A UNIQUE PERIOD FOR THE WN5 STAR EZ CMA

We have obtained three months (mid Feb.-mid May 1993) of uninterrupted, precision, narrowband visual, continuum photometry of EZ CMa which allows a viable search for periodicities at unprecendented high resolution in the frequency domain. We find only one independent significant period, P = 3.76d, as first claimed in 1980. The phased light curve shows complex structure (3 sub peaks) but a high level of coherency during the first approximately 8 weeks. A sudden change leads to a different, but still coherent, light curve during the last approximately 4 weeks. Since only one period persists, it must have its origin either in rotation as a single WR star (e.g., oblique rotator) or in a binary (e.g., with a compact companion).