MULTICOLOR PHOTOMETRIC AND SPECTROSCOPIC MONITORING OF THE WN5 STAR EZ CANIS-MAJORIS

We present and analyse photometric and spectroscopic observations of t he WN5 star EZ Canis Majoris obtained over a period of 7 years. We dis cuss the changing light curve, the shift in phase of the maxima and po int to flare type variability seen in one night. Small amplitude varia tions are reported in another night. We have investigated the change o f the average visual magnitude over a time span of 18 years and found a tentative cyclic variation with a time scale of 2425(d) (6.6 yr) wit h a range of similar to 0.(m)07. This, of course, should be verified. If true, a precession phenomenon may offer an explanation. The trend o f the maximum light amplitude of the 3.(d)766 cycle is also investigat ed and it shows a saw-tooth character with a timescale of similar to 4 00(d). A possible relation with the magnetic activity of the star is d iscussed. We conclude that the line emission variability can be caused by both a single star model with an ever-changing wind and a binary ( WN+NS) model.