P68-803: ESA SP2 Program

Imaging polarimetry requiring differential tracking.

This proposal includes both service observations on fixed dates (see schedule below) and ToO observations triggered on any date.

Instrument setup required for ALFOSC linear polarimetry

• Filter: R (#76)
• Aperture wheel: Calcite
• FAPOL: lambda/2

ToO triggers :

Scheduled service observations on fixed dates (date is the start of the night) :

Night        Target    UT Window    Duration   Comments (approx RA/DEC skyplane rates in "/h) 

06 Apr 2024  533671   23:00-05:00    1:00
12 Apr 2024  533671   22:00-05:00    1:00
19 Apr 2024  533671   21:00-05:00    1:00
26 Apr 2024    ?
02 May 2024    ?

Daytime and twilight calibration instructions:

• Biases are taken as part of the automatic calibration script alfosc-calibs in the morning

• NB! Afternoon dome-flats with the full polarimetry setup as follows (set off some afternoon time for this):
  1. In the Run-Selector, select the P68-803 Muinonen/Granvik program. This sets the fits header keywords and the data goes automatically to the right directory.
  2. power-on the telescope, place it and open mirror covers with the TCS commands alt 45 and o-m-c
  3. tcs.setup-tel-alfosc
  4. Place the halogen "FF lamp" under the telescope and plug in
  5. alfosc.carriage in
  6. alfosc.wheels -s Calcite -f 76
  7. alfosc.focus-offset
  8. alfosc.resetxy; alfosc.polwin; alfosc.bin 2
  9. Take a test exposure to determine the exptime t that gives between 300-400kADUs
  10. alfosc.linpolexpose 16 domeflat t 5 -nowindow; astrowakeup
  11. When finished, do alfosc.carriage out, alfosc.resetxy, and alfosc.allopen
  12. When setup is ready, reset focus: alfosc.focus-offset
  13. Close mirror covers and park the telescope with the TCS commands c-m-c and zenith
  14. In the dome disconnect the "FF lamp" and store it (NB! it can be hot!)
  15. If it takes more than about 1 hour before your evening observations start, do power-off on the TCS.

  The obserations above will make 5 cycles of 16 angles each with exptime t.

• ALFOSC twilight skyflats for filter R (#76) with 2x2 binning as follows: (because of 2x2 bin, take these as the last of the standard sequence of broad-band flats: u' U z' B V R r' g' i i').
  1. alfosc.wheels -f 76; focus-offset
  2. alfosc.resetxy
  3. alfosc.bin 2
  4. alfosc.easyflat 3

Observing instructions:

• If you are not already using ALFOSC, go to the desktop where the ALFOSC Sequencer is running, and change the telescope settings with the command:
    tcs.setup-tel-alfosc

• Go to the directory
    cd ~/scripts/68-803
  List the available scripts
    ls -lrt

  All OBs to be observed will have tonight's date (i.e. start of the night) in their name.
  Note that in addition to the target there can also be standard star polarimetry OBs

• Start the target script, when it tells you to do the pointing, go to another sequencer window and use either of these:

  tcs.asteph -n targetname
  tcs.asteph -m optimal-ll -n targetname (for fast targets, rates > 100"/h)
  tcs.asteph -m optimal-lr -n targetname (for fast targets, rates > 100"/h)

  these commands connect to JPL Horizon to get the actual position and the rates at this UT time.
  In the case of using the optimal modes you also get the best setting of the field-rotation to optimize guide star area for repositioning.
  You can use either of the two. Try first the one that involves less turning of the rotator. See examples below.

      
  > tcs.asteph -n 68548
  ...
  Your input target is                        -  68548
  Your observatory is Nordic Optical Telescope, La Palma.
  Retrieving data from JPL Horizons...
  Data retrieved successfully from JPL Horizons.
  The object being searched for is  68548_2001_XR31
  Prefix for file names will be  2023-Oct-04.68548_2001_XR31
  Today is  2023-10-04
  Your computer says time is  11:53  UTC.
  ***************************
  These tasks should be given to the TCS:
  ***************************
  tcs.append-object 68548_2001_XR31-1 17 06 18.91 +78 39 35.7 2000.0 0.0 0.0 17.314
  tcs.ag-off
  tcs.guide-object 68548_2001_XR31-1
  tcs.reposition-guide-probe 193.864 41.25260
  
  
  > tcs.asteph -m optimal-lr -n K07S06Q
  ...
  Your input target is                        -  K07S06Q
  Your observatory is Nordic Optical Telescope, La Palma.
  Retrieving data from JPL Horizons...
  Data retrieved successfully from JPL Horizons.
  The object being searched for is  2007_SQ6
  Prefix for file names will be  2023-Oct-06.2007_SQ6
  Today is  2023-10-06
  Your computer says time is  10:11  UTC.
  ***************************
  These tasks should be given to the TCS:
  ***************************
  tcs.append-object 2007_SQ6-1010 03 20 02.18 +09 15 10.5 2000.0 0.0 0.0 17.709
  tcs.ag-off
  tcs.tcs-command "instrument-name ALFOSC ALFOSC-LR"; tcs.guide-object -f 57.173 2007_SQ6-1010
  tcs.reposition-guide-probe 241.628 -374.546
  

• Copy and paste into the command line the last four lines listed by the script - one by one.
  
• If this is a fast target, by the time you have arrived, the target has already moved, and the FOV is small. It is a good idea to repeat the steps again from the tcs.asteph command.
  When you get the prompt back after the 4th command (which sets the differential RA/DEC rates), the guide star should be in the box,
  the box should be close to one edge of the TV screen, and the contrast value for guiding should be larger than 1.0. The star+box will move across the TV screen at the non-sidereal rates.
  Differential tracking AND guiding is now running.

• Press return in the sequencer window where the OB is runnning. This will start the data acquisition.

  If the target is fast, i.e. RA/DEC rates > 100"/h, then the guide star will reach the opposite end of the TV screen before the ~ 40 min long OB terminates.
  NB! You need to reposition before the guide star reaches the opposite edge!
  This is done by repeating the 4th command, tcs.reposition-guide-probe .... before the edge is reached!
  TCS warning beeps are given when there is 120, 90, and 60 seconds left.
  Ideally, the telescope is not moved while the guide probe is repositioned, but if many short exposures are used, it is wise to do this while the CCD is reading out.

  For more general information on how this works, see the section "Moving Targets" in the ALFOSC Cookbook.

At the end of the night:

• When all OBs are done (check also for standard star OBs with today's date ), please, close them.

• Most observations are scheduled service mode. Only in the case of ToOs/SoftToOs, please, fill in the ToO or SoftToO tracking log.

• Remember to run alfosc-calibs ALF*** in the morning, where the input parameter is the file prefix.

P68 tracking

Should any of the observations have been carried out using the OB system, you will find additional information HERE