http://localhost:8080/tede/handle/tede/10 Wed, 13 May 2026 14:05:44 GMT 2026-05-13T14:05:44Z http://localhost:8080/tede/handle/tede/217 “ANÁLISES GERAIS DA VELOCIDADE DA LUZ COM OBSERVAÇÕES COSMOLÓGICAS” JAIANE DA SILVA SANTOS, JAIANE DA SILVA SANTOS Carlos André P. Bengaly Junior, Carlos André P. Bengaly Junior The fundamental constants of Nature play a crucial role in our understanding of the Universe. They represent the limits of our knowledge of the laws of physics, but at the same time, they systematize new phenomena yet to be discovered. In recent years, an enormous observational effort has been devoted to studying the possible variation in space and time of some of these fundamental constants. Such a discovery would have profound consequences for our current models of physical interactions and, in particular, for the theoretical framework behind gravitation. Cosmology provides us with a vast window to search for this variation, with scales of space and time ranging from the Solar System to the entire observable Universe and its origin. On the other hand, theoretical models are being actively developed in order to provide a physically viable description of the variation of fundamental constants. Therefore, measurements of fundamental physical constants using astronomical obser- vational data represent a powerful method to investigate evidence for new physics beyond the standard cosmological model, namely the ΛCDM model. In this context, we measure the speed of light c by means of the Hubble parameter and angular diameter distance measurements from current datasets, obtained from a compilation of galaxy ages and radial baryon acoustic oscillations (BAO) for the former, and Type Ia Supernova (SNe) distances from Pantheon+SH0ES for the latter. We do this by performing a Gaussian Process reconstruction of these quantities, in order to avoid the assumption of a cosmo- logical model. We then predict the accuracy of this measurement from upcoming galaxy redshift surveys, such as J-PAS, and from standard sirens from gravitational-wave exper- iments, such as LIGO and the Einstein Telescope. Our results indicate that we may be able to reduce the uncertainty of light speed measurements from approximately 5% with current data to 1.5-2% when these future data become available. Furthermore, we perform a test of the cosmic distance duality relation (CDDR), one of the most fundamental relations in Cosmology, in order to test a model of variable speed of light known as the “minimally extended varying speed of light" (meVSL). This model predicts that the speed of light varies together with other fundamental constants, in a way that preserves Lorentz invariance, thermodynamics, Bianchi identities, etc., but by modifying the duality relation mentioned above. We use different data sets of baryon acoustic oscillations from SDSS and DESI, as well as Type Ia supernovae from the Pantheon+SH0ES compilation, and Gaussian processes again to reconstruct the data of Supernovae luminosity distance. We obtained a deviation from the usual RDDC of approximately 4σ using Supernovae with a specific set of BAO data from the SDSS, which measures its transverse mode (2D). However, this result was not found in other BAO samples from the SDSS and DESI that measured its anisotropic mode (3D). This indicates to us that these data are not yet precise enough to distinguish between evidence for new physics and possible systematics errors. Observatorio Nacional Tese Fri, 20 Feb 2026 00:00:00 GMT http://localhost:8080/tede/handle/tede/217 2026-02-20T00:00:00Z http://localhost:8080/tede/handle/tede/216 “ESTUDO DE MODELOS DE GRAVIDADE MODIFICADA USANDO DADOS COSMOLÓGICOS DE AGLOMERAÇÃO DE MATÉRIA” Manoel Vicente de Souza Filho, Manoel Vicente de Souza Filho Armando Bartolome Bernui Leo , Armando Bartolome Bernui Leo The growth of cosmic structures is investigated through the analyses of f(z) and σ8(z) cosmic observables data, using non-parametric Gaussian Process reconstructions combined with MCMC statistical analyses. The standard flat-LCDM model, General Relativity–based extensions, and F(R) modified gravity scenarios are systematically compared in terms of statistical performance, physical consistency, and the level of tension in the S8 parameter relative to the Planck -2018 benchmark. Our results show that, while LCDM remains consistent with current data, it exhibits deviations at high redshifts. Among physically viable alternatives, the Hu–Sawicki (n = 1) model emerges as the most robust scenario, providing good agreement with observational data and compatibility with local gravity