This is a relatively low rank event, but bright, and anyway - how can you pass up an occultation by Mr.Spock? Alt=29, Az=132. In Aquila, just above the upper end of "the Teaspoon" formation of Sagittarius. Centerline through Pleasure Point, northern limit through Swanton Valley and Ben Lomond, but wider uncertainty. Odds of a "hit" are 56% from Santa Cruz, and 49% for Karl at home.
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Successful recording of the positive occultation from Kirk and I of the main event. Also, a secondary event is apparent in my own light curve, but no such event for Kirk's recording only 1 mile north of me. Interpretation is difficult as no explanations are natural and favored, and in fact all look quite unlikely. Can't easily write it off as noise, but a satellite interpretation also is problematic. We're left so far with only unlikely explanations.
Richard Nolthenius
I observed from the west side of Empire Grade at the entrance to Wilder Ranch at the bike crossing, upper meadow UCSC. Considitions were perfect - no clouds, warm, dry, I got good solid data. The strange thing was I also recorded a high S/N 4.7s event 29 seconds before the primary event. That's 20 asteroid diameters away from the primary event; rather far for it to be a satellite but not impossible. But if a satellite of reasonable shape, the 4.7s would be much larger than the main asteroid. 4.7s duration is 3x the max duration for the primary event! Yet it doesn't look like noise, and it passes the false positive test with high significance. Interesting too that it has a zero level at the center of the event. No neighboring stars show any dip, so clouds make no sense. But then, Kirk should have seen it too, as he was only about 1 mile from me, north. And his light curve shows no secondary event. A binary star likewise makes no sense, as the primary event was 2.2 mag deep, 87% loss of light (same for Kirk's recording) meaning it would have to be hitting the primary (brighter) of the putative binary star, leaving only a maximum 13% drop for the secondary event. But the secondary event was only 43% deep. Could some color difference combination with the band sensitivity of the Watec 910hx between primary and secondary stars still make this plausible? I don't see how. Perhaps a low density ring around this asteroid, nearly edge on so that I saw it with decent opacity, while Kirk at 1 mile north of me, did not have an occultation? We know how there are rings around Quaoar which are not at all consistent in their brightness in the azimuthal direction, and they are beyond the Roche Limit, and there's not just one ring around Quaoar, but two with these characteristics. Perhaps there was a moonlet small enough to cause a diffraction blurring to explain the shallower dip and help spread the event as well, further helped by the orbital vector of the moonlet so as to lengthen the duration of the event? I have no idea at this moment whether this is unphysical (i.e. violates the laws of optics or gravity).
OK, I'm going to keep these musings above here, on the page, because they're worth re-reading for future reference. I will say before you read further - this secondary event is most likely now to be atmosphere-caused. But I'll let this page read like a mystery story because it illustrates real-world thinking processes (And, because I don't want to erase it all!).
The relevant 1 min 20s which centers on the events, has been rendered as an .mp4 file and uploaded to YouTube. The 'secondary event' in the target star at 5:22:24 is very obvious. Not nearly so obvious is the dimming of the brighter star above/left of the target, 20 seconds later, at 5:22:42 for about 1.5 seconds, gradual fade/brighten. But, it's there if you replay it a few times.
My settings were: sharpness=4, gain=41, gamma=1.0, integration = 4x
PyMovie composite light curves of two reference stars, and (red) target star, with no-star (blue) |
The target star, with primary event in the middle, secondary event 29s earlier |
Light curve of one of the reference stars which was just 2 arcmin away from target |
Screen capture of my PyMovie screen, with target aperture below. Target star at normal brightness is shown, at end of recording period. |
Image of PyMovie screen at the time of the secondary event, also showing the two reference (= tracking as well) stars used. Both are only 2 arcmin from the target. |
PyOTE reduction for primary event showing 87% light loss |
Secondary event 29s earlier, with 43% light loss, lasts 4.7 seconds. Or 4.0 seconds if using the 'appsum' option in PyOTE See below for the most likely cause. |
Red bar test on main event, passes with strong significance. I trimmed the data to not include the secondary event, in PyOTE |
Red bar test on secondary event, passes with strong significance. I trimmed the data to not include the primary event. 4.7 second duration, but it still passes w/o this trimming. However, this test is only meant to show the event was not due to normal scintillation and read-out scatter noise, and may be a real occultation but it could also be a real signal drop for some atmospheric reason, of course. |
This is a 200 frame "finder" made in PyMovie, which includes the 4.7s secondary event, and ~3 seconds before it faded as well. |
More on the "finder" image above at far right. A 200 frame integration, and then background/range adjusted to show the background better. Dust on the sensor in the past has shown up as small slightly darker circles on images like this. I see none in this image. The vertical banding has been a "feature" of this camera ever since I got it. It is rather subtle and it disappears when I process in PyMovie using the "median vertical filter" option. This vertical banding has not had an observable effect on my light curves. The contrast above has been amplified by about a factor of 10 in the above image, so it looks worse than it is. And, the star remained centered between the darker columns seen on the video from well before to well after the secondary event. Also, I have played back the tape starting before and ending after the secondary event and the target star stays steady in a set of columns unaffected the dark banding you see here, and the 4.7s fading is easy to see. Could the banding affect sky subtraction even if not on the star? I have run PyOTE with 'signal' option and with 'appsum' option and the results are essentially identical visually. No visible evidence of a contrail or other cloud can be seen here. You'll see that brighter stars show a fainter star to lower right adjacent; this is I believe due to an artifact of the scope tracking during the 200 frame finder imaging.
