Solar limb faculae: intensity contrast from two vantage points

Abstract

Small-scale magnetic flux concentrations contribute significantly to the brightness variations of the Sun, yet observing them - particularly their magnetic field - near the solar limb remains challenging. Solar Orbiter offers an unprecedented second vantage point for observing the Sun. When combined with observations from the perspective of Earth, this enables simultaneous dual-viewpoint measurements of these magnetic structures, thereby helping to mitigate observational limitations. Using such a dual-viewpoint geometry, we characterise the brightness contrast of faculae near the limb as a function of both their associated magnetic field strength and the observation angle. We analyse data from Polarimetric and Helioseismic Imager on board Solar Orbiter (SO/PHI), obtained during an observation program conducted in near-quadrature configuration with Earth, in combination with data from the Helioseismic and Magnetic Imager on the Solar Dynamics Observatory (SDO/HMI). The High Resolution Telescope of SO/PHI observed a facular region located near disc centre as seen from its vantage point, while the same region was simultaneously observed near the solar limb by SDO/HMI. We identify faculae and determine their magnetic field strength from the disc-centre observations, and combine these with continuum intensity measurements at the limb to derive dual-viewpoint contrast curves. We then compare these with contrast curves derived from SDO/HMI alone. Using two viewpoints, we consistently find higher facular contrast near the limb than from a single-viewpoint.

Accepted to Astronomy and Astrophysics

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