Jhmj. Bruls et O. Von Der Luhe, Photospheric fine structure: An observational challenge - An analysis of radiative transfer effects on the visibility of small-scale structures, ASTRON ASTR, 366(1), 2001, pp. 281-293
The requirement on spatial resolution of a large solar telescope is frequen
tly based on the assumption that the smallest observable features in the so
lar photosphere could not be much different from a photon mean free path du
e to smoothing by radiative transfer. Although hydrodynamic simulations sho
w that much smaller structures should exist, a resolution of the order of 1
00 km is typically considered sufficient for observations in the photospher
e. We performed 2D non-LTE radiative transfer computations for thin flux sh
eets with widths ranging from 10 to 160 km in the solar photosphere. We dem
onstrate that such small structures - should they exist could be observed a
s small scale variations of intensity and polarization. We conclude that th
e size limit below which photospheric structure cannot be observed due to s
moothing: radiative transfer effects must lie well below 10 km. A spatial r
esolution limit for telescopes based on photon mean free path arguments sho
uld therefore be abandoned.