Resumo:
After almost 25 years of the discovery of the first trans-Neptunian object (TNO), besides Pluto, more than 1930 other objects were discovered at the outer solar system. The study of those bodies can provide precious information about the origin and chemical, dynamical, and thermal evolution of our planetary system. However, due to their large heliocentric distances, those objects are hard to observe directly without the aid of space telescopes and so only about 140 TNOs and Centaurs have their diameters, determined through infrared observations by Spitzer and Herschel space telescopes, and only about 16 have their densities known. To bypass the dificulties of direct observations, stellar occultation is one of the most precise and acurate technique to obtain information on the outer solar system objects. Sizes measurements to the order of kilometers, atmosphere pressures at nanobar levels and even ring systems can be detected with this technique. By using this method, about 10 TNOs had their diameter and albedo determined and it highlighted two Centaurs in the last years: Chariklo, that has a ring system discovered in 2013, and Chiron, that presents structures around the main body which is suspected to be rings, jets or a shell, discovered recently, and also it presented a cometary activity after its last passage to its perihelium. In order to prove the existence and orientation of the Chariklo's rings, determine which is the best explanation for the material around Chiron and search for other structures and putative satellites orbiting those bodies, those two centaurs were the targets chosen to be observed directly by using the Hubble Space Telescope, whose time proposal and its preliminary results are presented on this work. Also, a stellar occultation by a TNO named 2007 UK126, occurred in 2014, was observed by professional and amateur astronomers in several sites in the United States. By using small telescopes ($\sim$30 cm diameter) and video cameras, it was obtained 6 positive chords from which it was possible to obtain a diameter of 628 +34 -52 km and albedo $<$ 0,194 +0,018 -0,009 for the body. This work also presents in details the procedures for the reduction and analysis of this event.
