Are all WCd stars binaries? An IGRINS search for companion stars

Some carbon-rich Wolf-Rayet stars are known to form dust (WCd stars). Several of these systems are now known to be binary stars where the shocked wind collisions provide the needed high densities and carbon-rich environments in which to form dust. However, we are not yet certain if all WCd stars are binaries or not, or if the dust can form in single WCd stars. We began a survey of known WCd binaries with the high-resolution IGRINS spectrograph in the near-infrared H and K bands. We report on the signatures of the massive O star companion in the WR 140 system as well as preliminary results on other WCd binaries as we begin to expand our survey to most known Galactic WCd stars with IGRINS at Gemini.