I then tried using two reference stars which were more widely spaced (also set as tracking stars), to see if perhaps the tracking was first run's closer spaced ref stars made for poorer tracking of the target, as a possible problem. But it made no difference. The secondary event in the light curve still looks the same in this second PyMovie run, shown below
PyMOvie composite light curves; target in blue. |
Target star light curve. Secondary event is about ~900 frames before main event. and is quite obvious |
Reference star light curve. Nothing unusual seen here. |
I used the best choice of reference stars in my judgement. The next step... I used WeTransfer to send a copy of the .avi file to IOTA's Tony George so he could take a look at it. He thought of something I hadn't, which evolved out of his choice to add another, different, star to the aperture list... and shows a dip not too different than the 'secondary event' of the target star, and that changes the culprit search. Initially I had worried that that particular star might have saturated pixels sometime during the recording and so chose stars that were closer to the target in brightness, but no dimmer. The other problem was a mental block. I thought... "clouds"? There's none in the sky, none on the weather maps. It was a high-pressure dome dry warm night, and so cirrus and mid level clouds were off the table. And, our nemesis locally - fog - was also off the table. What I didn't add to the thought process was the possibility of contrails. Jet contrails can be thick and obvious, or they can be thin and short-lived, and they're high enough it's not obvious that the city lights would illuminate them. I have tried to pull any such contrail out of the dark sky in PyMovie here, but I still see nothing. I often sneak a look during recording to make sure there's no clouds, and also any jets flying nearby. I didn't note any, but they still could have been involved.
After getting Tony's work I re-analyzed my tape again, this time using every star I could put an aperture onto, and which would stay for the duration of the recording (the field drifted upward some, so stars near the top were tempting but unusuable). I had 2 tracking stars, the target, and 6 reference stars. Only the target star, and the bright star above it, clearly showed this 'secondary dip', although much shallower dips are seen during the recording, but which appear entirely normal for faint stars and wouldn't pass the redbar test. But one star's significant dip (ref-c) is enough. This secondary dip seen in Tony's analysis I see in mine as well, and it makes a case for an unseen jet contrail. The astronomical explanations are significantly less likely than the contrail theory. However, no contrail or cloud can be found on the images, is the still-nagging problem...
Field, with star labels. Note that "ref-c" star has a close companion which complicates using it as a comparison star (and might add noise to the aperture photometry here too? I don't think it would cause the kind of signal seen in the light curve, thougs. |
Ref-a star doesn't show significant dips, but it's faint and noisy |
Ref-c is the brightest of the chosen stars, and it does show a significant dip which might plausibly be due to a contrail remnant, is a decent guess. However, this star also shows a close companion which complicates using it as a reference star and why I didn't use it my earlier analyses. |
Reference star Ref-e, also faint and hard to judge, but the ? shows a possible dip from a contrail? |
Tracking star Track1, shows a dip late, and possibly others? It's closest to the target star. Dips are not clean and would not pass the red bar test |
Track2 tracking star, newly chosen |
And for comparison, the target star, with the genuine event at center, and the longer and likely atmospheric event 29 sec earlier |
Vadim Nikitin made an image from my raw .avi video that speaks to the so-far best hypothesis - a contrail.... He combined frames of my video by tracking along a path that would correspond to the "occulter" which we hypothesize dimmed both the target, and the neighbor star. The occulter would then be at the intersection of the two star trails; where the target and the brighter neighbor star touch each other. If it were a contrail, it could be oriented in any direction, but it would be consistent and burned into the image, and if it was a small cloud, it would burn in at that intersection of the two star trails. As you can see, there's just no evidence of an atmospheric occulter. You might be tempted by the vertical darkish band. That's almost certainly the two darkish columns already discussed - but you can look at the 'finder' and you can look at the video on YouTube and verify that those two darkish columns - one on each side of the target star, stayed on either side of the target during the entire secondary event, and so cannot be the cause. Again, even if one considered that maybe a flawed sky subtraction were the cause of the light curve dip, that could not explain the clearly visual occultation of the target seen live on the video, while the dark vertical bands still lay on either side of the target star but not touching it. |
IOTA report sent, containing only the primary main event, not the secondary, on July 23, 2023.
Kirk Bender
Kirk observed from the wide berm on Empire Grade a few miles north of my site. He too had excellent conditions. His light curve of the target star does not show a secondary event. Settings were: sharpness=4, gain=41, gamma=1.0, integration = 4x
Composite PyMovie light curves. Target is in blue, main event occultation is the sharp downspike in the middle. |
The target light curve in PyMovie. There is a hint of a dip in Kirk's light curve at a very similar place relative to the primary occultation, but it is only a hint. On its own, unremarkable. A contrail evidence too? We'll never know... |
PyOTE solution, zoomed in on the main event |
false positive test succeeded on the main event |
Target light curve is the bottom of the 3 light curves here, and vertical bar is on the moment at the center of the secondary event of my light curve secondary event, about 29s before the main event. |
