DL Cyg
Bradstreet2004 - Bradstreet2004R (Johnson R)
This is just a rudimentary attempt at modeling this interesting system, showing that a small dark spot on the primary star located 30 degrees off the line of centers of the two stars can fairly well approximate the effects of a changing opacity gas stream coming from the secondary star through the L1 point and flowing to the primary star. The limitations of this approximation are that a spot is a crude approximation for the obscuring nature of a gas stream. One can conceive of the opacity of the gas stream increasing as primary eclipse approaches and the observer’s line of sight through the gas stream steadily passes through a denser cross-section of the stream. Thus more and more light of the primary star would be blocked right up until first contact when the stream is also eclipsed. Likewise, on the other side of primary eclipse, the line of sight through the gas stream would not block the primary, and hence the effects of its opacity would not be observable. This is not the case with this simple spot model, where the dimming effects of the cool spot are still seen just after eclipse (i.e., the model doesn’t fit just after the ascending branch) and hence the shoulder is a bit beneath the brightness level that it should be.