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Eclipses No(s): 66
State: RisingAnother surprise from CG Draconis – a post-egress hump (PEH) during the very early rising stage of the outburst, combined with high orbital hump amplitude – a U/H/PEH type profile, seen first. There was an interruption in data right after the PEH peak, but we can still see it was rather narrow.
At this state the white dwarf’s accretion disk must still be dim and cold, or at least partially hot, as the bright spot is prominent, peaking at phase 0.85 when it’s directly facing Earth. Its amplitude almost reaches 0.2 mag, making it a “high” hump in my classification.
What normally follows is an asymmetric, slower egress, however, this time we have an opposite case, I think, caused by a PEH. peaking at approximately phase 1.1. This phase coincides with the emergence of the bright spot on the other side of the eclipse. This could signify that the diameter of the bright spot is bigger than the thickness of the accretion disk, or, perhaps, that the disk is unusually optically thin at this early stage of the outburst.
It would be really interesting to have some input on these speculations. Although I have only recorded two eclipses during the rising stage of the CG Dra outburst, I would expect asymmetric egress, with the bright spot concealed by the disk on the other side of the eclipse.
If the disk is so unusually transparent tonight, what suddenly caused it? We have seen no PEHs during previous eclipses after the bright outburst. If the bright spot is unusually large now, extending beyond the accretion disk, which is supported by the absence of the standstill on the egress, then does this signify an increased accretion rate? If so, what has suddenly caused it? We have seen that there was no PEH at all yesterday – the eclipse was asymmetric.
The more data is being collected, the more questions I have.
Max
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Yep, I’ll use question mark.
Eclipses No(s): 63, 64, 65 (next day)
State: Quiescence
Profiles: U/N/A, U/N/A, V/N/AAttachments:
Eclipses No(s): 61, 62
State: QuiescenceCG Dra can be very deceptive. Look at how different eclipse profiles are, separated by just 4 hours. Poor quality data, combined with flickering due to the bright spot on the accretion disk of the white dwarf makes the second eclipse appear almost symmetrical and much deeper than the first one. Wild flickering creates bumps in the orbital hump, sometimes right before the ingress (2nd eclipse). Random patterns due to the measurement uncertainty at the eclipse minimum (1st eclipse), then, removes or adds depth, and flickering at the egress (2nd eclipse) may occasionally play another joke. I think this is what is happening here. Two asymmetric eclipses with normal ~ 0.1 mag orbital hump (U/N/A), distorted by uncertainty and flickering, so they appear to be different.
A question: should I continue assigning eclipse types just as they appear on the light curve, like I did before, or should I compensate for these distortions due to poor quality data? There is more value in compensating, but if I do this, I’ll need to reclassify all poor-quality eclipses I’ve filed earlier (Whew…)
It would also be interesting to correlate FWHM with sigma. The night was pretty clear and dark. There was no extreme in temperatures. Why photometry quality suffered – I don’t know.
Max
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Eclipses No(s): 60
State: Quiescence
V/N/A. Intermittent clouds.Attachments:
Eclipses No(s): 59
State: QuiescenceCG Dra back to quiescent state with a typical U/N/A eclipse, normal ~ 0.1 mag orbital hump amplitude indicating a mix of accretion disk and bright spot components. Mediocre data quality due to the clouds. Roof was closed 9 times this night, so this was a good test of automatic telescope wake-up routines.
Max
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Eclipses No(s): 57, 58
State: Fading
A pair of U/N/A eclipses, normal orbital hump (albeit ~20% lower amplitude), asymmetric.Attachments:
Eclipses No(s): 55, 56
State: Fading
CG Dra is now fading after the bright outburst, reaching normal outburst luminosity. Two highly symmetric U/L/S-type eclipses signifying that the accretion disk is still bright, hot and ionized, concealing the bright spot.
MaxAttachments:
Eclipses No(s): 54
State: Bright outburst
U/L/S-type eclipse profile: U-shaped, low to none orbital hump, symmetric.Attachments:
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:
