Occultation of a 12.0 star by 10.5 magnitude Athamantis Feb 3, 2009 - Cabrillo Observatory

This occultation would test my ability to detect small mag drops. The predicted drop was 0.24 magnitudes. Since the combined image was fairly bright, I figured the point to point scatter would be less than a factor of two and averaged over a few points, would be fairly straightforward to see as long as the event was at least 1 second. The predicted central duration was 10 seconds, but I was on the edge of the southern 1-sigma zone. I used MovieMaker, then VirtualDub to get an uncompressed .avi file, and ran LiMovie and then Occular.


This is a capture of the image. Athamantis is at upper left and a brighter star is in the red/yellow circles at right.

Below, in LiMovie I used 7-10-25 radii and had it track with Sych-APT and Link Tracking. I had Occular search for events lasting at least 3 and less than 12 seconds. The center of the predicted event time is 10:35:17 UT which corresponds to frame 958. 10 seconds is 300 frames. The odds of a 10 second central event giving only a 1 second graze is very low and the data is too noisy to detect such an event.

Occular plot of the light curve (blue) and figure of merit (black). There is a peak in FOM about 1 second after the predicted time, but there are competing peaks which are not plausible, and the plot looks consistent with no occultation.

Noise plot shows Gaussian form, which is good.

Just in case the photometry aperature was too small and starlight was often spilling outside the circle, I re-did LiMovie with a larger 13/15/25 set of radii. If I can figure out how to bin the data and replot, it would be easier to tell if there was a dip.

The one minute record extracted from the mini-DV tape, plotted by LiMovie.

Zoomed in to the 23 seconds centered on the predicted event time (frame 958).

Derek's full scale recording

Derek's record, zoomed in. My interpretation? I think he's got a distinctly more convincing event than my record. It would require almost no shift in the path to produce a short event for Derek and a miss for me. Too bad it was so brief and the drop so shallow - very tough to achieve statistical confidence.