This event passes through Santa Cruz with good rank. But tough; only a 0.3 dip and a close confounding neighbor star. It was 43 degrees up, in Aquila, Azimuth 217 in the SW. However, with 22 second duration and using a long integration, it might just be doable. I'll be trying from Cabrillo Observatory at the end of Astro 8A class
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I tried this from Cabrillo Observatory. The target 14.6 star was not only blended with the brighter asteroid magnitude 13.1 and also, alas, with another 13th mag star closer than I had hoped. Kirk recorded from home at 16x Watec setting. I recorded at 16x as well.
Nolthenius
I recorded from the Observatory at Cabrillo, up against the wall of the storage building as the best compromise for all factors, near the table with students doing their projects. I used the dew shield and hope no light messed with the results, since the altitude was high and scope pointing up. I have tried many different ways of reducing the tape and while the occultation is there on the light curve, no reasonable strategy I can find allows it to pass the FP test. The best result was using a very nearby tracking star, a static aperture of tight 2.8 pixels set onto the target. I also tried using two tracking stars, as I usually do, to correct for field rotation in my alt-az scope, with one of the tracking stars being the asteroid itself. Unfortunately, the asteroid aperture didn't track and instead the tracking seemed to only follow the other tracking star. I also tried the 'lunar' aperture option but that did not help the red bar/blue bar test, in fact it was worse. I tried 'yellow mask default' options as well, but it was not apparent what that did, and the results still failed the 1/50,000 criterion applied by IOTA for being reportable.
There were oscillations in light level that occurred in all stars examined as possible tracking and reference stars in the last 2 minutes of taping, and not perfectly aligned in time but close (flexure??) and they were removed from the analysis, so only 5-6 minutes of data was used, which is evidently too little for judging this predicted very shallow observed 17 second long event as passing the 1/50,000 odds of being a false positive. The depth was predicted to be only 0.3 magnitude, but the recorded occultation depth in PyOTE was only 0.13 magnitude, perhaps because of light leaking in from the very close 13th mag star above the asteroid.
Here's the results, but they won't be reported as experience teaches me they'll be rejected anyway.. Given the timing error bars, it's probably only safe to say that, in realitiy, we had an occultation but not well enough timed to improve the orbit significantly, nor the shape.
While frustrating, given the software options, the timing accuracy and event rank, means we're not tossing out much in the way of good astrometry in this particular observation case.
The raw PyMovie data. The occultation is at center. Students nearby felt it safe, apparently, to start walking near the tripod legs on the stiff ground, 2 1/2 minutes after the event, possibly causing the oscillations in the target (and all other stars checked) light curves. |
The False Positive test. The red bar must be to the right of the black bar or the odds of a false positive in the sampled data is greater than 1 chance in 50,000. |
The "Robust Mean" plot, showing the distribution of pixel values. It looks skewed to the high side - neighbor star light is suspected. |
PyOTE solution. 2-sigma timing error of 6 seconds, which doesn't significantly improve the already factored orbital uncertainty as shown on the OW shadow lines. This solution above does not use "Appsum" option, which was tried but was not an improvement in the results. |
Kirk Bender
Fog came in during the event and made impossible an already difficult event.
We both also tried and recorded Bitias earlier in that evening. But it was too faint and too short and nothing but noise in our light curves.
