CG Dra: a VSS campaign

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  • #611206
    Maxim Usatov
    Participant

    Eclipses No(s): 33
    State: Fading
    Data Quality: Very good (check star sigma = 0.023)

    Another surprise from CG Dra. Of course, the meridian flip had to occur on minima (double-checked with Peranso). Here we see no ingress hump, but post-egress hump of ~ 0.1 mag amplitude – haven’t seen this before. Is this part of an asymmetrical accretion disk outshining the flickering source?

    We also see wild pre-ingress and post-egress flickering of up to 0.14 mag – nothing signifying we shouldn’t trust this data. Post-egress standstill.

    This curve had me to introduce another type of eclipse profile observed. I’ve catalogued it as ?/L/PEH (unknown shape, low orbital hump amplitude, post-egress hump).

    Max

    Attachments:
    #611211
    Maxim Usatov
    Participant

    Eclipses No(s): 34
    State: Fading

    V/N?/A eclipse (ingress hump not captured fully). Accretion disk is fading, post-egress standstill signifies compact bright spot. Normal flickering throughout the curve.

    Max

    • This reply was modified 1 month, 1 week ago by Maxim Usatov.
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    #611220
    Maxim Usatov
    Participant

    My location is all clouded for a week. It would be great if somebody could do a few points so we could time the end of this outburst. This would allow to estimate the distance of the CG Dra’s bright spot for this outburst cycle.

    Max

    #611236
    Maxim Usatov
    Participant

    Was able to make a few points from Mayhill, NM yesterday and time the return to quiescence. Using rearranged equation from Osaki (1974), I have estimated the distance of the bright spot, r_spot, from the primary star – see attached.

    Eclipse 24 starts after the previous outburst, so the r_spot decreases during the quiescence. Then, the star luminosity begins to rise, however, r_spot remains at ~12-13 white dwarf radii. The bright spot distance begins to increase up to 26 WD radii when the system is already approximately a day at near-peak outburst luminosity, and then begins to decline as the star begins to fade. So, this shows r_spot change follows the change in the luminosity. With U Gem, according to a chart in Hellier’s book (p. 59), U Gem’s disk begins to increase at the onset of the outburst and reaches peak size at ~ 10 days after the outburst. Disk expanding during the outburst, however, not before, is expected.

    Max

    #611238
    Maxim Usatov
    Participant

    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

    #611372
    Maxim Usatov
    Participant

    Eclipses No(s): 35,36
    State: Rising

    Continuing 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

    Attachments:
    #611374
    Maxim Usatov
    Participant

    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.

    #611376
    Maxim Usatov
    Participant

    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

    • This reply was modified 4 weeks, 1 day ago by Maxim Usatov.
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    #611421
    Maxim Usatov
    Participant

    Eclipses No(s): 38, 39
    State: Fading
    V/L/S + U/L/S eclipses. Bright accretion disk while the system is approaching quiescence.
    Max

    Attachments:
    #611469
    Maxim Usatov
    Participant

    Eclipses No(s): 40, 41
    State: Quiescent

    Another 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

    • This reply was modified 3 weeks, 2 days ago by Maxim Usatov.
    #611474
    Jeremy Shears
    Participant

    Looks like you are extracting lots of interesting details and features out of your data, Max. Great to see!

    #611484
    Maxim Usatov
    Participant

    Thanks, Jeremy!

    Eclipses No(s): 42, 43
    State: Quiescent
    ? + U/N/A eclipse, typical for this state.

    Attachments:
    #611488
    Maxim Usatov
    Participant

    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.
    Max

    Attachments:
    #611497
    Maxim Usatov
    Participant

    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.
    Max

    Attachments:
    #611499
    Jeremy Shears
    Participant

    Thanks for the heads up on an imminent outburst Max!

    #611506
    Maxim Usatov
    Participant

    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:
    #611508
    Paul Leyland
    Participant

    Please keep up observing and the pattern matching.

    It seems very likely to me that outbursts are somewhat predictable, it is just that we don’t yet know how to predict them with much reliability.

    #611510
    Maxim Usatov
    Participant

    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

    Attachments:
    #611512
    Maxim Usatov
    Participant

    Eclipse No(s): 49
    State: Quiescent

    Nope, I was wrong. It’s still quiescent. Tonight’s data – V/N/A eclipse, light curve without trend.

    Attachments:
    #611534
    Maxim Usatov
    Participant

    Eclipse No(s): 50
    State: Quiescent

    Some 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

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