MDM Trouble Report for 2016 Feb 13

Telescope: 2.4m
Observer(s): John Thorstensen (Dartmouth)
Instrument: modspec + echelled

Problem(s) Encountered:
Glossing over the glitches to get to the actual problem: Around
midnight, the telescope started intermittently jittering by a 
few arcseconds; it would track ok for a while, and then start
moving around randomly, with jitters and little jumps every 
few seconds or more often.  I was able to get enough light down
the slit from brighter targets, but fainter or crowded objects
were not possible.  

I just can't figure out what this is.  It is not related to the 
autoguider -- it happens even with the guider off and the 
autoguider panel switch turned off. Even more strangely, it seems
to involve both axes!  It was definitely not wind shake, since
the winds were modest and the motion larger than any wind shake
I've seen with this telescope.  The dec encoder readout does
not change while the telescope is jiggling. The jiggling does 
not appear periodic at all. It first appeared when the telescope
was in the far west, but it occurred near the zenith at the end
of the night; curiously, one target in the far east at the end
of the night did not show the shake.  

I used the slit viewing camera to record some examples of the
shake -- they can be played back with DS9.  

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Submitted on 2016 Feb 14 [7:18:52]