MDM Trouble Report for 2005 May 12

Telescope: 1.3m
Observer(s): armstrong (columbia)
Instrument: templeton/direct

Problem(s) Encountered:
(If this is confusing, just find me tomorrow; I'll explain better.)


Images are in:  eve/n05/boo-trouble/
Here's what they show:

  ccd.001, ccd.007, ccd.008, ccd.009
     all show strange brighness pattern (which I'm about to explain)
  ccd.bg-dots
     shows same pattern, along with  dots  that look like water
     droplets
  ccd.bg-fine.fits
     taken just past point where guider problem disappears.  


Here's what happened:

Flats were all fine (at 2.5 hours east, +31 57)

Slewed to 12 39 -03 30   and took BG38 image.
It's got a horizontal streak of brightness across it.  Not
clearly-defined, but a gradual fading.

Tested all filters: All images in B, V, R, I, BG, GG show this strange
brightness; seems most pronounced in I, BG.  **U is normal**.

The guider is at x=5000, y=5000, and partially obscured (black across the
top.)  Moving y to 7000 makes this go away, but does not change ccd image
problem.

Took a BG38 FLAT - same problem.  But the earlier flats were
all fine.  SO THE CHANGE OF COORDINATES CAUSED THIS PROBLEM.


To test whether brightness pattern is coordinate-dependent:

Slewed North to +26 33 --> took another BG38 flat.  it's FINE.
took BG38 image  --> FINE.

Move guider back to y=5000 --> guider camera not obscured.
Took bg38 image --> FINE.

Slew down to +07 13 -->   bg38 image = fine.
Slew down to +01 57 -->   bg38 image = fine
Slew down to -03 39 -->   GUIDER OBSCURED AGAIN !!

With hand paddle in control room,  set North.   Moving up through
-3 36 30, guider obscuration disappears again *rapidly* - within about
30 .
At -3 37 20, top part of guider completely obscured.
At -3 36 7, guider is FINE.


So at the declination of ~ -3 36, this just suddenly happens.  Perhaps
filter wheel is unstable, and shifts once telescope inclination
angle is this low?


In case this is illuminating:
  UT 3:31:32
  LST: 11:25:13
  HA: -1 13 14.5
  Airmass ~ 1.3
  Dome azimuth 176 (it's correct)


(I went on to 15 07 +52, with no more problems.)


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Submitted on 2005 May 12 [4:34:15]