Nod & shuffle using Taurus

Starting Up the Software System

Running Taurus and Observer

This requires the following steps:

1.    Log in to AAT40A as OBSERVER

2.    Type the following commands (this assumes that we are using X-terminal aatxtk and CCD controller 1)

xon aatxtk
rvtaurus ccd_n

This will start up the Taurus SMS user interface and an OBSERVER window to control the CCD.

3.    On the Taurus SMS interface enter the startup menu and choose option NONE or CCD.

4.    Type the . key on the numeric keypad to get a command prompt. Enter the following command:

load disk$user:[observer.icl_load]umd_nov00.icl

or whatever load file you use to set up TAURUS.

5.    Log in to AAT40A again as OBSERVER in another window.

6.     Type the command:


where "n" is the running OBSERVER CCD number (1 or 2). This will initialise the instrument sequencer and provide a window with an ICL> prompt from which charge shuffling runs are started.


This program is run from the VAX NIGHT account to accept telescope  commands (from the instrument sequencer).  Log into the night account on AAT40A and enter the following commands at the $ prompt.
define instseq_sif IRISTEST_SIF:
The TEL_CONTROL program will display the string "Ready" when it has successfully started. If it does not appear, then see the section Debugging.  Pay particular attention to the terminal server going down. The TEL_CONTROL program continues to run from this terminal.  To exit it at the end of the night, type EXIT.

Telescope commands sent by the instrument sequencer will  be reported on the terminal whilst the program runs. If the correct commands do not appear when doing a charge shuffling run you may need to reset the instrument sequencer (see  Debugging). This may be necessary after the Taurus charge shuffling mode has been used.

The Graphical User Interface

The graphical user interface is run from the solaris system aatssz. Log in on this machine as observer. Then type the command:

setenv DISPLAY aatxtk:0

The graphical user interface will now come up. It has three tabbed panels which can be used to set up parameters for nod and shuffle runs as well as two types of polarimetry charge shuffling runs. The programme will put the shuffle file into the disk$user:[observer.csx_files] directory. The window is taken from the default location but you can specify any window in any sub-directory with a full path name.

The last file sent to VAX is the one picked up by the nod-shuffle initiation below.

Taking Data

The Charge Shuffling user interface used to define nod-shuffle runs. There are two ways to nod on the sky: AXES or OFFSETS. The telescope needs to be tracking. The fundamental difference between the AXES and OFFSETS mode is given in the appendix below. You do not want to be using OFFSETS for large angle nods.

Here are tips for different observing modes:

A.    For sky flats and flux standards, use OFFSETS mode with an offset of zero. The set up is shown in the upper right figure.

B.    If you are doing diffuse H-alpha detection, which requires nodding over large angles, the most efficient way is to probably use AXES mode and turn off the guiding. The set up is shown in the upper left figure. In Sept/Oct 2001, we found that this was a good match to the maximum nod allowed in AXES mode, i.e. 1.26 deg. AXES position A is offset by +240mm to the S and W; AXES position B is offset by -240mm to the N and E. This messes up the RA, dec positions in the FITS headers. We recommend that the on-field RA, dec be editted into the log pages.

C.     If you are using microslits with TAURUS++, you will need to use AXES mode so as to guide on the on-source position. The set up is shown in the lower figure. In typical observations, the angular distance moved is only a few arcseconds.

If the load software cannot find mitll_nodshuf, there should be an up-to-date copy at disk$user:[]. The shuffle software will load this window for you even if you have the wrong window loaded before initiating the shufle.

Note: Some time, I need to check what nod distance runs you into trouble with the telescope shutter; this is presumably offsets bigger than a degree since 2dF has no problem.  We need to use "Follow Telescope" for nods of several degrees.

Command sequence for a nod-shuffle run.

So here is the sequence to initiate a nod-shuffle run.

1. Using the graphical interface set up the parameters for your run.

2. Click the Send to Vax button.

3. On the OBSERVER ICL terminal type the command SRUN.

This will start a charge shuffling run with the parameters set up in the GUI. The run takes some time to get going as it has to download information to the CCD micro and the instrument sequencer. Once the run starts you will see messages come out on the TEL_CONTROL terminal as the wave-plate is stepped.

If you want to repeat a run with the same parameters just type SRUN again.

