PolarimetryObserversManual

Last-modified: 2021-05-21 (金) 22:41:03 (1071d)

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Observers' Manual for Polarimetry

How to carry out polarimetry observations
Notes for PLo, PTL
Revision history

How to carry out polarimetry observations †

Throughout this document we assume that you are logging into nicpc (160.128.0.40).

↑

Prepare for the normal observations †

See Observers' Manual

↑

Insert the polarisation plate (wavelength plate) †

Type the pol command on nicpc.
```
 nicpc% pol in
```
- For the case you need to retract the polarisation plate:
```
 nicpc% pol out
```
  (usually you do not need to do this while observing)

↑

Initialise the polarisation plate's position angle †

Type the pol command with initialisation option.
```
 nicpc% pol -init_rot
```
This makes the position angle (PA) to be at the mechanical origin.

↑

Test exposure †

Make sure that the shutter is at the 'open' position (otherwise open it by typing 'darkshutter-o').
Take the test image by, e.g., the following command.
```
 nicpc% TL 3 10 
```

↑

Adjust the pointing †

Choose one of the J, H and K band image, and make that band's image active on the DS9 window.

Display the polarisation window positions on the DS9 window.
```
nicpc% PolReg.sh 
```
Two green rectangles will be displayed, showing the positions of the two polarisation windows. Inside the left-side window, there will be a red square at the centre. We recommend to put the target at this position.

Put the target object on the red square with, e.g., the following command:
```
nicpc% xyoffset2 -p
```
click the current position of the target object, and then click the centre of the red square. (see also Observers' Manual)

↑

Insert the Wollaston prism into the light path. †

This process can be done interactively by using darkshutter.py command.
```
  nicpc% darkshutter.py -p
```

↑

Test exposure †

Take the test image to check if the target is properly put into the polarisation window.
```
  (example) nicpc% TL 3 10
```
If the target cannot be found near the centres of the polarisation windows, adjust the pointing with xyoffset2 command, etc.

↑

Focusing †

The focus is known to shuft by ~ +0.2 when inserting the Wollaston prism. Input the coarse value with focus command as a prior.
```
  nicpc% focus -5.20
```
Then run the autofocus command to further adjust the focus.
```
  nicpc% autofocus exp_time(sec) band(j/h/k) focus_start focus_end [num_sample]
```
- Make sure to specify which band to be used.
- focus_start must be smaller than the focus_end.
- If num_sample is omitted, the default value num_sample=5 is adopted.

↑

Do the observations †

Use the command PLo to carry out the polarimetry observations.
```
 nicpc% PLo mode exptime(sec) [object_name [num_frames_per_PA]]
 (例) PLo 3 120 HD114710 2
```
This command automatically rotates the polarisation plate, and take a set of images with four PAs. The definition of mode is similar to Lo/DL (see Observers' Manual).

↑

Self-guided observations †

You may want to detect your target with the fixed position of the detector as possible. ''gPLo" command can be used for this purpose. This command puts the telescope offsets to adjust the pointing everytime. In such case, follow the instruction below.

Move the target to the desired position on the detector, using xyoffset2, xyoffset3, etc.

nicpc% TL 3 2                      (Test exposure)
nicpc% xyoffset3 630 580  （-->Click the target on the DS9 window. Telescope moves so as to detect the target at X=630pix, Y=580pix)
nicpc% TL 3 2                      (Confirm with test exposure)

Do the polarimetry observations with gPLo command.
```
 nicpc% gPLo mode exptime(sec) object_name num_frames_per_PA band X Y
```
For example, if you fix the target at X=630pix, Y=580pix of the H-band image:
```
 nicpc% gPLo 43 20 Cyg_OB2_6 4 h 630 580
```

↑

Notes for PLo, PTL †

PTL is for test exposure, used when you do not like to save the data.
PLo is for usual polarimetry observations.
These commands automatically rotate the polarisation plate to PA=0/45/22.5/67.5 deg and take the images for each PA.

For example,

	PLo 3 10

gives a set of 12 frames listed below.

	/data/120504/rawdata/j120504_0001.fits     0 deg
	/data/120504/rawdata/h120504_0001.fits
	/data/120504/rawdata/k120504_0001.fits
	/data/120504/rawdata/j120504_0002.fits     45 deg
	/data/120504/rawdata/h120504_0002.fits
	/data/120504/rawdata/k120504_0002.fits
	/data/120504/rawdata/j120504_0003.fits     22.5 deg
	/data/120504/rawdata/h120504_0003.fits
	/data/120504/rawdata/k120504_0003.fits
	/data/120504/rawdata/j120504_0004.fits     67.5 deg
	/data/120504/rawdata/h120504_0004.fits
	/data/120504/rawdata/k120504_0004.fits

↑

Revision history †

2012.05.05 J.Takahashi: created
2012.05.16 J.Takahashi: reformatted to wiki, cited nic_observe.1205 by T.Zenno
2019.09.17 T.Saito: translated to English