Spectropolarimetry works essentially as normal LIRIS spectroscopy
, and all the grisms
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
. 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.