The results of a long-term monitoring program of the He II 4686-A and H-alpha emission lines of the massive X-ray binary Cygnus X-1 are presented. The radial velocities of the residual He II 4686-A emission profiles can be fitted to a smooth sinusoid with little scatter (+/- 10 km s^-1) with no significant eccentricity. There is no significant variation in the K amplitude estimated at different epochs which implies a stable origin for the emission. There is a phase lag of 134 degrees between the absorption and emission velocity curves. The results support the model published by Friend and Castor in 1982 in which the primary star almost fills its Roche lobe and has an enhanced mass flow toward the secondary. The He II 4686-A emission strength is strongly modulated (30%) with the 5.6-day orbital period. In 1982, the He II emission was significantly stronger than in other years. Such a change has been seen once before and may be associated with transition to the X-ray high state. The H-alpha profile appears to have three components: an underlying absorption from the primary, a shell emission, and an emission component with properties similar to the He II 4686-A emission line.
Department, Program, or Center
Chester F. Carlson Center for Imaging Science (COS)
Astrophysical Journal 321N1 (1987) 438-446
RIT – Main Campus