Bright event. But RUWE =1.65 which is not great for the star position, so path not as high rank as it looks on OWc. Karl's well positioned. I'm closing up at Cabrillo Observatory or maybe I'll turn people loose early so I can get above the fog??
Alt=59, Az=110 in Pegasus, 45 deg from the gibbous moon
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We had clear skies and were getting great photos from our new modern cameras, so no leaving early. I stayed late, and decided I'd guard the southern limit while Karl guarded the north, and Kirk wasn't far north of me. It was better spacing for better science. And, I got lucky and the path did shift south so I had a solid event.
I got two recordings, both from the same Watec 910hx PAL I normally use. One output went to the ZR45mc camcorder, and the other to the Startech and Lenovo computer. The goal was to see how the S/N's compared for these two different methods. I observed at 2x from outside the dome building at Cabrillo Observatory, under clear skies with some moonlight but not near the target. I got a positive, 2 seconds early. Was this due to the high RUWE of the target star? I applied median filtering in horizontal and vertical directions.
First reduction is for the Lenovo recording...
start: 5:27:01 UT
End: 5:30:38 UT
NIE test; 32.1 sigma
magDrop report: percentDrop: 91.5 magDrop: 2.679 +/- 0.518 (0.95 ci)
DNR: 2.97
D time: [05:28:23.5187]
D: 0.6800 containment intervals: {+/- 0.0100} seconds
D: 0.9500 containment intervals: {+/- 0.0268} seconds
D: 0.9973 containment intervals: {+/- 0.0640} seconds
R time: [05:28:24.5987]
R: 0.6800 containment intervals: {+/- 0.0100} seconds
R: 0.9500 containment intervals: {+/- 0.0268} seconds
R: 0.9973 containment intervals: {+/- 0.0640} seconds
Duration (R - D): 1.0800 seconds
Duration: 0.6800 containment intervals: {+/- 0.0146} seconds
Duration: 0.9500 containment intervals: {+/- 0.0341} seconds
Duration: 0.9973 containment intervals: {+/- 0.0715} seconds
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Clear occultation 2s early for the target. |
Ref2 had a surprising drop to only 61% of normal brightness for 2.5 seconds, about a minute after the target occultation. |
Here it is close up. What caused this?? |
In PyOTE, solution was sharp and high confidence |
Zoomed in. Occasional pixels on the target were red and near or past saturation at 2x. |
NIE test; 32.1 sigma |
The puzzle is what caused the drop in brightness of the ref2 star? It lasted a full 2.5 seconds and dropped to 61% of normal brightness. There were no clouds, and ref1 and the target did not show a drop at this time. A bat? An owl? But for 2.5s that is not plausible - these animals do not hover, they are fast movers, and would occult a star for less than 0.1seconds, and would also show on other stars. I recorded this event also on my ZR45mc camcorder and the light curves are as good or better than the Lenovo / Startech IOTA VC 2.4 recording. I do not see any other star on the field which did anything unusual at or near the event of the ref2 star...
2nd Reduction, using the output into the ZR45mc camcorderd
Reference star numbers used for the camcorder recording reductions |
Screen capture on PyMovie. I used 2.4px fixed circular masks on all stars. |
Composite of all light curves. |
Target star, with a clear occultation at the proper time. |
Ref1, shows no unusual behavior at the time of the ref2 star's apparent occultation. |
Ref2 and the clear event |
zoomed in, the event looks more like a gradual fade, levelling off, then rising gradually |
Ref3, shows no unusual behavior |
Ref4, shows no unusual behavior |
Ref6, shows no unusual behavior |
Ref7, shows no unusual behavior. This is the star closest to ref2, and is the best evidence against a local occulting object like a bird or plane. |
Ref8, shows no unusual behavior |
Ref9, shows no unusual behavior |
Ref10, shows no unusual behavior, although it is very faint and shows many drops to zero. It also has a close fainter neighbor which would complicate interpretting the light curve. Not a good test. |
Ref10, zoomed in. The noisy lower values are hard to judge, later than the ref2 clear event. |
I got an obvious 1.1678s event for 1998 UC45, 1x from home on Sep. 29, time and duration as predicted.
PyOTE NIE sigma distance = 17.6
magDrop report: percentDrop: 89.0 magDrop: 2.392 +/- 0.770 (0.95 ci)
DNR: 1.66
D time: [05:28:24.4909]
D: 0.6800 containment intervals: {+/- 0.0118} seconds
D: 0.9500 containment intervals: {+/- 0.0455} seconds
D: 0.9973 containment intervals: {+/- 0.0978} seconds
R time: [05:28:25.6587]
R: 0.6800 containment intervals: {+/- 0.0118} seconds
R: 0.9500 containment intervals: {+/- 0.0455} seconds
R: 0.9973 containment intervals: {+/- 0.0978} seconds
Duration (R - D): 1.1678 seconds
Duration: 0.6800 containment intervals: {+/- 0.0190} seconds
Duration: 0.9500 containment intervals: {+/- 0.0547} seconds
Duration: 0.9973 containment intervals: {+/- 0.1165} seconds
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(Was median filtering applied?)
DNR: 3.11
D: 0.9973 containment intervals: {+/- 0.0679} seconds
R: 0.9973 containment intervals: {+/- 0.0679} seconds
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Kirk and Karl both ended their recordings before this event, so can't shed light on it. I'm still seeking to know when Kent Okasaki's recording ended. His chord was very close to Karl's, on the north side and not close to my chord. Still, for a 2.5s event, it may have been recorded by him as well.
Sources we can rule out:
1. A power glitch - no other stars showed strange behavior around the ref2 event time
2. An overhead power line? No, there are no overhead power lines at the Observatory
3. A bat or owl? No - while their wing span is capable, they move far too fast to hang over the telescope for 2.5 seconds+
4. a bump of the tripod or gear? No - no other stars show unusual events at that time
5. An orbiting satellite - No, NEO satellites move vastly too fast to cause a 2.5s occultation. A Geosynchronous satellite would be sunlit and that too would occult too fast to account for a 2.5s event.
6. A cloud? No - there were not clouds on this dry calm high-pressure dominated day. None seen by any of this team around the sky. Still, a thin small cloud in principle could be there, but how would it avoid all the other stars nearby? Some sort of emission by an airplane? But airplanes have lights and would have been seen on the video. The video when played at normal speed shows the star fading and then re-brightening with no other lights or visible traces on the video. No reflections from gound lights off a bird or drone.
Not yet ruled out entirely:
* a weather balloon? It would have to be very tiny, well less than an arc minute across and thread between the other stars, most importantly ref7, which was less than 1 arcmin from ref2. A weather balloon 30 ft across would have to be 30 miles high to subtend 30" and stay motionless for 2.5s. If rising, it would have to be rather larger and also not occult ref7 which was right vertically above the ref2 star. Still, I will try to find out if any weather balloon's were launched.
* a drone? A typical ~1 ft across consumer drone would perhaps occult enough light to work, but to avoid all other stars, the drone would have to be less than 30" angular diameter. That corresponds to a distance from the telescope of 1.3 miles and at the altitude of the target of 59 degrees, corresponds to about 1.0 mile above ground. Why would a consumer drone be that high? And how could it stay absolutely motionless for 2.5s despite higher wind speeds at that altitude?
