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LIRIS Spectropolarimetry

Spectropolarimetry works essentially as normal LIRIS spectroscopy, and all the grisms used for normal spectroscopy are available in spectropolarimetry mode as well. The only restriction for spectropolarimetry is that a slit of width 0.75" has to be used.  

LIRIS displays four polarisation angles of 0, 45, 90, and 135 degrees simultaneously. For this purpose, the field of view is truncated to 4' x 1'.

Switch LIRIS into polarimetry mode using:

SYS> lspecpol <grism> <slit>

You then get four spectral slices simultaneously in one exposure, corresponding to polarisation angles of 45, 135, 0, and 90 degrees, respectively, counted from the top to the bottom of the image [to be confirmed!]. Any other polarisation angles can be achieved by means of instrument rotation.

The script used for observing, once the target has been normally acquired in the special spectropolarimetric slit, is the usual  ag_spec_nod. However, since the spectropolarimetric slit is only 50" long, you may want to decrease the value of the offset from the default of 12" in the  ag_spec_nod observing script.

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Contact:  (LIRIS Instrument Specialist)
Last modified: 10 September 2018