Optical Studies of UHURU Sources. VII. Photoelectric Photometry of HD 77581 = 2u 0900-40

Photoelectric UBV observations of RD 77581, the sixth magnitude BO I star associated with 2U 0900-40, show that the star's brightness goes through a double cycle during the 8.95-day binary period found from X-ray observations. Our observations show that the cycles do not repeat exactly and that there is little change in color. Subject headings: binaries - variable stars - X-ray sources