Predição de ocultações estelares por objetos troianos de Júpiter

Abstract

The solution of the restricted three-body problem, proposed by Lagrange, provides two regions of possible stable equilibrium, where smaller bodies can orbit a central body with a semi-major axis similar to that of a larger body. The bodies located in these regions are known as trojans. It has been shown that these objects, especially the Trojans of the planet Jupiter, are important pieces in the formation and dynamic evolution of the Solar System. Several models of dynamic evolution have been developed in recent years, with the Jumping Jupiter Nice model being largely accepted by the scientific community. This model claims that the Trojans were formed in the Kuiper belt region and, during the migration of the orbits of the giant planets, they were captured in those equilibrium regions. Currently, there are more than seven thousand Trojans with determined orbits, but there is little information on the physical properties of these bodies. In order to derive their physical properties very accurately, the use of the stellar occultation technique is proposed. This method consists of recording the apparent blockage of a star’s light when a body of the solar system is interposed between the star and the observer. Stellar occultations allow the determination of object sizes and shapes with accuracy in the order of the kilometer, and consequently the determination of other physical parameters such as albedo and density with great precision. In addition, it is possible to verify the existence of rings, satellites and atmosphere in these small bodies. In order to observe an occultation, it is necessary to predict when and where this event will occur. In this procedure the positions of the object and of the star are compared over time, which requires good ephemerides of the object and good position of the stars. At present, the positions of the stars are obtained from the second version of the Gaia catalog, which has precisions in the order of the milliarcsecond (mas), yet the ephemerides have imprecision that can reach a hundred mas, what is much larger than the apparent dimension of the object itself. To improve the ephemeris it is necessary to add new positions of the bodies, for a new adjustment of orbit, difficult task due to the low brightness of these objects. For this reason, it is proposed the use observations from images randomly obtained by large surveys. In this work, the search and selection of Trojan objects was done from the observational database of the Dark Energy Survey (DES). From these observations, new positions were obtained, which were used to improve the object’s ephemerides. Filtering DES observations, and including the main known objects, a total of 54 Jupiter Trojans were selected. A tool was developed to predict stellar occultations, with which approximately fortyone thousand events were obtained in the interval from March 2018 to December 2020. These predictions are made available on websites and software for the diffusion and realization of observational campaigns. It is worth mentioning that two events involving two Trojans, Leucus and Ennomos, have been already detected by collaborators of the group.