An integral method for measuring solar limb darkening

Abstract

We suggest an integral method for recording the solar darkening function. The idea relies on using special properties of the filter based on the Fabry–Pérot interferometer (FPI). Specifically, a displacement of the FPI passband maximum is related to the angle of incidence of the light beam by a quadratic dependence. This means that for all inclined beams the transmission maximum is blue-shifted. The resulting spectral profile of the light transmitted by the FPI from the full disk can be represented as the sum of many FPI profiles shifted to the blue and with an amplitude of the maximum corresponding to the darkening function. The asymmetry of the resulting profile contains information about the darkening function and is the subject of measurement. By measuring the asymmetry variations, the authors are hopeful of measuring variations of the darkening function, including five-min oscillations.