Charge Shuffling Observation Parameters

The Polarimetry or Pol/Nod panels on the user interface are used for setting up polarimetry observations. The following parameters have to be set up:

Exposure time - This is the time in seconds spent exposing in each wave-plate position during each cycle.

Wait time - This is the time in seconds to wait for the polarimeter (or telescope in Pol/Nod mode) to settle after each move. A time of 3 seconds should be sufficient for straight polarimetry sequences. If Polarimetry plus Nodding is used the wait time must be large enough to allow the telescope to settle into position which may require a larger value.

Shift - The number of CCD pixels to shuffle by at each step. With the MITLL CCDs 400 pixels is a good number, shuffling far enough to keep the double images of the mask well separated.

Cycles - The number of charge shuffling cycles in the run.

Window - The CCD readout window to use. The MITLL_POLSHUFFLE window is a 1600 by 800 window large enough for four shuffles of the polarimeter field. It also has a 20 column bias region. There is also MITLL_CIRCSHUFFLE which is 800 by 800 large enough for two shuffles, as in circular polarimetry.

RA Offset - For the offset mode the RA offset in arc seconds (for polarimetry/nodding modes only).

Dec Offset - For the offset mode the Dec offset in arc seconds (for polarimetry/nodding modes only).

Going back to normal CCD observation

The system returns automatically to the appropriate mode for doing normal CCD observations when the run is complete. Occasionally, due to an error, it may remaining in shuffle mode (indicating by the prompt). In this case, type "METHOD DEFAULT" in the Observer window or at the ICL> prompt.

Aborting Shuffling operations

To abort a shuffle, type ABORT in the Observer window and respond YES to the confirmation prompt. It may take a while for the abort to happen. When it does, you will have to type METHOD DEFAULT in either Observer or ICL window to return to doing normal CCD runs. The ICL sesssion should see the abort and tidy up itself. Beware that ABORTS are not handled well by the underlying CCD controller.   You may in some cases get a system failure and have to to a "RESET HARD" to recover, although recent reports indicate it does normally work.

Another way of taking Charge Shuffling Observations

The Graphical User Interface runs on the Unix machine aatssz whereas the rest of the software runs on the VAX. In the event of a failure of the network communications between these machines it wouldn't be possible to use this method. It is possible to take charge shuffling data using the VAX alone. (see using the NS command and nodshuffle program).

Taking Charge Shuffling Data using the NS command and nodshuffle program

You shouldn't normally need to use this method, as the graphical user interface is a much easier way of starting charge shuffling runs. However, it may occasionally be useful in the event of a breakdown in network communications between the VAX and the Unis systems, as this method can be run entirely from the VAX.

In this mode a CSX file is generated using the program nodshuffle. See the "Generating CSX files"  section below.  When you do this there are two values output which you need to record as you will need them later. The items are

To run a nod and shuffle operation, you use the "NS" command at the ICL> prompt. This will prompt you for various values, being

TRUE/FALSE Is the run to be a bias RUN.  Defaults to FALSE.
CSX Filename
Here you specify the name of your charge shuffling description file.   See "Generating CSX files"  below.  The default location is  DISK$USER:[OBSERVER.CS_FILES] and the default file type is "CSX".
Timer Resolution
Used to determine the resoultion of the exposure and other timers in the CCD controller.  This is required as the range of the timers are much more limited then the range you may desire.  A common value here is "3", which indicates a resolution of 1 milli-second but limits you to an exposure plus an offset time of about 65 seconds. See "Generating CSX files" below.
External Delay
This is the amount of time the system must wait  for the external device (telescope to offset).  This value is given in terms of the timer resolution.  See "Generating CSX files" below
Cycle count
The number of observation cycles.  1 to 65535.
Use Axes
This should always be False for polarimetry runs.
RA Offset
        The RA offset - you have to specify this and dec offset even if the run does not involve nodding
Dec Offset
The Dec offset - One of the offsets must be non-zero or it will be rejected.
The window to use for reading out the detector. The system will save the existing window before specifying this one. IT will then restore the original window when the run is complete.
Finally, the system will output a summary and prompt you for confirmation. If you confirm, the run is started.  Note, it can take a while to start a charge shuffling run, but you should see messages every few seconds during this time.

Generating CSX files

CSX files can be generated from the graphical user interface by using the Save As... option.

It is also possible to generate CSX files using a program which runs on the VAX.   This program is run from the OBSERVER account using the NODSHUFFLE command.

