Filtergraph Calibration for the Polarimetric and Helioseismic Imager

Abstract

Solar Orbiter mission will study the Sun to the proximity of 0.28 AU, reaching solar latitudes up to 34°. This spacecraft will be launched in 2017 and will represent a complete approach to heliophysics. The Polarimetric and Helioseismic Imager (PHI), on board of Solar Orbiter, will provide the most important data for helioseismology. PHI will measure the photospheric vector magnetic field and the line-of-sight velocity observing the FeI 6173 Å absorption line with a narrowband filtergraph (FG). At different spectral positions, the polarization state of the incoming light will be analyzed. The FG will provide a tuning range to compensate the spacecraft radial velocity and to scan the continuum at both sides of the absorption line. Thus, the fine tuning of the FG is essential for the instrument performance. Here we present the FG characterization and calibration status as they represent an important milestone in the development of the instrument.