2009ApJ...698.1951S

We present the results of a systematic search for large-scale spectroscopic variability in apparently single Wolf-Rayet (WR) stars brighter than v ∼ 12.5. In this first paper we characterize the various forms of variability detected and distinguish several separate groups. For each star in our sample, we obtained 4-5 high-resolution spectra with signal-to-noise ratio ∼100. Our ultimate goal is to identify new candidates presenting variability that potentially comes from corotating interaction regions (CIRs). Out of a sample of 25 stars, 10 were found to display large-scale changes of which four are of CIR-type (WR 1, WR 115, WR 120, and WR 134). The star WR 134 was already known to show such changes from previous studies. Three WN8 stars present a different type of large-scale variability and we believe deserve a group of their own. Also, all three WC9d stars in our sample present large-scale variability, but it remains to be checked if these are binaries, as many dust-making WR stars are double. Finally, of the remaining stars, 10 were found to show small-amplitude spectral changes, which we attribute to normal line-profile variability due to inhomogeneities in the wind, and five were found to show no spectral variability, as far as can be concluded from the data in hand. Follow-up studies are required to identify potential periods for our candidates showing CIR-type changes and eventually estimate a rotation rate for these WR stars.