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            OBSERVING INSTRUCTIONS FOR STAR CLUSTER PLATES
            ----------------------------------------------
                         2nd Draft
                         7 Dec 2001

This draft incorporates comments and corrections from the observers.
It is checked into the "sdssTests" product.

Each star cluster plate has several pointings (tiles) associated
with it, where each pointing is offset by ~0.2 degrees and has
holes drilled for a different magnitude range of stars.  There are
a total of 4 plates with 19 pointings (tiles).  For details of
these plate designs, see:
  <A HREF="http://www.astro.princeton.edu:81/sdss-spectro/msg.766.html">sdss-spectro/766</A>

Required Weather Conditions
---------------------------
These plates must be observed in good conditions: photometric, reasonable
seeing, but the sky can be bright -- moon is OK.  They should also be
observed near transit except for N752 which is too close to the zenith
at DEC=+37.  Suggested starting observing times:
  N752     LMST= 3h    MST ~10pm in Dec <-- This is 1 hr after transit
  Pleiades       3h    MST ~10pm
  N1817          4h30  MST ~11:30
  Praesepe       8h    MST ~3am
We expect it to take between 60 and 90 minutes to observe the full
sequence for each of these plates once they are mounted.  If any
pointings have to be skipped due to time contraints, do not skip
the last (spectro-photometric) pointing.


Plugging + Mapping
------------------
There's one bit of special instructions for plugging these plates.
There will be an obvious line of 9 or 10 holes emanating from guide
fiber #11 (explained below).  It would be preferable if these are
not plugged with adjacent fibers in a fiber bundle.  That is, when
plugging, plug one fiber in one of these holes, plug the next fiber
from that bundle elsewhere, then another on one of those holes, etc.

When one of these plates is mapped, it produces several plPlugMapM
files -- one for each pointing.  These will be called, for example,
  plPlugMapM-0798-59999-01.par
  plPlugMapM-0798-59999-01B.par
   ...
  plPlugMapM-0798-59999-01D.par
Each plug-map contains exactly the same fiber->position information,
but specifies which fibers are real objects.  The Yanny header of
these files also has the correct RA,DEC for each pointing.

Observing: Goto field
---------------------
To go to the 1st pointing of the Praesepe plate (for ex):

  SOP> loadCartridge plPlugMapM-0798-59999-01.par
  SOP> gotoField

Observing: Pre-Calibrations
---------------------------
Take the normal sequences of pre- and post-calibrations:

  SOP> preCalibs

Observing: Getting offsets
--------------------------
We use a subset of the guide fibers for each pointing, but always 5 for
the first pointing just so we can get the offset, scale + rotation well.
The guide fibers appropriate to that pointing should appear in the guide
camera.  To be extra cautious, you could enable/disable the appropriate fibers:

  SOP> enableFiber 3 5 8 10 11  <--- (Actually must be done 1 fiber at a time)
  SOP> disableFiber 1 2 4 6 7 9  <--- (Actually do 1 fiber at a time)
  SOP> startGuider 1  <--- These are bright guide stars

Then you will want to make sure you are guiding well on the field with
a good scale and rotation.  **Definitely** save your offsets:

  SOP> stickyOffsets

Observing: First N-1 Pointings
------------------------------
All the observations will be smears.  The smear command for each pointing
is in the table below.  For ex, for the 1st Praesepe pointing:

  SOP> stopGuider   <--- Turn off guider!!
  SOP> smear 2.5 3.0 240 -nswath 1 -nogcam  <--- Take 3 such exposures!

Always take 3 exposures for each pointing.  Smear should always return
you to the start position, which can be checked on the guider.

For the next pointing, you will need to load the next plug-map, go to
the field, guide for a short while if the stars aren't in the center of
the fiber, turn off the guider, and issue another smear command.  For ex:

  SOP> loadCartridge plPlugMapM-0798-59999-01B.par
  SOP> gotoField
  SOP> enableFiber 1 4 6  <--- (Actually do 1 fiber at a time)
  SOP> disableFiber 2 3 5 7 8 9 10 11  <--- (Actually do 1 fiber at a time)
  SOP> startGuider 1  <--- These are bright guide stars
       ...
  SOP> stopGuider   <--- Turn off guider!!
  SOP> stickyOffsets
  SOP> smear 2.5 3.0 18 -nswath 1 -nogcam  <--- Take 3 such exposures!

Observing: Last Pointing
------------------------
The last pointing is special, in that it takes the plate to the
nearest SDSS primary standard and puts it down guide fiber 11.
There are 5 fibers spaced every 1 arcmin north of this guide fiber,
and 5 to the south.  There is a new SOP command "decSmear" which
(hopefully!) will move the telescope such that this star tracks
through those fibers.  (The normal "smear" command always smears
in elevation.)  The default speed of 1 arcmin/minute results in an
effective exposure time of ~3 sec, which is good for these stars.

The "decSmear" command will have to be sourced from a CVS version of IOP,
or copied from "sdsshost:/home/schlegel/decSmear.tcl".

