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More Pete's log

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Saturday, 4 Dec 2010

Tonight’s forecast is a bit “iffy” Since it’s freezing & windy and since ASSNE seems to have 4 scopes committed to tonight’s UMD event I’m gonna stay home and do my thing. The observatory’s open for ambient cool-down by 16:30 and given how early it gets dark, I’m out and focusing by 17:30 hrs. Seeing’s pretty poor so the plan is to concentrate on brighter objects.

The scope drives have been doing an occasional stop & go thing during a slew, and making a racket while doing so. The scope is well balanced without the dew shield – which I added to reduce reflections and to aid in determining where the scope is pointing in relation to the shutter opening. Because it weighs a pound or two, and because it’s several feet out from the scope central axis, I suspect that severe imbalance is straining the drives. So tonight I’ll run without the shield and see what happens.

207945 is a potentially hazardous 830 meter size Apollo presently 17.5 magnitude, 9 million miles distant, moving at 6.2’/hr. Uncertainty level is 2. Imaged 30sec, 2X2 binning, -30°C camera temp., guiding at 2 Hz from 17:42 – 17:52 hrs. Frames 1, 6 & 12 show dRA = -0.8 and dDEC = -0.8. S/N averaging 6.5

2010 SC41 is another potentially hazardous Apollo. This one’s a really bright 15.8 magnitude, and that’s because although it’s only 723 meters in size it’s only 4.8 million miles out. Uncertainty level if 4. It’ll be really ripping across the FOV as its apparent motion is 20.8’/hr. Imaged 15 seconds, with 15 second delays between exposures, 2X2, -30C, 2 Hz from 18:07 to 19:01 hrs. There are several other asteroids in the FOV and they’re traveling very slowly. Transparency is good even though seeing isn’t. By running for almost an hour there’s a chance that I can bag them too. Frames 1, 10 and 20 show dRA = -0.4’ and dDEC = -1.2’ S/N averages 13.7

The first “bonus” asteroid from SC41’s images is 15 km sized 6637 Degas. It’s 1.5 AU out, shining at 16.9 mag and moving at only 39”/hr. Frames 1, 41 & 92 are used for the astrometry. Due to the short exposures and my being too lazy to do a track ‘n stack, the S/N is poor. Fact, I have to ask the software to indicate the position of the bonus asteroids as they range from faint to really faint. In this case I can see the asteroid in the first and last frame. It’s inside the little red indicator box, right where it should be. The middle frame has a hazy area in the center with the S/N all the way in the basement at 3.7 Anyway, position is reported with dRA = +0.0’ and dDEC = -0.0’ Frame 41 had a dDEC of -0.1’ but I figured that it was within my margin for error. (Incorrectly, but more on that later).

The second “bonus” asteroid is 8.3 km sized 77627, presently 18.9 magnitude, 1.9 AU distant, moving slowly at 25”/hr. Stacking frames 1-10, 47-56 & 83-92, dRA =-0.0 and dDEC = -0.0 Even after stacking, the first stack only has a S/N of 3.3

153814 is a 1.4 km sized potentially hazardous Apollo now .52 Au distant, 18.9 magnitude, and moving at 1.1’/hr. Uncertainty level is 2. Imaged 4 min, 2X2, -30C, 1 Hz from 19:15 – 19:48 hrs. Frames 1, 4 & 8 show dRA = +0.1’ and dDEC = +0.0’ S/N runs from 7.6 to 6.1

2005 GC120 is a potentially hazardous Apollo 757 meters in size, 5.5 million miles distant, 15.7 mag, moving at 19’/hr. Uncertainty level is 2. An attempt is made to position the camera so that the asteroid enters the frame and exits the frame across the diagonal – to turn into a GIF later. But it’s position is pretty far off and by the time I’ve started it’s already entered. Imaged 15 sec with 15 sec delays, 2X2, -30C, 2 Hz Frames 2, 24 & 48 indicate dRA = +2.8’ and dDEC = +4.3’ As noted in earlier logs this error is associated with no perturbation correction in Astrometrica. S/N is a strong 17.9

2008 YU32 is yet another potentially hazardous Apollo. This one is 659 m in size, 18.7 mag, .34 AU distant, moving at 1.7’/hr. Uncertainty level is 4. Imaged 3 min, 2X2, -30C, 18 Hz from21:07 – 22:00 hrs. Although high cloud was rolling over by 21:43 hrs. Frames 1, 8 and 16 show dRA = +0.3’ and dDEC = +0.1’ S/N on the frames was 3.1, 3.4 and 4.9 respectively. There are many “bonus” asteroids here!

Bonus 1 is 2005 XX5. This asteroid was last observed at the end of its first opposition on 5 Dec 2005. It hasn’t been seen since. It’s supposed to be18.3 magnitude and right in the center of my frame, but it’s not. XX5 is lost, and stays lost.

Bonus 2 is 14 km sized 83722 – now 19.3 magnitude, 3.3 AU distant, creeping along at 24”/hr. Frames 1, 8 and 16 show dRA and dDEC = +0.0 with S/N ranging from 4.8 to 5.5

Bonus 3 is 5 km sized 89527 – now 19.3 mag, 1.8 AU distant, moving 35”/hr. Frames 1, 8 & 16 show dRA = +0.1 and dDEC = +0.0 S/N ranges from frame 8 at 3.5 to frame 1 at 5.5 I’m using every tool I have, including object overlays, to pull this one out.

Bonus 4 is 3.8 km sized 115365 – now 18.9 mag, 1.3 AU out, moving 41”/hr. Using the same three frames dRA = +0.1 and dDEC = +0.0 S/N is strongest in frame 8 (6.2) and weakest in frame 16 (4.5)

By 22:00 the cloud is pretty heavy and further observing isn’t possible. Although I could run the astrometry from within the house it’s quicker to stay out and finish here. I’m in at 22:40 hrs, and the 30 data points are emailed to the MPC.

Conclusions & lessons learned:

Minutes after submitting 10 sets of observations I received an emailed response from the MPC. Usually it’s just a confirmation of receipt but this time it read REJECTED OBSERVATIONS The observations on 6637 Degas have been rejected because of inconsistencies in the measures (as determined by their departure from great-circle motion).

Well, I spent a couple of hours today (Dec 6th) figuring this one out. First I duplicated the astrometry on frames 1, 41, 91. Results were exactly the same. Then I ran astrometry on frames 2, 42, 92. Frame 42 had a strong image instead of the smear in frame 41 due to temporarily horrible seeing. RA and DEC results were then plotted and statistically analyzed. It turns out that the reported position for frame 41 was more than 2 arc-seconds off in declination. Frame 42 was right on the regression line where it should be.

Without the dew shield the drives showed no sign of overload this evening.

I’d originally planned on creating GIF “movies” of 2010 SC41 and 2005 GC120. But that requires hours of effort. Maybe some other time…….

Hgp 6 Dec 10
Pete P.