Hi Robin,
That’s a very convincing B-V curve – so the photometric and spectroscopic eclipse mid-points are in good agreement, like they were also in the two studies I cited in my paper from the late 1997-98 eclipse. Could some variability in the red supergiant be a factor in the changes in the eclipse measurements? It’s hard to understand and makes the next eclipse in 2038 an event to be anticipated!
Cheers
Hugh