Reply To: CG Dra: a VSS campaign

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Maxim Usatov

Eclipses No(s): 40, 41
State: Quiescent

Another interesting situation. At first – very odd, where are the eclipses here? I see humps, but not dips. Data quality is not very good due to the moonlight and extreme heat, last nights are definitely not photometric, but the humps are real, as they are above the average 0.07 mag uncertainty.

So, I decided to let MetroPSF plot eclipse minima using last known AoV period – these are vertical green lines. Very odd – orbital humps generally appear to rise right before the dip, and here we see a very broad linear rise, then linear decline and no dip at all. I have double checked ephemeris calcualtion and green lines coincide with minima on the previously recorded night, so no error here. What’s going on?

I have decided to overlay today’s peculiar data set over previous quiescent nights in phase plot using Peranso – see attached. Looks like it is indeed a bright spot orbital hump, just much more pronounced one – an amplitude of 0.2 mag. The eclipse of the bright spot (or whatever it is!) is “delayed” by Δφ ≈ 0.05 compared to previous nights. Did the spot grow or, maybe, it’s not a spot at all, but something very bright and extended, maybe part of the accretion disk?

Orbital hump appears to contribute ~ 20% of the total system’s light with this amplitude. I guess accretion disk is very dim or small now. I have classified both eclipse profiles as U/H/HA type: U-shaped, High orbital hump, Highly asymmetric – a U-shaped counterpart of V/H/HA previously seen twice at quiescence and fading state of CG Dra.

Given poor quality data, it’s difficult to characterize flickering.