http://hdl.handle.net/11422/15 2026-08-01T22:40:42Z http://hdl.handle.net/11422/29869 Title: Conexões planeta-estrela através do estudo das atmosferas de Jupíteres quentes Author(s)/Inventor(s): Navia, Micah Guimarães do Carmo Advisor: Ghezzi, Luan Abstract: In the last three decades, exoplanet research has advanced considerably, including the identification of a peculiar class known as hot Jupiters early in the first detections. These exo planets have radii and masses comparable to Jupiter’s but orbit their host stars in extremely short periods, with less than ten days. This proximity subjects them to intense stellar radiation, resulting in extremely high temperatures. The closeness to their stars suggests that radiation may significantly impact their atmospheres. To explore these effects, studies analyze data from secondary eclipses, which occur when the planet is occulted by its star. These observations allow the estimation of the atmospheres’ thermal emission, determining brightness temperatures in the infrared and detecting features such as thermal inversions, which represent changes in the temperature gradient as a function of atmospheric pressure. We used secondary eclipse data at mid-infrared wavelengths (3.6, 4.5, 5.8, and 8 µm, obtained by Spitzer) and near-infrared (J, H, and Ks), considering a sample of 95 hot Jupiters to test the hypothesis that planets without thermal inversions orbit active stars, while those with inversions orbit inactive stars. For this, we reproduced and updated two approaches from previous works that use secondary eclipse data in the 3.6 and 4.5 µm bands to classify the atmospheres of hot Jupiters. In this work, we expanded the analysis to all the bands mentioned above. Additionally, we performed various comparisons between stellar, planetary, and planet-star system parameters, separating the samples into exo planets with and without inversions. The results showed a significant correlation between the brightness temperatures in the H, 5.8 µm, and 8.0 µm bands and the chromospheric activity index log R′HK. We found that the distributions of exoplanets with and without inversion relative to log R′HK are statistically different (p < 0.05), as the distributions for the empirical index in the 3.6 - 4.5 µm color. Furthermore, we confirmed hypotheses from previous studies by observing the presence of thermal inversions in the most irradiated atmospheres and their absence in the less irradiated ones. Thus, we conclude that stellar radiation significantly influences the atmospheric properties of hot Jupiters and that thermal inversions may result from the complex interplay of multiple factors, including host star characteristics and specific planetary conditions. These results serve as an initial foundation for studying the atmospheres of rocky exoplanets, such as super-Earths. Publisher: Universidade Federal do Rio de Janeiro Type: Dissertação 2025-02-26T00:00:00Z http://hdl.handle.net/11422/29866 Title: Hiperbolicidade não uniforme para fluxos singulares e difeomorfismos Author(s)/Inventor(s): Mesquita, Gabriel Reis Machado de Advisor: Salgado, Luciana Silva Abstract: This work aims the study of some forms of weak hyperbolicity and some of their dynamical and ergodic properties, such as the relation between strong and weak hyperbolicity, dominated splittings and partial hyperbolicity, for differential dynamical systems (here understood as diffeomorphisms and flows from vector fields). In particular, we study the concepts of singular/sectional hyperbolicity and non-uniformly sectional hyperbolicity for singular flows. Publisher: Universidade Federal do Rio de Janeiro Type: Dissertação 2025-03-13T00:00:00Z http://hdl.handle.net/11422/29863 Title: The arithmetic and geometry of fibrations in rational and K3 surfaces Author(s)/Inventor(s): Meira, Felipe Zingali Advisor: Salgado, Cecília Abstract: This thesis consists of 3 chapters. The first chapter deals with introducing the main theory used in the subsequent chapters. Chapter 1 introduces basic concepts in the theory of elliptic surfaces, such as its main definition, the correspondence with elliptic curves over function fields and the classification of distinct fiber types. Furthermore, specific results on rational and K3 elliptic surfaces are presented. In Chapter 2, we study the rank of an elliptic curve E, defined over the function field k(T), which is given by a Weierstrass equation with coefficients of degree at most 2. This is done by studying the induced conic and elliptic fibrations on its Kodaira–Néron model R. In Chapter 3, we study K3 surfaces X with a non-symplectic automorphism σ ∈ Aut(X) of prime order. We classify distinct elliptic fibrations on X with respect to the action of σ on its respective fibers. Each type of elliptic fibrations is related to a linear system on the minimal resolution of the quocient ˜R = X/σ. When the action of σ on the Néron–Severi group of X fixes the fiber class of an elliptic fibration π, this method allows us to determine which Kodaira types are admissible as its reducible fibers. Furthermore, we are able to determine equations for its generic fiber. Publisher: Universidade Federal do Rio de Janeiro Type: Tese 2025-06-17T00:00:00Z http://hdl.handle.net/11422/29860 Title: An introduction to stochastic electrodynamics: motivations, foundations and applications Author(s)/Inventor(s): Silva, Nathália de Abreu Costa da Advisor: Souza, Carlos Farina de Abstract: This dissertation presents an introduction to Stochastic Electrodynamics (SED), a theory that seeks to reinterpret quantum phenomena based on classical principles, postulating the existence of a classical electromagnetic zero-point field (ZPF) with a Lorentz-invariant energy spectrum. The central motivation is to investigate whether this stochastic classical field can be the origin of effects traditionally associated with quantization. The work is divided into three main parts. First, we trace the historical origin of the concept of zero-point energy, from the crisis of classical physics in the face of the blackbody radiation problem – with contributions from Planck, Einstein, Stern, among others – to its initial formulation. Next, we discuss the formal foundations of SED, constructing the zero-point field from Maxwell’s equations and establishing its attributes of randomness, spectrum, and Lorentz invariance. Finally, we present some applications of the theory, focusing on its ability to derive Planck’s spectrum for blackbody radiation and to predict dispersive forces, such as the Casimir force, from classical interactions between matter and the ZPF. We conclude the dissertation by assessing the current scope, extensions, and limitations of SED, highlighting it as a fertile alternative theoretical framework for understanding quantum phenomena. Publisher: Universidade Federal do Rio de Janeiro Type: Dissertação 2026-03-05T00:00:00Z