Adding an RA/DEC Calibration to your Data

If you are using dual-beam data, the simplest method is probably to define the RA/DEC calibration once the $O$ and $E$ ray images have been extracted into separate images (i.e. after running POLKA). With single-beam data, you can define the RA/DEC calibration at any point. So, the procedure is:

• For dual-beam data, extract and align the $O$ and $E$ ray intensity images using POLKA. Specify the output images using parameters OUT_O and OUT_E, and give a null value (``!'') for parameter OUT_S since we will be using POLCAL to create the Stokes parameters later.

• Add an RA/DEC calibration to one of the aligned images created by POLKA (it doesn't really matter which one). This will usually require you to know the RA and DEC of at least two features in the image. See here for a simple description of how to use GAIA to do this.

• Create a cube of Stokes vectors using POLCAL. Any WCS information is copied from the first input image (given for parameter IN) to the output cube. For this reason, the first input image supplied to POLCAL for parameter IN should be the one containing the RA/DEC calibration created in the previous step.

• Continue to create a catalogue of polarization vectors as normal using POLVEC, POLBIN, etc.