Technique for accurate stellar polarimetry using CCD cameras

Using a technique for CCD polarimetry, we have obtained stellar polarization data with the 0.9-m telescope on Kitt Peak and with the Tek 2048 CCD camera. Measurements of stars viewed through holes in polarizing filters serve to correct for variations in atmospheric transparency. For the brightest stars the uncertainties in the measured polarization during a single, hour-long, polarimetric sequence are 0.3–0.5%, because of the residual effects of the variations in transparency. For fainter stars we are Poisson noise limited. Our technique provides some advantages over other techniques for CCD polarimetry, primarily because it can be easily integrated into existing photometric systems.