The Polarimetric and Helioseismic Imager for Solar Orbiter: SO/PHI

Abstract

Abstract. The Solar Orbiter is the next solar physics mission of the European Space Agency, ESA, in collaboration with NASA, with a launch planned in 2018. The spacecraft is designed to approach the Sun to within 0.28 AU at perihelion of a highly eccentric orbit. The proximity with the Sun will also allow its observation at uniformly high resolution at EUV and visible wavelengths. Such observations are central for learning more about the magnetic coupling of the solar atmosphere. At a later phase in the mission the spacecraft will leave the ecliptic and study the enigmatic poles of the Sun from a heliographic latitude of up to 33• . A central instrument of Solar Orbiter is the Polarimetric and Helioseismic Imager, SO/PHI. It will do full Stokes imaging in the Landé g = 2.5 Fe I 617.3 nm line. It is composed of two telescopes, a full-disk telescope and a high-resolution telescope, that will allow observations at a resolution as high as 200 km on the solar surface. SO/PHI will also be the first solar polarimeter to leave the Sun-Earth line, opening up new possibilities, such as stereoscopic polarimetry (besides stereoscopic imaging of the photosphere and stereoscopic helioseismology). Finally, SO/PHI will have a unique view of the solar poles, allowing not just more precise and exact measurements of the polar field than possible so far, but also enabling us to follow the dynamics of individual magnetic features at high latitudes and to determine solar surface and sub-surface flows right up to the poles.In this paper an introduction to the science goals and the capabilities of SO/PHI will be given, as well as a brief overview of the instrument and of the current status of its development.

Prospects of Solar Magnetometry—From Ground and in Space

“…No space magnetograph has ever flown in such a difficult environment, with the spacecraft following a strongly elliptical trajectory, leading to significant thermal changes in the course of an orbit. The technical description below follows closely the more complete instrument descriptions by Gandorfer et al (2011) and Solanki et al (2015). For the sake of completeness and readability, we present a shortened version here.…”

“…Applying a high voltage across the crys- From Solanki et al (2015) tal allows changing the refractive index of the material and its thickness, and thus tuning the passband in wavelength across the spectral line. Gensemer & Farrant (2014) report on the fabrication technology for these etalons, whose absolute thickness, approximately 250 µm, is controlled to <10 nm, maintaining a thickness uniformity of <1 nm over the 60 mm aperture.…”

ADAHELI+: exploring the fast, dynamic Sun in the x-ray, optical, and near-infrared

“…FPIs have been selected, for their high performances, to be used in future large missions such as the James Webb Space Telescope, BepiColombo, and Solar Orbiter. [8][9][10] A wide operational spectral range is achieved due to the capacitance-stabilized piezoelectric control of the FPI 11 (which is, in that case, often referred to as CSE-FPI: capacitance-stabilized etalon-FPI) and suitable cameras.…”

Development and qualification of the Feed-Select Mechanism for the Polarimetric and Helioseismic Imager on-board Solar Orbiter

“…One of the key aspects of the Solar Orbiter mission is the combination of remotesensing instruments, observing the Sun's surface and atmosphere, with in-situ instruments performing particle, wave and field measurements in the vicinity of the S/C. The Polarimetric and Helioseismic Imager (SO/PHI) will provide maps of the magnetic vector and of the line-of-sight velocities in the solar photosphere [1,8]. It will thus probe the deepest layers of the Sun of all the instruments on-board Solar Orbiter.…”