Investigation of blue-sensitive photographs of HDE 226868 = Cygnus X-1 reveal no (+ or - 0.06 mag) long-term changes in brightness since the beginning of the century nor any abrupt intensity changes similar to what was observed at X-ray and radio frequencies. From the double sinusoidal fluctuation with 5.6 day period, an attempt is made to derive a more precise value for the orbital period, but problems are encountered and discussed. There exists evidence that the amplitude of the orbital fluctuations is increasing slowly with time.
The long term variability of HDE 226868 = Cygnus X-1
1976-01-01
Conference paper
No indication
English
Cygnus X-1 from RXTE: Monitoring the Short Term Variability
British Library Conference Proceedings | 2001
|Cygnus X-1 from RXTE: monitoring the short term variability
Online Contents | 2001
|The time variability of Cygnus X-1
NTRS | 1976
|The Long-Term Hard X-Ray Behavior of Cygnus X-1
NTRS | 1994
|