PEPPER: Polarization-encoding differential photometer and polarimeter

PEPPER is a high-speed differential Polarization-Encoded Photometer and Polarimeter developed in the Center for Astronomical Adaptive Optics at the University of Arizona, Tucson, by Dr. Dan Potter and Matthew Graham. PEPPER is capable of acting as a high-speed polarimeter by using electro-optical switching to chop between standard star and target star, and between in and out-feature bandpass filter at frequencies fast enough to suppress atmospheric variations. PEPPER is capable of either high-speed polarimetry or differential photometry using a combination of simultaneous imaging and electro-optical switching. In the differential photometry mode, PEPPER utilizes the electro-optical switching to calibrate instrumental and atmospheric photometric variation. This technique coupled with a zero-read noise photon counting detector achieves photon noise limited results demonstrated to an accuracy of less than 1 part in 10 ⁵. Herein we present the design concept behind the photometer and the polarimeter mode of PEPPER, as well as, results from observations in the differential photometer mode at the Steward 90 inch telescope, at the Kitt Peak National Observatory, Tucson, Arizona. Results from the analysis of near IR polarimetry observations of young stars with circumstellar disks taken at the Gemini North Telescope with the Hokupa'a adaptive optics system are also presented.