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)
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:
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.
define instseq_sif IRISTEST_SIF: TEL_CONTROLThe 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.
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$user:[observer.csx_files] directory. The window is taken from the default location but you can specify any window in any sub-directory with a full path name.
The last file sent to VAX is the one picked up by the nod-shuffle initiation
The Charge Shuffling user interface used to define nod-shuffle runs. There are two ways to nod on the sky: AXES or OFFSETS. The telescope needs to be tracking. The fundamental difference between the AXES and OFFSETS mode is given in the appendix below. You do not want to be using OFFSETS for large angle nods.
Here are tips for different observing modes:
A. For sky flats and flux standards, use OFFSETS mode with an offset of zero. The set up is shown in the upper right figure.
B. If you are doing diffuse H-alpha detection, which requires nodding over large angles, the most efficient way is to probably use AXES mode and turn off the guiding. The set up is shown in the upper left figure. In Sept/Oct 2001, we found that this was a good match to the maximum nod allowed in AXES mode, i.e. 1.26 deg. AXES position A is offset by +240mm to the S and W; AXES position B is offset by -240mm to the N and E. This messes up the RA, dec positions in the FITS headers. We recommend that the on-field RA, dec be editted into the log pages.
C. If you are using microslits with TAURUS++, you will need to use AXES mode so as to guide on the on-source position. The set up is shown in the lower figure. In typical observations, the angular distance moved is only a few arcseconds.
If the load software cannot find mitll_nodshuf, there should be an up-to-date copy at disk$user:[observer.windows]. 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
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).
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
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
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 300This produces
The timer resolution value is "3" The external device delay is "2000" PI 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 PTTo 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 300Produces
The timer resolution value is "3" The external device delay is "2000"And the file myfile.csx which contains
PI 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 PT
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
Loading INSTSEQ_DIR:INSTSEQ into INSTSEQ 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 At Statement: obeyw INSTSEQ INITIALISE TAURUS_CCD Called by: NS_MODULEINIT_G Called by: NS_MODULEINITIf 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.
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:
close shutter and slew (20s wait)
close shutter and slew (20s wait)...
close shutter and freeze autoguider (20s wait)
slew (20s wait)
close shutter and slew (20s wait)
thaw autoguider (20s wait)
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.