Polarization patterns in the sky and their influence in astronomical observations

Beatriz Maria dos Santos Pereira

Key information

Authors:

Beatriz Maria dos Santos Pereira (Beatriz Maria dos Santos Pereira)

Supervisors:

Santiago González Gaitán (Santiago González Gaitán); Ana Maria Vergueiro Monteiro Cidade Mourão (Ana Maria Cidade Mourão)

Published in

November 30, 2022

Abstract

The perfect conditions of an astronomical observation assume a sky free of light contamination. However, this contamination is significant in astronomical observations in the visible spectrum and can be a source of systematic errors in polarimetric studies. The Moon is our study subject because it is the most important natural source of light contamination at night. To better comprehend the effects of light pollution on observations, we create a model allowing for a better understanding and estimation of the effect of moonlight sky polarization on polarimetric observations. We consider the Moon's radiation that arrives at the Earth's atmosphere, originally the Sun's radiation reflected by the Moon, passes through and collides with the atmospheric particles. This phenomenon leads to polarization patterns that depend mostly on the target's angular separation from the Moon. Depending on the localization of the observatory, time and conditions, the model estimates the sky polarization characteristics, optimizing the observation plans and simulating the scattering processes based on the light wavelength and the composition and density of the atmosphere. This study compares two analytical models: Rayleigh single scattering and multiple scattering model. With observations throughout two nights with FORS2 at ESO-VLT observatory in Paranal, we found the data has excellent compatibility with the Rayleigh model. However, the model fails outside optimal conditions and for longer wavelengths. We conclude that the multiple scattering model with corrections is necessary to achieve more accurate results. Other factors were also tested, such as the depolarization factor and the Sun's contribution during the twilight.