The Contrast of Magnetic Flux Concentrations at Near‐Infrared and Visible Wavelengths

Abstract

To reconcile discrepancies in the observed contrast of magnetic flux concentrations, we compute synthetic filtergrams from solar magnetoconvection models in four different passbands: two continuum bands, at 1626 and 575 nm, the G band, and the line wing of the Ca II K line. Magnetic flux concentrations are selected by their G-band brightness. In the near-infrared the selected flux concentrations appear inconspicuous with intensities that are on average below that of the synthetic average quiet Sun, while their contrast in the visible passband is mostly positive. When we account for limited telescope resolution and imperfect seeing, the contrasts of bright points in the visible become increasingly negative as a result of mixing with the dark intergranular lanes in which they are embedded. The correlation in bright-point intensity between different passbands becomes increasingly poor from the G band to the visible and the near-infrared. This is caused in part by the varying amount of spectral lines in each of the bands. Further, we find that the largest magnetic field concentrations, representative of micropores or magnetic knots, are dark in all four passbands. The brightenings in the Ca II K line wing do not coincide with magnetic flux concentrations on the spatial scale of the simulation. Finally, we find that the rms intensity contrast in all four passbands depends on the amount of magnetic field present in the simulation, with higher contrast for lower average magnetic field strength.