Occultation of TYC 1218-00983-1 by Juewa - June 28, 2009

This occultation of an 11.7 star (r=11.2) was predicted to be a tough event (the Preston prediction page is here) - rising in the east and only 20 degrees above the horizon, and already near the magnitude limit of my system. And, the path was far away - requiring a drive to just north of Paso Robles to make the odds of success reasonably high. But weather was good, it was a Saturday night, and David Dunham and Walt Morgan were going through the much larger efforts of setting out multiple unmanned stations. And I knew that if I had a successful record, I'd feel it was all very much worth the effort. The problem was, that I was also already committed to be the support person for Dave Delucchi and Rick Ferrell's biggest training day of the summer - running from the bottom of Mt. Hamilton to the top, and I needed to drive straight from the occultation to Rick Ferrell's. Follow that adventure on this webpage.

I chose a location far enough into the northern part of the path that I could get a 2/3 odds of success. This was 57N track, and was also at a site a knew well - Nacimiento Road near the south end, where the turnaround is for the Wildflower Half Ironman Triathlon bike course. It's rural foothills, quiet, and promised dark skies and good odds of success. I arrived at 2:15am for the 3:53am event, and got set up without problems. The temperature was in the mid 60's, seeing was pretty good for 20 deg altitude, skies were moonless and also cloudless as near as I could tell, and the Milky Way overhead was brilliant. I could tell that there was significant extinction at low altitudes but the star's visibility rapidly improved as it rose, and by 20 degrees altitude was quite acceptable. On the map, ignore the telescope icon position - I continue to have trouble getting OW to place my chosen observing locations. I was actually about 2/3 of the way from King City to Paso Robles.

The target star was visible by eye in the 22mm Nagler in the 10" LX200, faintly. On the camcorder screen of the Canon ZR45mc with PC164CEX-2 video camera, the star was almost invisible and so hard to follow that I could not be sure I had an occultation, but it seemed to have been impossible to follow a few seconds before the predicted center of the occultation. I used a firewire connected to my Dell XPS M40 laptop to control the camcorder using Windows MovieMaker, and created an .avi file, which was then converted to a form useable by Limovie by using Virtual Dub - (juewaJune09vd.avi).

That's me, with Sagittarius above my head, just before the event

Screen capture off my laptop of the Limovie panel, showing the yellow circle around the tracking star, and blue/red circle around the faint target star

The Limovie light curve does indeed seem to show a valid occultation (blue curve). The yellow light curve shows a drop out a few seconds later, when Limovie lost tracking for some unknown reason. I paused Limovie, re-adjusted the aperatures to be on top of the stars, and resumed - ignore the brief drop out. The actual occultation is in the blue curve, about midway in the time window shown.

The noise distribution about the Occular 4.0 solution appears nicely Gaussian

The Occular 4.0 solution. A "Final Report" attempt crashed; not sure why. Might be because of a few dropped frames? The best solution is shown in green; a 4.77 second duration event - essentially exactly the predicted duration for a central event, but 4 seconds early.

Reduced profile of the asteroid - massive enough to have pulled itself into a sphere and not gotten knocked around too much since formation, it seems.

Tony George volunteered to run my .csv file through his own Occular to produce this final report (above)


D: 10:53:46.654 UT, accuracy~0.1 sec

R: 10:53:51.427 UT, accuracy ~0.1 sec

Site: Bradley, CA (on Nacemiento Lake Rd)

W. Long= 120deg 50' 40.2" N.Lat= 35deg 50' 10.25" Elev=686ft WGS84, 57.66km north of centerline

Excel report sent to IOTA on June 29, 2009

Final reduction profile from Brad Timerson