Nine WC 9 stars spectral variability

We searched for periodicities in integrated line quantities for CIII {lambda}5696. Radial velocity changes are typically ~20km/s but never exceed 40km/s and are anticorrelated with the skewness of the line, strongly suggesting that they do not correspond to a real movement of the star. No periodicity was found in these integrated quantities, except for WR 103.

Therefore, a wind-wind collision in a close binary does not seem to be responsible for the short-term variability. We cannot, however, exclude that these stars are intermediate- to long-period binaries. We estimate that for periods up to a few years, the shock-cone resulting from wind collisions would be non-adiabatic and thus unstable.

We suggest that this represents a viable mechanism to explain the spectroscopic variability.