Polarimetric Imager for Comets, PICO

Abstract

We constructed an imaging polarimeter, PICO, that was optimized for comets and/or cometary objects. PICO has a field-of-view of 5$' \times$ 10$'$ and employs a fixed Wollaston prism as an analyzer. In the case of polarimeters using a double-beam prism, such as a Wollaston prism, lateral chromatic aberrations originating from the prism often degrade the image quality and measurement accuracy. However, PICO suffers little lateral chromatic aberration due to compensation provided by newly designed lens systems that generate opposite lateral colors. Owing to this design, PICO can obtain highly resolved and very accurate polarization images throughout the FOV (field-of-view). The total accuracy is estimated to be $\Delta P \simeq [(P/8{5})^2 + 0.3^2]^{1/2}\;$% in polarization degree and $\theta \leq$ 3$^{\circ}$ in position angle; these values are satisfactory for cometary studies.