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).
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 minimizing 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are available, as are the old guides to polarimetry with IRCAM/TUFTI and CGS4 (although these two documents are no longer maintained).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):
- Prism Characteristics
- Waveplate Characteristics
- Focal Plane Masks
- EPICS control of IRPOL
- Finding Guide Stars with IRPOL
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! 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; simhereply 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.eao.hawaii.edu/.
Starlink documentation is also now hosted by the JAC – for Polpack try:http://docs.eao.hawaii.edu/star/sun223.htx/sun223.html.
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 required.
Tom Kerr should be the first point of contact for any proposed use of IRPOL at UKIRT. Also, the UKIRT and University of Hertfordshire would appreciate an acknowledgment in any publication which contains data obtained using IRPOL.