Spectroscopy of WC9 Wolf–Rayet stars: a search for companions

A spectroscopic search for luminous companions to WC9-type Wolf–Rayet stars making circumstellar dust reveals the presence of absorption lines attributable to companions in the blue spectra of WR 69 (HD 136488) and WR 104 (Ve2–45). Comparison of spectra of WR 104 observed in 1995 and 1997 showed the absorption lines to be more conspicuous in the latter observation and the emission lines weaker, suggesting a selective eclipse of the WC9 star similar to that observed by Crowther in 1996. The WC9 emission-line spectra are shown to be less uniform than previously thought, showing a significant range of O  ii line strengths. The only two WC9 stars in the observed sample that do not make circumstellar dust, WR 81 (He3–1316) and WR 92 (HD 157451), are found to have anomalously weak O  ii and strong He  ii lines. We suggest that these spectroscopic differences may reflect a compositional difference that plays a role in determining which of the WC9 stars make dust.