Main Objective: Coordinated observations with the Solar Orbiter (SO) Polarimetric and Helioseismic Imager (PHI) High-Resolution Telescope (HRT), close to SO perihelion in the second remote sensing window (RSW2) of the first orbit of SO Nominal Mission Phase (NMP) that will take place in early March 2022.
Scientific Justification: SO was successfully launched on Feb.10, 2020. All its onboard instruments are performing nominally and were commissioned during the early phase of the mission. Among them, SO/PHI provides maps of the vector magnetic field and line-of-sight velocities with two telescopes (Full Disk Telescope, FDT, and HRT).
One of the main scientific opportunities offered by SO is stereoscopic observation in conjunction with Earth- or near-Earth observatories. The difference in viewing angle bears important consequences on the possibility of comparing and merging such observations, as the optical path from the two viewpoints can be very different. In order to assess the general feasibility of stereoscopic observations, a thorough comparison of the spectropolarimetric properties of Hinode/SOT-SP and SO/PHI-HRT is necessary.
The SO/PHI-HRT calibration observation for this HOP will take place when SO is at 0.335AU, i.e. close to SO perihelion, where the HRT pixelsize will be 121km, while being at an angle of about 50.19deg longitude and 0.69deg latitude (on 2022-03-22T09:40:00) with Earth. The specific goal of these coordinated observations is to perform cross-calibrations between Hinode/SOT-SP and SO/PHI-HRT when the angular separation is relevant for stereoscopic observations, at the highest resolution of the current orbit.
In conjunction with the companion HOP gSolar Orbiter Polarimetric and Helioseismic Imager (SO/PHI) co-observationsh by D. Orozco, the observations provided by this HOP will attain cross calibration both at Earth-Sun line and at a finite separation angle with highest HRT resolution that will provide the quantitative foundations of all future investigations combining Hinode/SOT-SP and SO/PHI-HRT. The cross-calibration of SO/PHI-HRT has not been performed yet (a previous attempt was hampered by a procedural mistake in one of the SO instruments -not PHI). Since SO is already in the Nominal Mission Phase, the cross-calibration planned by the two companion HOPs is of utmost importance, and a top priority of the PHI instrument team.
The SO/PHI-HRT observations relevant to this proposal are planned as dedicated, PHI calibration observations, and are carried out by the PHI instrument team itself.