tests, while the Starobinsky (n = 2) model appears as a competitive alternative by moderately alleviating the S8 tension. Observatorio Nacional Dissertação Thu, 29 Jan 2026 00:00:00 GMT http://localhost:8080/tede/handle/tede/216 2026-01-29T00:00:00Z http://localhost:8080/tede/handle/tede/215 “ESTUDO DE PEQUENOS CORPOS DO SISTEMA SOLAR A PARTIR DAS OBSERVAÇÕES DO DARK ENERGY SURVEY E DE OCULTAÇÃO ESTELAR” Feliphe de Souza Ferreira, Feliphe de Souza Ferreira Julio Ignacio Bueno de Camargo, Julio Ignacio Bueno de Camargo Small bodies are considered collisional and dynamical remnants from the formation of the Solar System, carrying essential information about the initial conditions of the protoplanetary disk. Thus, the study of their different populations provides clues about their formation regions, allowing for a better understanding of the evolutionary processes that may have occurred. In this context, this thesis presents results from the study of different small-body populations using observational data from the Dark Energy Survey (DES) and the stellar occultation technique. Although not originally designed for Solar System astronomy, DES enabled the observation of over 399,000 objects, ranging from near-Earth asteroids to those located beyond Neptune’s orbit, using five optical filters. From their colors, we can obtain taxonomic information for asteroids, Centaurs, and trans-Neptunian objects to infer their surface physical properties and compare them with results from the literature. For the latter two groups, we seek possible correlations between their colors and orbital parameters. Using the stellar occultation technique, we estimated the size and 2D shape of the Jupiter Trojan (2207) Antenor, which was not observed by DES. Additionally, based on a positive detection in 2021, an intriguing feature of this small body was observed, which could be interpreted as either a large topographic anomaly or a possible binary object. We also present astrometric results for the studied Centaurs and TNOs, as well as for (2207) Antenor. Observatorio Nacional Tese Thu, 21 Aug 2025 00:00:00 GMT http://localhost:8080/tede/handle/tede/215 2025-08-21T00:00:00Z http://localhost:8080/tede/handle/tede/214 “Be Stars in Binary Systems” Danilo Ferreira da Rocha, Danilo Ferreira da Rocha Marcelo Emilio, Marcelo Emilio Be stars are fast-rotating B-type stars that display sometimes Balmer emission lines, especially Hα, produced in circumstellar decretion disks. In this thesis, we studied the role of binarity in these objects, aiming to determine their stellar and orbital parameters and to assess how companions affect disk dynamics, angular momentum, and variability. While rotation and non-radial pulsations are relevant, observational evidence shows that binary interaction is crucial for the Be phenomenon. To investigate this, we combined TESS photometry, BeSS/SOAR spectroscopy, and Gaia DR3 astrometry, applying frequency analysis, spectral modeling, and orbital solutions with Wilson–Devinney and MCMC methods. From our main sample list of 158 targets, we refined to 50 confirmed Be binaries, only two of which are eclipsing, while excluding non-Be binaries, non-binaries, and poorly observed systems. We found that the Be stars rotate at a large fraction of their critical velocity, with a range of values of v sin i/vcrit ≈ 0.30 − 0.85. The frequency analysis of TESS light curves revealed 3 dominant periodicities per target on average, and we identified harmonics up to the 5th order in one system. The Be stars exhibit relatively large effective temperatures and radii when compared to typical values observed for main-sequence stars. A highlight of this work is the system V1371 Tau, a hierarchical triple. For this system, we determined an eccentric inner orbit with Porb ∼ 34 days and e ∼ 0.27, and we detected a third body that significantly affects the dynamics. The system consists of a detached eclipsing B-type binary (B1V + B0V) orbited by a classical Be star (B0Ve). Photometric analysis reveals dominant low-frequency signals near 0.24–0.26 c/d, alongside higher-frequency signals attributed to non-radial pulsations of the Be star. Its projected rotation (v sin i ≈ 250 km s−1) corresponds to a critical rotation fraction between 0.44 and 0.76, substantially faster than the inner components (v sin i ∼ 160–200 km s−1). This study emphasizes the complexity of systems with Be stars and provides a basis for future research on their formation, evolution, and dynamics. Observatorio Nacional Tese Tue, 07 Oct 2025 00:00:00 GMT http://localhost:8080/tede/handle/tede/214 2025-10-07T00:00:00Z