P52-012: Determination of the black hole spin in OJ 287

1) Instrument setup

• Aperture wheel : Calcite
• Lambda/2 retarder
• Filter : R-band filter #76

2) Connection to P52-028: Polarization Monitoring of VHE gamma-ray BL Lacs (PI E. Lindfors)

If observations of P52-028 are made during the same night, no additional calibrations (points 3 and 4 below) are needed, we can use the same calibration frames.

5) Observing instructions

Observations can be made when the seeing is better than 3 arcsec and at any sky transparency up to "thin clouds".

• If not already done, type tcs.setup-tel-alfosc
• In a sequencer window type cd ~/scripts/52-012/
• Type tcs.append-object OJ_287_off 08 54 52.3 +20 06 23 2000 0 0 0 This puts OJ 287 in the TCS catalogue.
• Type tcs.guide-object OJ_287_off The command points the telescope to the midpoint between OJ 287 and Star 10 (see the finding chart below), displays the finding chart and starts auto-guiding.
• Run the script oj-pol.script. This sets up ALFOSC for R-band polarimetry (if not already), and starts a sequence of exposures through 4 retarder plate positions.
• After the first exposure, check that the image corresponds to the green circle in the finding chart below, i.e. both images of OJ 287 and Star 10 are within the field of view.
  If target acquisition or the script fails and/or the object does not fit with the finding chart, interrupt with Ctrl-C, offset the telescope correspondingly, and continue in manual mode (see point 8 at the bottom of this page).
• When finished with all targets and standards, reset ALFOSC CCD and optics with carriage OUT, resetxy and allopen, focus-offset, and set remsave_off.

Finding chart :

12x12 arcmin, North is up and East is to the left. The green circle indicates the field of view of FAPOL.

6) Observing epochs

Below are the observing dates for this campaign. The observations can be made at any time within the time window indicated for each date.

7) High polarization standard

We will used the same standard star observations as P52-012. However, we would like to check the position angle calibration with another star. One observation near the beginning of the campaign is enough. Below are the instructions on how to do this observation:

• If not already done, tcs.setup-tel-alfosc
• In a sequencer window type cd ~obs/scripts/52-012/
• In this directory type tcs.append-object HD25433 04 06 08.07 +62 06 07.0 2000 0 0 0 to enter the standard star into current TCS catalogue.
• Enter FAPOL lambda/2 plate into the beam with: alfosc.carriage IN
• Setup ALFOSC for R-band polarimetry with: alfosc.wheels -s Calcite -f 76 -forceFASU
• Make sure the focus is adjusted: alfosc.focus-offset
• Defocus a bit since this is a bright star: tcs.focus-delta 200
• Set the remote file storage path with: alfosc.rempath /data/service/52/012/
• Switch on remote saving: alfosc.remsave_on
• Display the finding chart with the command: xv hd25443.gif
• Point to the target and start auto-guiding: tcs.guide-object HD25433
• Set the window size to default for imaging polarimetry: alfosc.polwin
• Start the sequence of exposures at 4 angles of the lambda/2 plate with the script:
  alfosc.linpolexpose 4 HD25433 1.0 1
  Note that you will see two horizontally displaced (by 15 arcsec) images of the same field as that shown in the finding chart.
• When finished, return to the correct focus tcs.focus-delta 0 and reset ALFOSC CCD and optics with carriage OUT, resetxy and allopen, focus-offset, and set remsave_off.

Finding chart	Visbility on 2015-12-10

8) Manual observations

• If not already done, tcs.setup-tel-alfosc
• In a sequencer window type cd ~obs/scripts/52-012/
• In this directory type tcs.append-object OJ_287_off 08 54 52.3 +20 06 23 2000 0 0 0 to enter OJ_287 into current TCS catalogue.
• Enter FAPOL lambda/2 plate into the beam with: alfosc.carriage IN
• Setup ALFOSC for R-band polarimetry with: alfosc.wheels -s Calcite -f 76 -forceFASU
• Make sure the focus is adjusted: alfosc.focus-offset
• Set the remote file storage path with: alfosc.rempath /data/service/52/012/
• Switch on remote saving: alfosc.remsave_on
• Display the finding chart with the command: xv oj287_map_OFF.jpg
• Point to the target and start auto-guiding: tcs.guide-object OJ_287_off
• Set the window size to default for imaging polarimetry: alfosc.polwin
• Start the sequence of exposures at 4 angles of the lambda/2 plate with the script:
  alfosc.linpolexpose 4 OJ_287 15.0 1
  
• When finished with all targets and standards, reset ALFOSC CCD and optics with carriage OUT, resetxy and allopen, focus-offset, and set remsave_off.