Characterizing and reducing the POL-2 instrumental polarization

Abstract

Sub-millimeter polarization observations using the POL-2 instrument mounted on the dual wavelength (850/450 μm) 10 k pixel sub-millimeter camera SCUBA-2 is in high demand on the James Clerk Maxwell Telescope (JCMT). The high level of Instrumental Polarization (IP) generated by the Gore-Tex^TM wind blind protecting the telescope is a hampering factor for these observations. The wind blind both introduces an overall linear polarization and a four lobed polarization footprint seen on strong point sources after removal of a beam averaged IP. During commissioning an IP model was developed for the 850 μm band but a good 450 μm model was lacking. This paper describes the effort to improve the 850 μm IP model, establish a 450 μm model and the work to understand and model the IP. During the work the wind blind was removed for a month to isolate the contribution of the wind blind from other sources of the IP. A theoretical model for the non wind blind generated IP has been developed. However, a theoretical model for the wind blind IP is still being worked on.