Reply To: CG Dra: a VSS campaign

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Maxim Usatov

Eclipses No(s): 25, 26
State: Quiescent
Data Quality: Good (check star sigma = 0.041)

CG Dra keeps surprising. We see a pair of eclipses, on a single night, with quite different profiles. The time between the eclipses is about 4 hours, so the system is so active that significant changes can be observed in such a short period of time.

Eclipses are of type U/N/A (first) and V/N/A (second), which is typical for CG Dra. The minima appear to be V-shaped in the former, and U-shaped in the latter eclipse. I guess the shape appears different due to the flickering and chance alignment of measurement points, the orbital alignment of both events should be similar. Flickering amplitude appears to be 0.5 to 1 mag. I think the shape difference can be ignored, but look at the slope of the ingress curves!

There is now a dashed red line that shows the light curve smoothed with the Gaussian filter. Although I didn’t get the early phase of the bright spot appearance in the first eclipse, it should be similar to that of the second, at 16.86 mag. The first bright spot peaks at 16.77 mag and has the amplitude of 0.09 mag. The second bright spot peaks at 16.78, so the amplitude is 0.08 mag. So as both spots have about the same amplitude, why the ingress curve in the second eclipse is steeper, and why the eclipse itself is deeper? The minimum of the first eclipse is at 16.94 mag, while the second is 16.98 mag. My guess it is again due to the flickering.

Note, also, ~ 0.08 mag temporary brightening on the egress of the first eclipse, with gradual return to the normal curve, although this time there is no plateau like yesterday. Similar temporary brightening event is observed later between the eclipses.

There is a smooth brightening curve in the middle-left portion of the chart after the first egress. I wonder if this is the relection effect from the red dwarf.

There appears to be a standstill on the egress of the second eclipse. This corresponds to a compact bright spot according to Cook & Warner (1984), although again I could be imagining things due to the high amount of flickering present.