Abstract
Searching for spectral variations similar to those observed in the WR binary HD 5980 in the Small Magellanic Cloud, the authors have re-observed the WN+O binary systems WR 21, WR 31 and WR 47 at CASLEO, San Juan, Argentina. Compared with previous observations, the spectral morphology of these binaries does not appear to have changed. From the new radial velocity data of emission lines in the WN spectra, improved periods are determined for all three binaries. The authors also report the peculiar behaviour of the N IV 4058 Å emission line in the spectra of WR 21 and WR 47. In the new data, this emission follows the orbital motion of the WN component, but with a mean velocity shifted to more negative values when compared with previous data. This may indicate an enhanced expansion in the atmosphere of the WN component.
