Longperiod Optical Variability of the CYGNUS-X-1 System Kemp, J. C. ; Karitskaya, E. A. ; Kumsiashvili, M. I. ; Lyutyi, V. M. ; Khruzina, T. S. ; Cherepashchuk, A. M. Abstract Publication: Soviet Astronomy Pub Date: April 1987 Bibcode: 1987SvA....31..170K