Blogs / Dr.Bob's blog / Where's my totality, dude?
Where's my totality, dude?
Predictions suggested the total eclipse phase of epsilon Aurigae should have arrived as early as mid-December [JD 2,455,190], but observers are still reporting a slow fade even now in late January [JD 2,455,220]! What's going on?
The answer includes the notorious "out of eclipse" variations -OOE- which are still lurking in the eclipse light curve. These have amplitude of one-tenth magnitude (or more) and a quasi period of two or more months. By using a 5 to 10 day mean in plotting the visual light curve data, you can see evidence for at least one local maximum around JD 2,455,160. The excursion from a straight line during ingress is only ~0.05 mag, but it takes only a small size variation or an even smaller temperature variation in the F star to cause that kind of variation.
It is still possible that these OOE arise from a hot source near the center of the dark disk, but finding evidence for/against this may be possible during this summer's mid-eclipse interval.
In any event, because of the fine coverage that you and other photometric observers have been providing, we are well positioned to deconvolve the time of second contact, start of totality, but after the fact, when the OOE can be fully taken into account. The current slow fade seems consistent with a declining phase of OOE since JD 2,455,200 or so, meaning that Feb may show a slow brightening at the limit of visual estimate precision. This again is why DSLR and photometric efforts can help better define these small amplitude excursions, so key to interpreting this fascinating star system, and many others. Check out the Citizen Sky and AAVSO tutorials on those topics. Thanks for your help!
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