These primary coordinates were from the same erroneous source as SOP,
so we expect some small offsets to find these stars:
  HD 84 ... offset in RA by +5" 
  HD 19 ... offset in RA by -3"
  BD+21 ... offset in RA by -8"

  SOP> loadCartridge plPlugMapM-0798-59999-01D.par
  SOP> gotoField
  SOP> enableFiber 11  <--- (Actually do 1 fiber at a time)
  SOP> disableFiber 1 2 3 4 5 6 7 8 9 10  <--- (Actually do 1 fiber at a time)
  SOP> startGuider 1  <--- These is a bright star
       ...
  SOP> stopGuider   <--- Turn off guider!!
  SOP> stickyOffsets
  SOP> decSmear 5.5 1.0  <--- Take 3 such exposures!

Again, always take 3 such exposures.  Smear should always return
you to the start position, which can be checked on the guider.

Observing: Post-Calibrations
----------------------------
Take the normal sequences of pre- and post-calibrations:

  SOP> postCalibs

Observing: Other Tests
----------------------
Once all of the above it done, and you have some time to kill before
that pot of espresso is done, it would be worth testing the decSmear
a bit more heavily.  In the above, we did 1 swath that moved the SDSS
primary star through the 5 fibers north of the guide fiber.  You could
test moving through the 5 fibers to the south with:

  SOP> decSmear 5.5 -1.0

You could also test doing a 3-swath decSmear which, like smear, spaces
the smears by 2.5 arc sec in order to approximate an aperature that
is wider than the fiber:

  SOP> decSmear 5.5 1.0 -nswath 3

Is the Data Good?
-----------------
My advise would be to look at the extracted spectra on the sos.apo
machine.  These are the files
  /data/spectro/spectrologs/$MJD/sci-$PLATE-$CAMERA-$EXPNUM.fits
You can look at them with the ATV command on sos.apo, as described at:
  http://sdsshost.apo.nmsu.edu/sdssProcedures/spectro_apodisplay.html#display_idl


Cluster   PLAT  RA    DEC    rmag  Guide fibers  T_max   smear command
--------- ----  ----- -----  ----  ------------  ------  ---------------------------
Praesepe  798   130.0 +19.6  12.0  3,5,8,10,11   142     smear 2.5 3.0 240 -nswath 1
          798B  129.8 +19.6   9.0  1,4,6           9     smear 2.5 3.0  18 -nswath 1
          798C  130.2 +19.6   5.9  2,7,9           0.5   smear 2.5 6.0   2 -nswath 1
(HD84937) 798D  146.9 +14.3   8.2  11              4.3   n/a
--------- ----  ----- -----  ----  ------------  ------  ---------------------------
Pleiades  799    57.0 +23.7  13.9  3,5,8,10,11   820     smear 2.5 3.0 600 -nswath 1
          799B   56.8 +23.7  11.1  1,6            62     smear 2.5 3.0 120 -nswath 1
          799C   56.6 +23.7   8.3  4,7             4.7   smear 2.5 3.0   9 -nswath 1
          799D   57.2 +23.7   5.5  2               0.4   smear 2.5 7.5   2 -nswath 1
          799E   57.4 +23.7   2.9  9               0.03  smear 2.5 50    1 -nswath 1
(BD+21)   799F   63.3 +23.1   9.1  11              9.9   n/a
--------- ----  ----- -----  ----  ------------  ------  ---------------------------
N752      800    29.2 +37.7  12.0  3,5,8,10,11   142     smear 2.5 3.0 240 -nswath 1
          800B   29.0 +37.7   9.0  1,4,6           9     smear 2.5 3.0  18 -nswath 1
          800C   29.4 +37.7   6.0  2,7,9           0.6   smear 2.5 6.0 1.2 -nswath 1
(HD19445) 800D   46.6 +26.9   7.9  11              3.2   n/a
--------- ----  ----- -----  ----  ------------  ------  ---------------------------
N1817     801    78.0 +16.7  15.2  3,5,8,10,11  2718     smear 2.5 3.0 600 -nswath 1
          801B   77.8 +16.7  12.8  1,6           298     smear 2.5 3.0 450 -nswath 1
          801C   78.2 +16.7  10.4  4,7            33     smear 2.5 3.0  60 -nswath 1
          801D   78.4 +16.7   8.0  2,9             3.6   smear 2.5 3.0   6 -nswath 1
(BD+21)   801E   63.2 +23.0   9.1  11              9.9   n/a
--------- ----  ----- -----  ----  ------------  ------  ---------------------------

In the above table, the maximum effective exposure time was computed
from the brightest r-mag object in each pointing by:
  T_max = (900 sec) * 10^((r-14)/2.5)
For the default smears which move +/- 3.0 arcsec in elevation, the
effective exposure time is about half the smear time.  Thus the smear
time can be 2 * T_max without saturating.

In order to prevent too short of an exposure time, the "deltaaz" in the
smear command is increased for the brightest objects.  For the 3rd mag
star in Pleiades, we smear across +/-50 arcsec in 1 second, resulting
in an effective exposure time of 0.03 sec.

-David and Scott