20230526

Guider offset (/plate scale) test at different declinations

After noticing that the same commanded HETDEX dither results in different sizes of dithers at low and high declinations, we want to characterize this apparent behavior and try to understand how to fix it (and possibly remove or add a cos(Dec) term as necessary).

This test should be attempted when the following conditions are met:

1. Moon up, no other Pr1 targets in the queue
2. Stable conditions, <2" DIQ without large variations, transparency >50%
3. Relatively fresh stack (no need to stack specially for this), with tRSE<150

If it looks like you can do it soon, plan ahead and run target_setup in advance to run shuffle on each star of your choosing. Each test should take about 10 minutes total (~5min to set up and ~5min to run the script).

This table includes the declination ranges we have successfully targeted and those which still need observations:

Dec range	Exact Dec	UT Date	script start time
-10 to 0	-04:52:52.47	2023-06-02	09:11 UT
0 to +10	+04:06:49.35	2023-05-31	07:25 UT
+10 to +20	?	YYYY-MM-DD	HH:MM UT
+20 to +30	?	YYYY-MM-DD	HH:MM UT
+30 to +40	+33:39:43.21	2023-05-30	08:10 UT
+40 to +50	+47:38:59.18	2023-05-31	08:10 UT
+50 to +60	?	YYYY-MM-DD	HH:MM UT
+60 to +70	?	YYYY-MM-DD	HH:MM UT

Procedure

0. Pick a target in the "GalPoint" catalog on htopx, run target_setup on Zeus for this target on the center of the IHMP position (IFU=000) like this:

   [stevenj@zeus ~]$ target_setup 26 W -ifu 000 -cat gp -to
   

1. go_next on this target with the usual setup commands.

2. Keep the ACQ camera running *AT ALL TIMES*. Use SDSS g` filters on ACQ and Guiders.

3. Ask the TO to:
   1. set up on the fake ACQ camera image with any star marked
   2. carefully center the guide star in the guider
   3. handshake to a Guider
   4. activate a WFS
   5. Keep the ACQ camera running and storing images throughout!
   6. Draw a very large guide box on the guider and ACQ camera
   7. Check that the Guider and ACQ cameras are getting good centroids/metrology throughout

4. Wait 3 minutes after WFS activation for focus to settle.

The remaining steps assume the Guider exposure time to be 5-6 seconds (if conditions are too poor for that we should not attempt this test). Note that while Guider 2 is not functional this test must be performed on Guider 1:

5. Run the script below, which will take about 5 minutes to complete:
   /data1/archive/users/stevenj/run_gc1_offset_test.sh
   This script will offset the Guider1 fiducial as described below:
   1. offset guider fiducial by dX,dY= -2.5, 2.5 arcsec, wait 1 minute
   2. offset guider fiducial by dX,dY= 5.0, 0.0 arcsec, wait 1 minute
   3. offset guider fiducial by dX,dY= 0.0,-5.0 arcsec, wait 1 minute
   4. offset guider fiducial by dX,dY= -5.0, 0.0 arcsec, wait 1 minute
   5. offset guider fiducial by dX,dY= 2.5, 2.5 arcsec, wait 1 minute

6. Test is complete, resume science observations.

7. Update the data table at the top of this page to indicate the date/time of the declination of this test.