MDM Trouble Report for 2010 Sep 27

Telescope: 2.4m
Observer(s): S. Lepine (AMNH)
Instrument: Direct + Echelle

Problem(s) Encountered:
The Echelle camera displayed what looked like charge transfer
efficiency (CTE) problems. The problem was intermittent. 
When it occured, point sources were observed  leaking  
up along the columns, displaying characteristic looking
 comet tails . 

Re-cycling the power on the camera failed to fix the problem.

After experimenting with various exposure times/targets, 
I found that the problem systematically occurs whenever the 
background counts on the chip are low, typically less than 
1000 counts/pixel (the bias level is 500). Short 1-second 
exposures on very bright stars produced the most dreadful 
effects; however long exposures on faint sources, with a high 
sky background, appeared to be unaffected.

My conclusion then is that a minimum level of counts over all
the pixels is apparently required for the chip to transfer 
charges properly. Note that this would also explain the 
very unusual patterns observed in the bias frames.

One possible fix then is to work with long exposure, so that 
there's always a minimum level of sky background on each 
frame. This is what I ended up doing, with apparently
good results. Unfortunately our astrometric program has 
mostly bright targets, which all require short exposures, and
I'm running out of faint ones.

A different camera (Nellie) should thus preferably be 
used for the remainder of this run.


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Submitted on 2010 Sep 28 [6:40:39]