Análise da deflexão gravitacional da luz em ocultações estelares

Abstract

This dissertation investigates the astrometric effects of the gravitational deflection of light during stellar occultations, with emphasis on the simultaneous contribution of multiple bodies in the Solar System. The main objective is to evaluate how these effects contribute to the apparent position of the occulting body under different occultation geometries and to what extent they may affect high-precision astrometric measurements. To this end, the relativistic model of Klioner, with microarcsecond-level accuracy, is employed, from which numerical routines are implemented to compute the deflection vectors associated with different massive bodies. The methodology combines theoretical analysis of the gravitational effect, computational implementation supported by the SORA package, and real case studies. Initially, the fundamental concepts of stellar occultations are presented, including how astrometric positions are determined and which factors constrain their accuracy, such as observation quality, number of chords, and temporal coverage of the event. The Klioner light-deflection model is then described, with emphasis on the specific expressions and approximations used in this work. Based on this, a computational approach is developed to adapt the model to the context of stellar occultations, allowing the evaluation of angular separations, deflection angles, and offsets in right ascension and declination, as well as the combined contribution of each massive body. Validation is carried out through a case study of the stellar occultation by Ganymede on 21 December 2020, which is used as a reference to analyze the behavior of the corrections arising from the proximity of the Sun, Jupiter, and Saturn at that moment. The results show that, although the gravitational deflection due to multiple bodies often remains below the positional uncertainties of many events, its magnitude is comparable to the precision achieved in the best recorded occultations, becoming significant when angular separations are small or when the event has a high signal-to-noise ratio. The analysis demonstrates that the event geometry, the alignment between the star, observer, and deflecting bodies, and the uncertainties in the ephemerides are decisive in determining the final magnitude of the correction. It is concluded that the systematic consideration of gravitational light deflection by multiple bodies improves the astrometric consistency of stellar occultations and may contribute to the refinement of reference frames, especially in future observational scenarios with higher instrumental precision.