Conducting the Wavefront Sensing Observations (Cassegrain)

Conducting the Wavefront Sensing Observations (Cassegrain)

Getting started.

Log in as observer on Ohi, Kauwa and WFDR1 and make sure that the dichroic has been moved to the WFS (east) port. Use Ohi to acquire the data; use WFDR1 (via Kauwa) to display the images with ORAC.

Align the two out-of-focus images (the “+1” and “-1” images) of the primary. These images will be displayed on a Gaia display, and should look something like this (note that the Gaia window will not appear until data have been obtained). To do this, slew to a CMC star near the zenith, then:

Run up the WFS EPICS screen on Ohi by typing

  > dm curve.dl &

This will open the curve epics display, as shown below. With the epics window set to “eng”, the data will be written in fits format to an engineering directory, /ukirtdata/raw/eng/curve/UTdate/. When the red exclamation mark appears in this epics display, this DOES NOT indicate an error, but it does indicate that the WFS is idle.

On WFDR1, run the curve version of ORAC-DR by typing

  > curve_init
> oracdr_curve_eng
> oracdr -loop flag

oracdr_curve_eng creates sdf images in the /ukirtdata/reduced/eng/curve/UTdate directory; each image is displayed on a Gaia display as it is obtained and converted. Set the exposure time to 5 seconds (NOTE – you have to hit RETURN while the cursor is in the “Exposure” window to get the exposure time to change), and take alternate images of the primary with the focus set to “+1” and “-1” (note – the focus will say “stopped” when the lens wheel move is complete). By making small changes to the WFS aperture with “aoff” (while guiding on the target CMC star), the two images should be roughly aligned. If the primary does not appear evenly illuminated, aligning the images with “aoff” should improve this also. Once the two images of the primary are aligned (to within about 10%), zero the new aperture with “azero” and report the new X and Y values to Tom Kerr and/or Russell Kackley.

Taking Data

The aim is to acquire 120 images, 2 images of each of 60 stars, with the telescope set to +1 and -1 metre out of focus. A script (WFS_QA.exec) is used to slew the telescope to the correct HA and decs and then take the data frames (A list of telescope positions is also available for manual operations). At each position, the cmc_a command is used by the TSS to select a nearby bright (8th mag) A star.

If you have left the EPICS screen up, leave it, otherwise run it up again by typing (on Ohi)

  > dm curve.dl&

On Ohi run  up the OCS as if running the normal cassegrain instruments:

  > ocs_up

When the sequence console appears, type ditscmd UKIRT_INST ADD WFS on Ohi. This will load the WFS tasks and will make the menu available in the sequence console.

Next go into the sequence console “File” menu, select “Load” and select the WFS_QA.exec.

Make sure the lens wheel is not at position +1 before starting to run the exec. The exec starts with position +1 and the WFS does not know how to move to a position where it is already at. It will hang if this is the case. The easiest way out is to move the lens wheel to a different position from the EPICS screen.

Change the directory to which the data will be written by clicking on the “/” on the EPICS screen.

On Kauwa run the curve version of ORAC-DR by typing

  > curve_init
> oracdr_curve
> oracdr -loop flag

As before, the acquired data will be converted to sdf and displayed with Gaia, although now the data are written to a non-engineering directory, /ukirtdata/reduced/curve/UTdate/.

Below is the procedure for taking the data.

  •  Run the script from the top using “run from highlight”. The telescope will slew to its initial position of HA=-3:50 dec=0. The TSS now selects an A star using the cmc_a command.
  • Once the star is selected, turn on guiding and hit the “continue” button. Repeat for 60 positions.

The WFS exec contains 60 pairs of observations, separated by breaks. When one pair of observations are complete the sequence will slew the telescope and then stop at the break.

  • Select a new CMC star, fast guide on target 
  • click on continue in the sequence console 

When you’ve finished, dismiss the epics display and ORAC-DR. There is no need to keep a written log, but please indicate in the shift comments the start and end number of the WFS sequence.

Reducing the Data

It would be helpful (though not essential) if observers “reduced” the output data from ORAC-DR in parallel with the data acquisition. This should be done on WFDR1: in an xterm, change directory to /ukirtdata/reduced/curve/UTDate/ . Here, run the reduction pipeline by typing

  > curve_init
> reduceall_new 1

Data will be reduced from file 1. A number of additional files will be created; “.zer”, “.wav”, “.int”, “.log” and “.pha” for every other reduced .sdf file obtained. A lot of images will also be displayed (via SAO Image) which may drive you bonkers – apologies for that!

