The possible variability of emission lines in the circumstellar nebulae of WR and O stars on time scales of several years

Using a two-component model for the structure of the circumstellar nebulae of WR and O stars, we predict that their emission may be variable on time scales from several months to several years. This variability should be manifest as an enhancement of the emission luminosities of separate compact regions in the hydrogen Balmer lines, HeII ion line, and nebular lines of the ions OII], OIII], NeIII], and NeIV]. In the model considered, this line variability reflects non-stationary ionization, cooling, and recombination behind a shock propagating inward in the cloud. The set of lines that are variable depends on the shock velocity, while the scale of the variability decreases with increasing cloud density.