Multi-colour photometric and spectroscopic monitoring of the WN5 star EZ Canis Majoris ^*

¹ Leiden Observatory, Postbus 9513, NL-2300 RA Leiden, The Netherlands
² Space Research Organisation Netherlands, Sorbonnelaan 2, NL-3584 CA Utrecht, The Netherlands
³ Nordic Optical Telescope, Apartado 474, E-38700 Sta. Cruz de La Palma, Canarias, Spain
⁴ Kapteyn Laboratory, Postbus 800, 9700 AV Groningen, The Netherlands

Send offprint request to: A.M. van Genderen

Received: 6 December 1995
Accepted: 21 February 1996

Abstract

We present and analyse photometric and spectroscopic observations of the WN5 star EZ Canis Majoris obtained over a period of 7 years. We discuss the changing light curve, the shift in phase of the maxima and point to flare type variability seen in one night. Small amplitude variations are reported in another night. We have investigated the change of 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) with a range of . This, of course, should be verified. If true, a precession phenomenon may offer an explanation. The trend of the maximum light amplitude of the cycle is also investigated and it shows a saw-tooth character with a timescale of . A possible relation with the magnetic activity of the star is discussed. 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.