Reply To: CG Dra: a VSS campaign

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Maxim Usatov

Eclipses No(s): 87
State: Fading

Surprising curve today on the way down – broad U-shaped profile, highly asymmetric, no orbital hump. Very extended post-egress brightening all the way from phase ~ 1.15 to 1.50 – almost as if the bright spot is on the wrong side of the eclipse. Assuming this can be called a post-egress hump, except that it is a very broad one, this curve can probably be classified as U/L/PEH. We have seen this profile during the fade on June 30th except that back then the PEH was much narrower.

What causes such variation of minima shapes – this “U” is extremely broad – bright and very extended accretion disk?

Wild speculation, again, on the magnetic theme. Can CG Dra’s WD magnetic field switch on and off, sometimes turning the system to something resembling a polar? The patchy stream of material can block the bright spot at phase ~ 0.8, resulting in lower ingress flux, compared to egress. This U/L/PEH curve is somewhat similar to HU Aqr and SDSS J093537.46+161950.8 which Hardy et al. (2017) describe as a “typical polar.”

Seeing overall was very good tonight – there are interesting flickering oscillations towards the end of the curve. Note some fast flickering episodes reach close to 0.2 mag in amplitude.