Astrometry's back up and running

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Astrometry's back up and running

Unread post by Pete » Mon Nov 14, 2016 6:22 pm

Observatory log - 13 Nov 2016

At long last the summer schedule of visual observing is ended and the SBIG camera’s been remounted to the 14”. Full setup is a 2-day affair. Tonight’s two primary objectives are 1) to focus and align the camera in preparation for taking flats 2) to stumble through the somewhat complex (to me) process of doing precision astrometry, as I tend to forget things after a long hiatus. Secondary objective is to nail a couple of bright easy asteroids.

Although I’m out by 17:48 there’s a good 60 minutes of preparation for first image, and at -5°C there’s a hint of frost on the imaging chip.

Air is calm and transparent. There’s a full “supermoon” half way up the eastern sky. Air temp is steady at 45°F.

433 Eros is a main belt asteroid discovered way back in 1893. It’s a brilliant 13.5 magnitude and motion is 55 arc-seconds/hour. After 123 years one would expect the current uncertainty level of 0, but there’s a surprising RMS residual of 0.65 arc-seconds. Imaged without flats and using auto-dark, 2X2 binning, -5C cooling, 2 Hz guiding. There’s a 19.3 magnitude asteroid also in the FOV so I got overly ambitious and the first frames were 3 minute exposures that completely oversaturated Eros. 1 minute exposures were also oversaturated. Successfully imaged from 19:03 – 19:13 at 30 sec. The delay didn't really hurt as Eros was occulting a faint star until after exposure got squared away. Frames 1, 5 & 9 show dRA = +0.3’ and dDEC = +0.1’.

Ahhh! I know the astrometry is good (S/N at 110/1 and FWHM at 3.9”). But the error in position reminds me that I’m using the ephemeris data from last May, and not the daily update that’s sitting on the flash drive awaiting loading. Just one of many things forgotten and relearned tonight.

2016 VC1 is a 330 meter sized potentially hazardous Apollo discovered just 9 days ago. It’s presently 18.3 magnitude and 9 million miles distant. Uncertainty level is naturally high at 7, and apparent motion is 7.8’/hr. Initial setup was 38 seconds, 2X2, -15C, 5 Hz. But frost started growing quickly and the camera temp was brought up to +3C as the imaging progressed from 19:32 – 19:49 hrs. Frames 1-4, 5-8 & 9-12 show dRA = +0.2’ and dDEC = -0.6’. S/N no lower than 6.3 and FWHM no larger than 5.4”. Good numbers. So that’s it for the night.

In at 20:00 with 6 observations forwarded to the MPC before the game started.

The last time I was out here working asteroids was May 12th – a full 6 months back. As my eyes grow dimmer visual work just isn’t as pleasing as it used to be so it’s good to be back out working the asteroids.

14 Nov 2016

Regenerated the desiccant plug 4 hours at 350° today and it’s reinstalled. Next clear night I’ll run some flats and be good for the winter.

Pete P.