MDM Observatory 2.4m Telescope Observer's Report for 2006 Jul 01

Observer(s): Armstrong, Piscionere, 
Institution(s): Columbia

Instrument: Templeton/direct

Worked for 4 hours (part of the night)
Conditions were Mixed most of the night.
Problems were encountered, see the separate trouble report for details.

Seeing and Weather:
   Clouds from 8pm until 3am.
   Beg: Overcast, Winds Calm
   Mid: Seeing 3 arcsec, Cirrus, Winds Calm
   End: Seeing 2.5 arcsec, Cirrus, Winds Calm

Observing Summary:

Thunderclouds and lightning kept us shut until 22:00; then it 
cleared enough to open.  Observed for a couple hours, then
had to close again at 1:00 (clouds.)  Opened again at 3:00.

Strange, transient problem with the CCD images:

At HA: 00:50:40.94  Decl +77, we began taking 3-second focus 
images in BG38 filter, spaced several seconds apart.  For roughly
half of the images, a dark smudge appears over ~ 1/3 of the 
field.  Looks a little like a fingerprint shape, and is not in 
the same place on each of the marred images.  Stars within the 
smudge area have trails; stars outside appear normal.  

No correlation between appearance of smudge and quality of 
seeing (although seeing was pretty awful: couldn't get it better 
than 3 .)  Tried decreasing the tracking rate to see if we could 
eliminate the trails - no change.

These images are saved in: /data/jk/n01/rwumi/.  The bad ones are 
ccd.001, 002, 003, 004, 013, 014.

We soon realized clouds would preclude us from getting good 
data on this faint object, so before starting the run we switched 
to HA 00:07:57.38  Decl +45, *staying in same filter*, with no 
further appearance of the smudge.  Then switched to V filter:
no trouble.

So a filter problem is ruled out.  And the shape of the dark
patch does not suggest a shutter problem.  All I can think of 
is an HA- or Decl-dependent problem.  Light leaking into the ccd
when telescope is tilted at a certain angle?

The seeing is another issue: our focus runs gave minima
no better than ~ 2.5 .  Perhaps the reason for this will be 
easy to determine tonight, as our brains have adjusted to the 
night schedule.

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Submitted on 2006 Jul 2 [11:55:26]