and HD 72537, are rapid rotators (v sin I approx> 150 km s~(-1)), making the derivation of absorption column densities much easier. We present O Ⅵ and C Ⅵ column densities for the "main component" (I.e., the low-velocity component) for these stars. In the FUSE spectra of three of the rapid rotators (HD 72088, HD 72089, and HD 72537) we find high-velocity components of O Ⅵ at ～150 km s~(-1) that we attribute to the SNR shock. HD 72350 has very strong H_2 absorption, which obscures any possible high-velocity O Ⅵ absorption. To detect the high-velocity O Ⅵ absorption in HD 72088 requires employing a technique for removing the H_2 line at 1032.35 A (121.6 km s~(-1) relative to O Ⅵ). The O Ⅵ data are consistent with steady radiative shock models with v_s ≈ 150 km s~(-1), but we do not detect C Ⅳ at the same velocities. Instead we find high-velocity C Ⅳ at lower velocities (～ 100 km s~(-1)). We discuss the implications of our results for models of the evolution of the Vela SNR.