The Occultation by Bertha

Sun eve Oct 22, 2017

This fairly high rank event is at a convenient time, but a difficult altitude of only 10 degrees in the northeast, in southern Aries. The site that has the best odds and not too far away, is on Calaveras Rd, a turn out soon after crossing over the ridge, at 37d 26.88' latitude, elevation 1,000 ft.



I changed my plans to get to a gap in the coverage, driving up Hwy 1 instead. I got to my new planned site, at the road on the ridge above the Montara Hostel, and found that cypress trees blocked the 10 degree eastern horizon a total no-go! Drove back south a mile and thought I'd try heading towards the cliff-top "The Distillery", where I'd treated my friends to a very nice dinner before a trip to the SF Symphony many years ago. Took a turn and found a terrific eastern horizon as I paralleled the Half Moon Bay airport, and set up there. Skies were clean and perfect, and I was able to get on the target with the LCD even when the star was only about 5 degrees above the horizon. Made positive ID easily, and got a good video recording considering the rapid scintillation. I was amazed and disappointed to see that despite the 92% odds of a "hit", it looked like a miss. Now, it's the next night and I'm running it through LiMovie. Used 5/7/15 circles for photometry to avoid overlapping on the close companion, which was the comparison star. Circles tracked well but only after I re-started at 2:37:49, after the final re-centeringt adjustment. I actually took 2 more minutes of video data than is shown on the images below.

Now, the photometry looks a little more interesting. The deepest drop is to ~zero level for just one integration (which was on 4x or 2-frame integration, or 1/15 of a second. I may have had a ~1/8 second occultation, since the moment of the drop coincides with the predicted time of the event, to within 12% of the diameter of the asteroid (i.e. 2 seconds). Will have to see how it mates with the other chords before considering whether it is real. The two frames which would be integrated into a single blocked point are frames 1458 and 1459. The time stamps on each frame of these two frames is 2:38:09.1783 and 2:38:09.2117. With the -.0667 camera delay correction, and for a 1/8 second duration event (D half way between the unocculted and occulted frame, similar for R), that gives a D = 02:38:09.0620 and an R = 02:38:09.1950 UT. I'm not sure how to let Occular do an analysis of such a short event, so I took the times from the frame numbers and assumed the "D" and "R" would be halfway between the unocculted and fully occulted integrated frame points, directly from the LiMovie light curve, w/o using Occular.

70 seconds of data after the final re-centering. I have 2 additional minutes not included here. The deepest drop is at the predicted time of the event, but only for a single integrated frames point.

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