The Polarimetric and Helioseismic Imager on Solar Orbiter

Abstract

The Polarimetric and Helioseismic Imager on the Solar Orbiter mission (SO/PHI) is the first magnetograph and helioseismology instrument to observe the Sun from outside the Sun-Earth line. It is the key instrument meant to address the top-level science question: How does the solar dynamo work and drive connections between the Sun and the heliosphere? SO/PHI will also play an important role in answering the other top-level science questions of Solar Orbiter. It will provide valuable supporting observations for Parker Solar Probe. The instrument carries out narrow-band imaging spectro-polarimetry using a tunable LiNbO3 Fabry-Perot etalon, while the polarisation modulation is done with liquid crystal variable retarders (LCVRs). The line and the nearby continuum are sampled at six wavelength points and the data are recorded by a 2k x 2k CMOS detector. To save valuable telemetry, the raw data are reduced already on board, including being inverted under the assumption of a Milne-Eddington atmosphere. SO/PHI is composed of two telescopes, the Full Disc Telescope (FDT), covers the full solar disc at all phases of the orbit, while the High Resolution Telescope (HRT), can resolve structures as small as 200 km on the Sun at closest perihelion.

The standard data products of SO/PHI are maps of the photospheric magnetic field vector, line-of-sight velocity and continuum intensity with a highest cadence of one minute. The operational modes of SO/PHI are kept highly flexible allowing to adjust to the actual science goal chosen for a Solar Orbiter operation window.