Relation between Intensity Contrast and Magnetic Field for Active and Quiet Regions Observed on the Solar Photosphere

Recent high spatial resolution solar observations and simulations indicate that radiative properties of magnetic elements depend not only on their size and magnetic field intensity, but also on the properties of the plasma that surround them. Such simulations and observations are typically limited to a few line-of-sight variables. Some irradiance reconstruction techniques rely on the relation between magnetic field strength and intensity contrast to identify magnetic features and model their radiative contribution. Therefore, understanding the center-to-limb variation of these different radiative properties and, eventually, whether and how they change with the magnetic activity cycle can improve the capability to model solar irradiance. This study analyzes full-disk Helioseismic and Magnetic Imager (HMI) data products obtained at the 6173 Å spectral range to investigate the different radiative properties of magnetic features observed in active and quiet regions at various positions over the solar disk. In agreement with high spatial resolution observations and simulations, the study finds that, at all positions on the solar disk, magnetic elements located in quiet regions are characterized by higher photometric contrast than magnetic elements located in active regions and that these latter present negative contrast close to disk center.