Command options are

If specified, we are using the axes.
        Specifies a linear polarization run with four wave plate positions (0, 22.5, 45, 67.5)
        Specifies a polarization run with two wave plate positions (0, 45)
        Specifies a polarization run with two wave plate positions (22.5, 67.5)
        Specifies a circular polarization run with two wave plate positions
        Specifies a polarization/nodding run with two plate positions (0, 45) and two telescope positions
        Specifies a polarization/nodding run with two plate positions (22.5, 67.5) and two telescope positions
        Specifies a circular polarization/nodding run with two plate positions and two telescope positions
-offtime n
Specifies the offset time in seconds (real number)
-exptime n
Specifies the base exposure time in seconds (real number)
-offexptime n
Offset exposure time in seconds (real number)
Shutter time in seconds (real number)
-shift n
Rows to shift, (integer)
-output file
Specify output file. The default is standard output



Only one of the mode flags (axes,lpol,qpol,upol,cpol,qnod,unod,cnod) should be specified. If no mode is
specified offset mode is used.

The program writes to STDOUT the charge shuffling file.  It writes to STDERR the timer resolution index value and the external device delay value. For example, assume an axes mode operation, exposure time of 10 seconds in both positions, offset time of 2 seconds and shift of 300 rows.  The command is as follows

nodshuffle -axes -exptime 10 -offtime 2 -shift 300
This produces
The timer resolution value is "3"
The external device delay is "2000"
PR 0,65535,10000,12100,1,300,0,0,1
PR 0,65535,10000,12100,65535,300,0,0,2
PE 0,65535,1,2100,0,65535,0,0,1
PE 0,65535,1,100,0,65535,0,0,0
To catch the charge shuffling file in a disk file, you need to redirect STDOUT.  E.g
define/user_mode sys$output myfile.csx
nodshuffle -axes -exptime 10 -offtime 2 -shift 300
The timer resolution value is "3"
The external device delay is "2000"
And the file myfile.csx  which contains
PR 0,65535,10000,12100,1,300,0,0,1
PR 0,65535,10000,12100,65535,300,0,0,2
PE 0,65535,1,2100,0,65535,0,0,1
PE 0,65535,1,100,0,65535,0,0,0


The OBSERVER CCD software works as normal, and it is suggested that you first do a normal CCD GLANCE run to check the CCD system is working.

If the instrument sequencer task is not powered up or not communicating with the VAX, then you should expect the following just after entering the TDFNOD command

INSTSEQ initialising
!! No error to report (improper use of EMS)
!! OBEYW error from task INSTSEQ - action INITIALISE TAURUS_CCD
ADAMERR   %SYSTEM, device timeout
In Procedure: NS_LOAD
If you get this error, physically check the instrument sequencer micro. Ensure there are three lights down the left hand side (+5V, +12V and -12V). Ensure is is cabled correctly (see "Hardware Prepration" section). Hit the reset button.

Exit ICL and then start it again (you need only type ICL this time, although doing the full "TDFNOD 1" command does no harm)
If the system still does not start up then you may need to reset the terminal server (AAOD2Q) being used by the instrument sequencer before trying again. (Wait 20 seconds after power cycling the terminal server before trying again) In this case, you will also need to EXIT and restart the TELPOL_CONTROL program since it uses the same terminal server.


If the "Ready" string does not appear from TEL_CONTROL, then reset the terminal server (AAOD2Q) and go through the sequence described in the previous section for checking and restarting the instrument sequencer (since it uses the same terminal server) before restarting TEL_CONTROL

APPENDIX:  The difference between AXES and OFFSETS

AXES A/B mode requires that we specify positions at both extremes. We can push up to 0.63deg from centre to A, and centre to B, a total of 1.26deg.

OFFSET mode, you specify this directly in shuffle command. We can go as far as you like. For both AXES and OFFSET, we can only go 200"/s  even though the telescope can slew at 2700"/s. Why we can't use this slew rate baffles me.

Action sequence is as follows:

        expose 100s
        close shutter and slew (20s wait)
        expose 100s
        close shutter and slew (20s wait)...

        expose 100s
        close shutter and freeze autoguider (20s wait)
        slew (20s wait)
        expose 100s
        close shutter and slew (20s wait)
        thaw autoguider (20s wait)
        expose 100s

AXES is clearly operationally better than OFFSET since double wait time here. But we do need to determine half way position between object and sky to ensure that object sits in A, and sky in B.