July 2001 anneal report for program 8841.

There was an anneal of the CCD on 11 July 2001, 71 days after the previous
anneal on 1 May 2001 due to STIS safing in May.  A homogeneous set of data was
obtained from proposal 8841:  The CCD Hot Pixel Annealing.

Due to the safing, and subsequent switch to Side-2 electronics, there is no
control loop feedback for temperature regulation of the CCD.  Thus the cooler
runs all the time at a lower temperature, but this temperature fluctuates.  The
fluctutation in temperature causes the dark level to fluctuate too.

So in order to keep the analysis of the annealing process consistent, it is
necessary to scale the darks to a reference temperature, 18 deg C, measured
off the CCD temperature housing and printed in the header keyword OCCDHTAV.
This scaling is identical with that done in the pipeline to scale darks.

Because the CCD is operating at lower temperatures, there is an offset between
the May and June anneal data.

1) The number of post-anneal hot pixels has decreased at all levels due to
   the extended period of being shut off, and due to the CCD operating at a
   lower temperature.

   > 0.1 e/s: 15866 pixels on Jul 11, 2001
   > 1.0 e/s:  3278
   > 10. e/s:   379
   
   > 0.1 e/s: 17012 pixels on May 1, 2001
   > 1.0 e/s:  3455
   > 10. e/s:   389
   
   > 0.1 e/s: 17042 pixels on Apr 7, 2001
   > 1.0 e/s:  3473
   > 10. e/s:   389
   
   > 0.1 e/s: 17151 pixels on Mar 11, 2001
   > 1.0 e/s:  3452
   > 10. e/s:   397


2) The *raw* post-anneal dark countrate for this anneal is 0.02439 cts/pixel.
   This compares with 0.02608 cts/pixel on May 1, 2001, and 0.02267 cts/pixel 
   a year ago.

3) The iterated median count rate (after iterating up to 30 times by
   eliminating pixels +/- 5*sigma) is 0.00384, down from May.

4) The creation rates for hot pixels over this period give odd results due to
   the extended period of being shut off during the safing and the lower
   operating temperature of the CCD.

   > 0.1 e/s: -205.8 pixels/day in Jul 2001 
   > 1.0 e/s:  -53.0
   > 10  e/s:  -10.6

   > 0.1 e/s:  37.3 pixels/day in May 2001 
   > 1.0 e/s:   6.9
   > 10  e/s:   0.2

   > 0.1 e/s:  12.8 pixels/day in Apr 2001 
   > 1.0 e/s:   0.2
   > 10  e/s:  -0.9


   > 0.1 e/s:  40.2 pixels/day in Jul 2000 
   > 1.0 e/s:   4.4
   > 10  e/s:   0.2


5) The rate at which new hot pixels annealed out was within the normal range of
   fluctuations.

   > 0.1 e/s:  29.4% annealed away in the Jul 11, 2001 anneal
   > 1.0 e/s:  45.9%
   > 10  e/s:    53%
   
   > 0.1 e/s: 103.5% annealed away in the May 1, 2001 anneal.
   > 1.0 e/s: 111.4%
   > 10  e/s: 100.0%
   
   > 0.1 e/s: 132.8% annealed away in the Apr 7, 2001 anneal.
   > 1.0 e/s: -425.%
   > 10  e/s:  65.0%


   The usual plots are attached.