Stray-light effects on the solar intensity distribution

Abstract

A description of the stray-light problem based on a radiative transfer approach is presented. The two-dimensional convolution that describes the effect of the stray-light is recovered in this formalism. On the other hand, the normalization condition used for the spread function in our procedure is different from the one used in the old approach. The controversy raised by the old normalization condition is satisfactorily eliminated within our description. We have applied our formalism to aureole observations and derived the spread function parameters. These parameters are similar to the ones used in the standard approach but now a new quantity appears. It is derived consistently within our formalism and it allows a description of different atmospheric quality conditions without changing the actual shape of the spread function. This possibility is also a new characteristic of our formalism that has no analogy to the old one. Finally, the information derived from limb profiles is used to correct sunspot images. The correction does not need to make any assumption about the shape of the spot but it uses the information contained on the image itself. It is shown how, for large spots, the contamination of stray-light can be considered as an added constant level of light throughout the umbra.