Test the image rotator function, by selecting and setting a
PA in the lower half of the GUI. The status windows in the
upper half of the GUI should reflect the change.
If the rotator does not respond, from XNIRSPEC Instrument Control,
select IROT, then Tracking On to enable the rotator.
After telescope pointing setup and focusing are complete,
proceed with acquisition of the first science object.
Make sure SCAM guiding is OFF (as broadcast in XNIRSPEC).
Tell the OA to point to REF with the object.
Use the XNIRSPEC SCAM Camera control to take an
image. Vary the integration time (minimum itime2 is 0.10 s) and
number of co-adds to avoid saturation (maximum well is 30,000 DN).
If the object is faint, click Set nod size and enter
small nod values (the SCAM FOV is 46 arcsec), and click Snapi
which will nod the telescope, take a sky frame, then nod back
and take an object frame, and display the result. SCAM exposures
normally need not exceed 60s under normal sky conditions.
In the , select Tel - Move Telescope,
which will prompt you to click on the object first, and
its destination next, which you should make
the spatial center of the slit (ie near the center of slit length).
Take another SCAM image, and use Math - Sdiff which
will display the difference between the last and current images
(making the object "black" or negative). You may optionally
tune up the position of the object using the
NIRSPEC Slit Nod GUI to make precision offsets
along or perpendicular to the slit; this may need to be
repeated after the first nod (and before the first exposure
of the nod sequence).
When you start a nod-exposure pattern from EFSgui,
additional SCAM exposures should be taken after each nod as
directed by the TCL pop-up windows (which state Verify
Pointing with SCAM). And, SCAM exposures
should be taken intermittently to check rotator tracking
` through the longer spectral exposures.
The minimum exposure time on the SPEC camera is 0.25s.
The maximum recommended exposure time is 900s, with 600s more
typical.
Bright objects can be guided on directly in SCAM while
nodding. This can be an efficient way to minimize setup overhead,
since the autoguider will nominally pull the object on to the
slit for small spatial deviations.
To guide on the SCAM, if the object can be readily
identified in its field, tell the OA to first acquire the
it on the offset guider (pointing origin REFA), and set
his collimations. Then, he/she should (if Set SCAM Guiding
ON, and point the object to REF. Next, the OA adjusts
the exposure time to avoid saturation, and then offsets from
10-30 arcsec in any direction, and makes a new sky exposure
(with MAKE SKY). Then, the object is reaquired, setting it on the
center of the slit. Once the guiding loop is closed, the
observer can start nod-spectral exposure sequences with
EFSgui.
The most efficient way to adjust pointing throughout the
night is to use the REFA pointing origin, or the
PXL offset CCD guider.
The OA simply selects a pointing star, and points REFA.
The star will end up near the center of the guider annulus,
but at a clocked position that is proportional to the current
image rotator physical position. The star ends up at 12 O'clock
at rotpposn=0.
Re-point the observer's science object to REF when
complete.
The NIRSPEC image rotator should be initialized fairly
frequently, at the very least in between objects. The rotator
initializes more rapidily for physical positions just CCW of center.
First, all guiding must be OFF. Then, the NIRSPEC operator
init's the rotator by selecting in XNIRSPEC Instrument Control,
Engineer, Motors, Init.
The rotator should instantly slew back to it's operating
position as determined by the current tracking position angle.
