IRPOL
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Observers Please Note: Because IRPOL is not used very
often at UKIRT, at the start of a polarimetry run, users should check
that the waveplate is indeed rotating when requested to do so from
the acquisition software. Loss of control may NOT be apparent from the
control room,
though please ask the TSS to monitor IRPOL from the EPICS display (see
below).
Introduction
IRPOL is an Infra-Red Polarimetry facility, built by the University of Hertfordshire, which
at UKIRT provides imaging-polarimetry
with UIST or UFTI, coronographic
imaging-polarimetry with UIST, and spectro-polarimetry with UIST.
The IRPOL module is located above the telescope dichroic mirror
within ISU2 and consequently the
half-wave retarder (waveplate) is the first optical element in the
telescope beam after the primary and secondary mirrors, thereby
minimising instrumental polarisation.
The polarising analyser used with UFTI and UIST is a beam splitting
Wollaston prism; with UIST two prisms are installed, one in each grism
wheel, so that spectro-polarimetry is available with all grisms.
(Coronographic-)Imaging-polarimetry is likewise available with all imaging filters.
Specific Instrument Guides for Polarimetry
Guides specific to
UFTI imaging polarimetry,
UIST imaging polarimetry, and
UIST spectro-polarimetry
are available, as are the old guides to polarimetry with IRCAM/TUFTI and CGS4 (although these two
documents are no longer maintained). To make a printable version of
any of these pages click on the link at the top of the lilac side-bar.
These pages describe all you need to know to propose, prepare and
execute an observing run with IRPOL.
Optical Parameters of IRPOL2
Technical details and characteristics of IRPOL and its components
are available via the following links (all info. is contained on
one page):
IRPOL Trouble-shooting: Although problems
very rarely arise with the IRPOL module, here are a few tips - just
in case! (the old page is here...)
Polarimetric Standards
A list of polarized and unpolarized
standards taken from the literature is available.
UKIRT Observations of polarised and unpolarised standards, taken
with UIST and UFTI, have also been tabulated. We encourage all IRPOL
users to observe both polarised and unpolarised standards, and to
contribute to these tables! Please contact Chris Davis (c.davis at
jach.hawaii.edu) if you have results that may be of interest to other
users! A very basic cshell script is available for calculating the
percent polarisation and angle from the I, Q and U
images produced by the pipeline; simply enter the integrated counts
(from Gaia - aperture photometry):
calc-pol.prg
Polarimetry Data Reduction
Orac-DR pipeline recipes for imaging and spectropolarimetry are
now available. These are described in the individual instrument
guides (see above). Gaia, the tool used at UKIRT to display and
manipulate all imaging data, also now has a nice Polarimetry
toolbox option. Use this to plot polarisation vectors on top of
images of your target. Finally, the Starlink package Polpack
can be used to re-reduced both imaging and spectro-polarimetry
data. (A sample table file for updating UIST [and possibly UFTI)
header info with Polimp is given
here.)
The Starlink software suite can be downloaded from here:
http://starlink.jach.hawaii.edu/.
Starlink documentation is also now hosted by the JAC - for Polpack try:
http://docs.jach.hawaii.edu/star/sun223.htx/sun223.html.
Circular Polarimetry
Circular Polarimetry with UIST and UFTI is available to all UKIRT
users. Proposals are welcomed. However, the quaterwave plate and
additional hardware needed for circular polarimetry are owned by the
University of Hertfordshire, so collaboration with U. Herts is
requested. Contact Chris Davis (c.davis at jach.hawaii.edu) for
further details.
Contact Info./Acknowledgement
Chris Davis (c.davis at jach.hawaii.edu) is the
instrument scientist responsible for imaging and spectro-polarimetry
at UKIRT. All enquiries should be forwarded to him. Also, the UKIRT
and University of Hertfordshire would appreciate an acknowledgment in any
publication which contains data obtained using IRPOL.
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