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Eclipses No(s): 52, 53
State: Bright outburstAs per discussion with Jeremy Shears, I am now calling this CG Dra state a “bright outburst,” to avoid confusion with SU UMa superoutbursts.
Post-egress humps (PEH) amplitude appears to have decreased significantly to barely noticeable in the light curve (more pronounced in the phase plot), so I am filing these as U/L/S and V/L/S eclipses with low (or no) orbital hump and symmetric profiles. It’s actually difficult to say what qualifies as a symmetric profile, as we still can observe a gentler egress in both eclipses. Nevertheless, given that the egress magnitude is approximately equal to the ingress, ignoring very mild PEH, I think we can call this a symmetric profile.
Interesting dips in the curve. We can observe normal ~ 0.1 mag flickering throughout the curve except the minima, however, there is also 0.15 mag dip near the center of the chart, followed by a flat top. Note that flickering decreases down to ~ 0.05 mag at both minima. This may mean that high-amplitude and slow flickering events originate in the bright spot, while low-amplitude and fast flickering originates in the uneclipsed parts of the accretion disk.
Max
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Sorry, always have something to say after the “Edit” button disappears..
What if CG Dra disk is becoming elongated, responsible for the PEHs during or near some of the high-mass transfer outbursts, but then, as its radius changes, becomes circular again, so it does not precess at all? This would explain why PEHs do not appear in quiescence and that there is no beating period. What I am thinking of is a borderline U Gem/SU UMa case with weak temporary resonance events, whereby superhumps are invisible in quiescence and appear only occasionally during the outbursts. Of all outburst peaks, profiles without PEHs were seen 5 times so far, and 2 with PEHs, so roughly half to a third of the time we see those humps at outburst peaks.
But I really like the “partial AD outburst” idea.
Max
Here is the eclipse width. Red is the current bright outburst, black are the previous three outbursts. I didn’t align them vertically, that’s why they appear as a band. The current outburst profile does not appear to be wider than the previous ones. (Ignore the phase axis, as I haven’t set the epoch.)
Max
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Thanks. I haven’t measured the period, as these PEHs only appear occasionally. This is the third time I am seeing such a hump.
Totally makes sense. Are superhumps a pre-requisite for an outburst to be called a “superoutburst”?
Wild idea… Could CG Dra be an intermediate between U Gem and SU UMa with q ~ 0.3, spending most of the time with a circular disk but sometimes having an elliptical disk. Would a post-egress hump observed qualify for a “weak superhump”?
Eclipses No(s): 51
State: Super-outburstThe 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.
Max
Thanks, Jeremy. It just went into outburst at 15.85 mag, but due to the software issues in the observatory I was only able to obtain 5 measurements tonight.
MaxEclipse No(s): 50
State: QuiescentSome limited data tonight – only 123 observations – still struggling with random ACP crashes in the observatory. I believe it’s a hardware issue so might take some time to find the culprit.
Appears to be a typical U/N/A eclipse. What is odd is that CG Dra is quiescent for too many days in a row – I would have expected an outburst by now.
Max
Eclipse No(s): 49
State: QuiescentNope, I was wrong. It’s still quiescent. Tonight’s data – V/N/A eclipse, light curve without trend.
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Actually, it could have started an outburst yesterday. Now plotting a trend line. If this is true, we should definitely see it in outburst today. Today’s data is still processed by the pipeline. Here’s the chart with the -0.26 mag/d trend. I’ll refile it as rising eclipses.
Max
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Eclipse No(s): 47, 48
State: Quiescent
U/N/A + U/N/A. Looks like high orbital hump doesn’t always lead to an outburst. It just subsided to normal amplitude.Attachments:
Eclipse No(s): 45, 46
State: Quiescent
U/H/A? + U/H/A eclipses. High-amplitude orbital hump, looks like it’s going to go into outburst soon.
MaxAttachments:
Eclipse No(s): 44
State: Quiescent
Initially thought it has symmetric profile, but I really think it’s asymmetric, hidden in uncertainties. So, U/N/A. The weather is still not ideal, and I think more high-quality data would be needed to introduce a new type of eclipse profile (U-shaped, normal orbital hump amplitude, symmetric – U/N/S) into the system.
MaxAttachments:
Thanks, Jeremy!
Eclipses No(s): 42, 43
State: Quiescent
? + U/N/A eclipse, typical for this state.Attachments:
Eclipses No(s): 40, 41
State: QuiescentAnother 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.
Max
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Eclipses No(s): 38, 39
State: Fading
V/L/S + U/L/S eclipses. Bright accretion disk while the system is approaching quiescence.
MaxAttachments:
Eclipses No(s): 37
State: Outburst (Peak)Appears to be another U/L/PEH eclipse – U-shaped, low to none bright spot orbital hump, post-egress hump (PEH). The last one was seen while CG Dra was fading, this one is at the outburst peak. Another option is that it could be a symmetric U/L/S eclipse, but the accretion disk is just getting brighter. (Although this wouldn’t explain why PEH appeared on the June 30th eclipse while CG Dra was fading.)
The PEH appears to appear right after the egress of the accretion disk. I am not sure how to interpret this – asymmetric accretion disk or the appearance of an accretion stream/overflow? I wonder if magnetic forces are in play here.
Looks like flickering originates in the accretion disk or stream, as it is present even during the eclipse. Data quality is pretty good this night, and we can clearly see the flickering magnitude is above the average measurement uncertainty at the bottom of the “U.” There is no standstill on the egress, and this could signify large bright spot reaching the inner portions of the accretion disk. As we suspect CG Dra shows us grazing eclipses this configuration may explain the persistence of flickering throughout the eclipse.
Max
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Update: I think eclipses are U/N/A, and not U/L/S. I got confused by the steep rise in magnitude in this curve. If the base of the eclipse is visually extended past the egress, they are really asymmetric.
Eclipses No(s): 35,36
State: RisingContinuing after a cloudy break in the observatory, a pair of U/L/S-type eclipses, with light dominated by the bright accretion disk. Difficult to measure bright spot amplitude, as it appears there are spikes and dips in the light curve when it rotates into view, instead of just normal orbital hump.
There is some standstill on the ingress of both eclipses, although could be a flickering fluke.
Max
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Sorry, always have something more to say after I hit the “Send” button (and there’s no “Edit” anymore for some reason). I was inaccurate with the r_spot change statement. Looks like the drop in r_spot and an increase of the bright spot light contribution fraction could be a potential indicator of the upcoming outburst.
Max
