Research

Speaker: Craig DeForest

The Polarimeter to UNify the Corona and Heliosphere is scheduled to launch in Spring 2025. PUNCH will image the outer corona and inner heliosphere to view them as elements of a single unified system, complementing the work of Parker Solar Probe. PUNCH science makes use of the physics of Thomson scattering to extract 3D information about the corona. This requires sensitive photometry and polarimetry, and merging of data from four separate cameras into a single “virtual focal plane”, which in turn drive rigorous treatment of the images from each camera, including corrections for distortion and PSF effects; I’ll give an overview of unusual aspects of the image calibration pipeline to address these needs. Further, PUNCH will report both “B” and “pB” (“polarized brightness”) — but that second term is somewhat ill-defined in the literature. I’ll describe the two major forms of pB currently in use, why PUNCH chose the more Stokes-like version, how PUNCH handles pB calculation and background subtraction, and an unexpected reason why three-polarizer coronagraphs give robust results. I will also highlight a surprising (to me) and helpful analogy between representations of linear polarization and of color, to further build intuition about polarimetry and its measurement.