Reply To: CG Dra: a VSS campaign

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Maxim Usatov

Eclipses No(s): 51
State: Super-outburst

The previous long state of quiescence in the system has resulted in a super-outburst, with CG Dra now reaching 15.46 mag. It appears that all the material that has been flowing from the secondary was accumulating in the accretion disk and is now being dumped onto the white dwarf at a higher than usual rate.

The eclipse profile is V/L/PEH – V-shaped, low orbital hump and with a post-egress hump. Whether it’s a hump and not an isolated flickering event, is difficult to say, but I’m inclining towards the PEH scenario. This is the first V-shaped counterpart seen to PEH eclipses previously observed twice at and after normal outbursts.

The PEH shape is similar and appears to be at approximately the same phase as during the previous eclipses with this feature. I can only guess that this is the densest and the brightest part of the accretion disk, perhaps a bulge on it, or an overflow, appearing due to the increased activity and high viscosity of fully ionized material.

This is the highest quality data I have been able to record on CG Dra, with the standard deviation of the check star below 0.02 mag. The seeing tonight was exceptionally good, and I am glad I was able to fix some of the software issues to capture this data. The light curve is able to reveal the character of flickering, which likely originates in the accretion disk or the bright spot. There is no egress standstill which means that the spot is likely extended in size.

There is still some amount of bright spot hump visible in the ingress portion of the profile – it is slightly asymmetrical – which, probably, means that the bright spot is still contributing some considerable portion of the system’s light, despite it being in the super-outburst with hot, fully ionized accretion disk.