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 Telescop e we obtained high signal-to-noise ratio (S/N greater than or similar to 200-600 per 17 km s(-1) resolution element) spectra of narrow absor ption lines toward the Wolf-Rayet star HD 50896. The ring nebula S308 that surrounds this star is thought to be caused by a pressure-driven bubble bounded by circumstellar gas (most likely from a red supergiant or luminous blue variable progenitor) pushed aside by a strong stella r wind. Our observation has shown for the first time that blueshifted (approximate to 70 km s(-1) relative to the star) absorption component s of C IV and N V arise in a conduction front between the hot interior of the bubble and the cold shell of swept-up material. These lines se t limits on models of the conduction front. Nitrogen in the shell appe ars to be overabundant by a factor 10. The P Cygni profiles of N V and C IV are variable, possibly because of a suspected binary companion t o HD 50896.