High resolution polarimetry and the need for a large-aperture solar telescope

Recent advances in instrumentation and data analysis techniques resulted in almost diffraction-limited polarimetric observations at existing solar telescopes. In particular, adaptive optics combined with phase-diverse speckle imaging delivers diffraction-limited magnetograms over a field of view that is larger than the isoplanatic patch and over a period that is significantly longer than the short periods of excellent seeing. These observations show that the larger magnetic flux tubes in plages and the network can clearly be resolved, but that most flux in kG-field form is not resolved. The signal-to-noise ratio of these observations is insufficient to answer many pressing questions such as the existence of upwards traveling waves in the flux concentrations. Since the number of photons per diffraction-limited resolution element is a constant, independent of the telescope diameter and the distance of a resolved star, a large-aperture solar telescope is needed whose aperture is not so much determined by the diffraction limit but by the photon flux necessary to study various phenomena in the solar atmosphere.