And finally, as a last reminder, raw images are written to /ukirtdata/raw/curve/UTdate/, while reduced data from ORAC-DR go into /ukirtdata/reduced/curve/UTdate/. The results from “reduceall_new” are also written to /ukirtdata/reduced/curve/UTdate/

If you have a problem.

— You are unable to write data files to disk

While logged on as curve_dev or curve_eng, you find that on hitting the “expose” button you do not take any data (integrate) or write data to disk. No error is reported; however, nor does the “File Number” on the Epics display increment. An additional symptom is that there are error messages on the serial console talking about “error getting voltages” and a buffer overflow. This may be the result of the electronics rack being switched off since the last WFS run, but sometimes the array controller just hangs up too. This can happen in the middle of a run. To cure this, click on “other displays” on the epics screen and select “Reboot CCD”. If the problem persists, reboot the primary mirror VME crate in the computer room (from the computer systems console – select “primary” and reboot).

— Lens wheel not moving? 

If you suspect that the lens wheel is not moving, i.e. if the Epics display doesn’t say “running” when you click on +1 or -1, check the electronics rack on the telescope (the blue box containing the WFS electronics hangs above-left of the WFS black box when facing the telescope — just follow the cables from the WFS). For epics-controlled operation the Toggle switch should be set to “Rack” and the black filter selection knob must be at the 0 position; the seven segment LED will show the current filter position, which should correspond to the knob setting. With the top of the WFS black box removed, you can check that the lens wheel is moving freely when turning the black knob. The wheel should also move when the command is issued from the Epics display (after the filter knob is set back to 0). If the wheel doesn’t move, try power-cycling the electronics box (use the switch on the power strip at the back of the cabinet).

You could also check the optical fibre cable in the computer room. Behind the computer rack you should find that the dual-connectors of the two orange cables are properly connected together. If a recent visitor instrument has been using the cable, this may not be the case.

— You repeatedly get an error message from ORAC 

You may get the following ORAC error message from the WFS data, after each frame is taken:

  #9 Err: !! DAT_NEW: Error creating a new HDS component.
#9 Err: ! SUBPAR: Failed to obtain parameter file component
for parameter ORIGIN
#9 Err: ! SUBPAR: Failed to store array value for parameter ORIGIN
#9 Err: !! DAT__DIMIN: Dimensions invalid
#9 Err: Error in obeyw to monolith ndfpack_mon (task=setorigin):

This pops up even though the data look OK on the gaia display and the orac status window gives the thumbs-up:

 REDUCING: f19990907_00012.sdf
This observation is part of group g19990907_1
Using recipe QUICK_LOOK provided by the frame
Arguments were: ndf=f19990907_00012 origin=[,]

The reason for this (thanks Frossie): oracdr_curve treates the data as if the WFS was UFTI. The initial UFTI primitive tries to set-origin to the values of the RDOUT_X1 and the RDOUT_Y1 headers which do not exist in WFS data. The error is not fatal and you may ignore it.

— ORAC-DR has crashed/is not displaying images 

The raw data obtained when running curve_dev (and curve_eng) are written to disk as fits files; ORAC’s purpose is to display frames as they are taken and produce .sdf (NDF) files in the reduced directory. The “reduceall_new” command operates on these NDF files. Thus, if ORAC-DR crashes during the observations you will not be able to reduce the data with “reduceall_new”. Moreover, you will not get an automatic display of each image. The data can be converted to NDF and reduced later, so this is not a problem. However, to view each data frame as it is acquired you will need to open a Gaia display from the raw data directory and “open (display)” the raw fits files manually. Please check periodically that the image of the primary is present and well-illuminated.

— If you take a “bad frame” 

It is important that the data are taken sequentially with the focus set to +1 then -1. If you take a bad frame, you can repeat the observation, but it is important to repeat the entire pair, not just the bad frame. Hit stop asap in the sequence console and move the highlight to just below the previous slew command in the sequence and hit run from highlight. Please indicate you have repeated a pai in the shift comments.
Note that when the Epics display reappears, the file number should automatically be set to the next frame.