THE ORIGIN OF EXTENDED INTERSTELLAR SHELLS AROUND WOLF-RAYET STARS HAVING BRIGHT OPTICAL RING NEBULAE

Investigations of the interstellar environment around Wolf-Rayet (WR) stars have led to the discovery of extended shells of gas and dust 50- 100 pc in diameter in the lines of sight toward three WR stars. In thi s paper, several origins for these extended shells are discussed. Whil e positional coincidences cannot be excluded; the locations of the WR stars near the projected centers of the shells, the detection of only shortward-shifted, high-velocity UV absorption line components in thei r IUE spectra, plus commonality of some WR star properties which are r are in the general WR star population suggest some causal connections between the WR stars and formation of interstellar shells. To access w hether the high-velocity UV interstellar absorption lines are a freque nt phenomenon related to WR stellar winds, we present a survey of such features in all WR stars observed with IUE through 1991. Of 35 stars studied, only four are found to have components with velocity displace ments greater than 45 km s(-1) which are not attributable to previousl y identified OB association superbubbles. This means a surprising 82% of non-OB association WR stars show no evidence of high-velocity gas i n their lines of sight at IUE's spectral resolution, suggesting that h igh-velocity interstellar absorption lines are not a common consequenc e of Wolf-Rayet star stellar winds alone. We review the properties of three WR stars (HD 50896, HD 96548, and HD 192163) which may reside in side extended interstellar shells and find that they are similar in te rms of spectral class (WN5-8), presence of an optical ring nebula, and reported photometric variability. Evaluation of possible origins of t he extended shells suggests these three stars are in a post X-ray bina ry stage of high-mass binary star evolution. If this is correct, then the large interstellar shells detected might be evidence of either sup ernova remnant shells generated by the explosion of the binary's prima ry star, or non-conservative mass transfer during a Roche Lobe overflo w stage of the binary after the supernova explosion. In either of thes e cases the bright optical ring nebulae associated with these three WR stars may signify recent Roche Lobe overflows consistent with spectro scopic abundance analyses.