An Interstellar Conduction Front within a Wolf‐Rayet Ring Nebula Observed with the Goddard High Resolution Spectrograph

With the High Resolution Spectrograph aboard the Hubble Space Telescope weobtained high signal-to-noise (S/N > 200 - 600 per 17 km/s resolution element)spectra of narrow absorption lines toward the Wolf-Rayet star HD 50896. Thering nebula S308 that surrounds this star is thought to be caused by apressure-driven bubble bounded by circumstellar gas (most likely from a redsupergiant or luminous blue variable progenitor) pushed aside by a strongstellar wind. Our observation has shown for the first time that blueshifted(approximately 70 km/s relative to the star) absorption components of C IV andN V arise in a conduction front between the hot interior of the bubble and thecold shell of swept-up material. These lines set limits on models of theconduction front. Nitrogen in the shell appears to be overabundant by a factor~10. The P Cygni profiles of N V and C IV are variable, possibly due to asuspected binary companion to HD 50896.Comment: 32 pages, Latex, to appear in the Astrophysical Journal, April, 199