Long-term photometry of the Wolf-Rayet stars WR 137, WR 140, WR 148, and   WR 153
  In 1991, a long term UBV-photometry campaign of four Wolf-Rayet stars was started using the 60 cm telescope of the National Astronomical Observatory Rozhen, Bulgaria. Here we report on our observational results and discuss the light variations. The star WR 137 showed only random light variations, which are probably due to dynamical wind instabilities but not to eclipses. WR 140 featured a dip in the light curve, the amplitude increasing towards shorter wavelengths. The probable cause is electron and Rayleigh scattering when the star was eclipsed by a dust envelope. In the case of WR 148 we found a period of 4.3 days and significant scatter in the light curves. Additionally there seems to be a long term variation with a period of 4 years. Our photometry of WR 153 is consistent with the quadruple model for this star. 
Kyril P. Panov, Martin Altmann, and Wilhelm Seggewiss