Instrument Science Report WFPC2 97-11:
WFPC2 Polarization Calibration
J. Biretta and M. McMaster
December 23, 1997
We derive a detailed calibration for WFPC2 polarization data which is accurate to about 1.5%. We begin by computing polarizer flats, and show how they are applied to data. A physical model for the polarization effects of the WFPC2 optics is then created using Mueller matricies. This model includes corrections for the instrumental polarization (diattenuation and phase retardance) of the pick-off mirror, as well as the high cross-polarization transmission of the polarizer filter. We compare this model against the on-orbit observations of polarization calibrators, and show it predicts relative counts in the different polarizer/aperture settings to 1.5% RMS accuracy. We then show how this model can be used to calibrate GO data, and present two WWW tools which allow observers to easily calibrate their data. Detailed examples are given illustrationg the calibration and display of WFPC2 polarization data. In closing we describe future plans and possible improvements.