This is a bright event but a bit uncertain path, passing just north of MIRA Observatory. Alt=48, Az=186 in Ophiuchus. The rank is not great at 66. The error in time is listed at "0", but I take it that may mean "unknown but probably small". Could it be as large at 10s? Seems unlikely. In fact, clearly my big drop to zero at 10s after the event, correlated with strong wind dropouts on all ref stars too. The predicted southern limit was about 3 miles north of my site at the fire lookout, and about 3.3 miles north of Kirk at MIRA Observatory. We were both well inside the 1-sigma error limit.
The predicted duration was only 0.3 seconds, full drop. I should have set the integration to 4x, but changing location and fiddling with wind danger adjustments left me with too little time to experiment with other integrations than the 8x I still had on for the 2001VZ105 event an hour earlier. And, I was worried I needed longer integration to deal with the wind. Still, seems clearly a miss.
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Kirk got this one on the 14" Planewave at MIRA Observatory, while I set up behind my car as wind break at the fire lookout a mile north of the observatory. Both of our stations were a path width south of the path or thereabouts. I had a likelier position to see an event. The RUWE=1.05, which is under the 1.15 limit that defines "good astrometry", so perhaps the time uncertainty is not too bad. The fire lookout is 0.37 mi NW of the MIRA observatory.
I had done the first two occultations tonight in the lee of the personnel lightening cage at the base of the fire lookout. It was the widest wind break available, and did a decent job. But as the night wore on, the winds got stronger and began to shift a bit, and I also needed to keep moving to see this brighter target farther west and getting me deeper into the wind. I decided to move all my gear to the usual setup choice - directly out of the back of my RAV4 - as I thought this would provide a better wind break. I re-positioned my car to maximize wind break. Still, the wind was really a problem. As a final strategy, I had on my Montbell jacket and spread it out a'la Batman, during the actual recording, to provide maximum windshield. My integration setting was the same as for the fainter 2nd event; 8x.
For reductions, I chose the 'dynamic mask' as the far superior choice to deal with the irregular wind shear effect on the stellar images. The target at R=11.8 was bright enough to get nicely above zero for the large majority of integrations. There was a distinct loss of light for a full 2 seconds at 9:52:40 UT. This duration is much too long to be due to an occultation, and is 10s after the predicted event time, and must be due to wind caused loss. In fact, you see it affected the reference stars at the same moment.
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I adjusted background/range to maximize visibility of the target during the reduction, so as to follow along best. I do this on all occultations. |
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Histogram clipping on background sky was significant. The "zero level" for sky and therefore for this 5+ magnitude predicted drop event, was not at 0 but at level=27. |
Level=27 would be proper occultation depth. In fact, the moment of predicted occultation was a noise-spike upward. Clearly this was a "miss". |
Kirk observed on the 14" Planewave scope under the 36" main MIRA telescope. He was well protected from the wind, and the scope geometry is open-truss and further advantaged in the wind. Still, bad seeing would benefit from "dynamic mask" analysis. But testing on the first event of the evening showed the advantage was small, and the data quality high enough to justify the conclusion this was a mis, as my own observations confirm. He used 4x as integration setting.
Here are plots for the third MIRA event, 1981 EO10, 4x, static circular in pymovie, with block integration and smoothing in pyote, vertical line at predicted event time for MIRA.
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