Problems During Observing .. And What to Do

1. Images show bad amp

This is usually diagnosed by an amp appearing “dead”, having very large noise (mscstat results in rms > ~ 1000 adu/pix).

Can be usually fixed by typing the following in a NOCS xterm window:

• nocs reset ccp
• nocs init ccp

Then take two zero images. The first image is always bad. The second should be ok. Check it using mscstat <filename> once it has read out. All rms values should be between 4-7 adu (except for amps 6 and 14, which may be ~8-10).

2. 4MAPS system goes “OFF AIR” during observing

OA should notice this, but you can keep track of the mirror support system on the 4MAPS gui. If it says “OFF AIR”, the mirror is off air!

• Type Control-C to exit out of the observing script
• wait for it to finish and for “DONE” to appear on the NMSL gui
• type “ditscmd nohs nohs_endobs” in the xterm window in which the script was stopped. This should readout the last image and display it on the real-time display ximtool window
• Tell the OA they can move the telescope to zenith and reset 4MAPS
• Check the last image taken when 4MAPS failure occurred - the image quality is probably bad. Log the image file / exposure number
• Edit the mzls*sh script. This is a bit complicated, since you need to keep the first 8 lines of the script, and then delete everything up to the point where you stopped. The image number at which you stopped is probably displayed in the NMSL gui. Let’s say the last image was No. 14. You may want to repeat this image, if the image quality was bad due to the 4MAPS failure. So delete all lines for image exposures No. 1 to No. 13, but be careful that you retain the telescope positioning command in the script that occurs just before the line ==== No. 14 ==== .
• Once the OA has reset 4MAPS, you can restart the script. The telescope will slew to your position and start the exposure.

3. Shifted images

Every now and then, an image appears which shows a shifted region in one or more CCDs. Please log this. You can identify images with shifts by running

grep pixCnt mos3*dat | grep 1783

This results in all the files that may have shifts. Please examine them by displaying them using mscdisplay, examining the full image, identifying the CCDs which have shifts and logging the file numbers / exposure numbers

4. Repeat images

This is very hard to diagnose, and requires you paying attention to the images, and occasionally running the command:

hselect mos3*fits[0] $I,READTIME yes

in the IRAF window.

If the READTIME values begin to repeat, this is a sign that new images are not being written out. Another clue is that the read out counter on the NMSL gui goes straight from 44 to 0. A third clue is that the MOSSTAT command is failing to find any stars in the image, even though the offsets were small when the sequence was started.

If any of these are true, then it means that the images are just duplicates of previous images. You need to stop the sequence using CTRL-C in the window where the script is being exectuted, and restart everything:

• Stop MOSAIC (from the startup gui)
• In a NOCS xterm window, type:

nocs nuke pana nocs nuke dhs

• Start MOSAIC (from the startup gui)

Once everything comes up and you have rearranged windows how you like, take a ZERO frame to make sure that the amps are all OK. Check the noise on the zero image using mscstat. If this is not OK, then see instructions for Problem 1.

From here, it is best to make a new plan (strategy file) and start it up.

Log all the images that had identical READTIME values.

5. Focus drifting

If you lose track of the focus and don’t know whether you are below or above the focus value, stop the observing script by using CTRL-C, waiting for the readout to complete and the “DONE” to appear on the NMSL window, and then execute

• ditscmd nohs nohs_endobs

Then do a focus sequence.

• Create a focus script using the “Focus” button on the NGUI This pops up the following window:

• use a good guess for the mid-point, an instrument focus step of -100 (or -70, if the seeing is good), at least 7 focus iterations and a detector pixel shift of 30; Make sure you have chosen the zd filter
• execute the focus sequence
• edit the /data2/observer/mscfoc.cl script to change the file name of the focus image
• In the IRAF window, cl < mscfoc.cl and follow the instructions
• Once you have determined the best focus:
  • set the focus value in the MCCD window and hit “Apply”
  • log the Truss temperature and focus values.
• Edit the observing script to delete all the steps that have been done and start at a new image. Or create a new script
• Tell the OA that you have determined a new focus and changed the focus.
• Restart observing

6. Images of stars on the guider are bouncing around

• If the wind is high, ask the OA to close the louvers