4 The nebular $\lambda5007~\rm [OIII]$ line

This line has been present throughout the whole investigated period with decreasing intensity (Fig. 4). Its profile was complex and dramatically variable in shape. Its multiple emission components of different velocities and profiles including a rectangular form at the beginning of 1989. support the idea that the [OIII] matter consists of several inhomogenous nebular clouds. The very improbable existence of a substantial accretion disc at this time rules out bipolar flows as ejection mechanism of this matter. It is most likely supplied by the cool component due to its mass loss by stellar wind. The nebula absorbs the ionizing radiation emitted by the hot component. The diminishing intensity suggests the decline of one or both mechanisms and the persistence of the mechanism which supports the shell- expansion away from the hot star.

  

Figure 4: Profiles of nebular $\lambda5007~\rm [OIII]$ line normalized to the continuum level at different epochs