Polarization Switched Observations

The polarimeter is controlled by a number of keywords. It is normally kept out of line, but can be moved into the telescope's optically axis by entering the keyword POLIN. When this keyword is entered, the TEK4023 keyboard locks up for approximately 75 seconds, during which time the polarimeter moves into place. (The polarimeter power supply must be plugged in on the platform rack prior to typing POLIN .) By typing the keyword POLOUT, the polarimeter is moved out of the optical axis. Once again, the TEK4023 keyboard locks up for 75 seconds, and additional commands cannot be entered during this time.

Once in line, the polarimeter can be commanded to a specific position angle by typing POLANGLE xx, where xx is the angle in degrees. If desired, the polarimeter can switch between two position angles through the use of the keyword POLSWITCH. The options available are:

POLSWITCH 0

End polarization switching.

POLSWITCH 1

Switch g/2 plate angle between H (parallactic angle) and H + 25 . Thereby switching the polarization sensitivity between north and east (to obtain Stokes parameter Q).

POLSWITCH 2

Switch between H + 22.5 and H + 67.5 (northeast) and southeast; to obtain Stokes parameter U).

POLSWITCH 3

Same as POLSWITCH 1, except that a bias defined by the POLANGLE keyword is added to both positions.

POLSWITCH 4

Same as POLSWITCH 2, except that a bias defined by the POLANGLE keyword is added to both positions.

It is important to type POLSWITCH 0 when through with polarization switching, and it is your responsibility to type POLOUT when all polarimeter mode observing is completed. It is wise to visually check the polarimeter position and once out of the beam, to unplug the polarimeter power.