DSpace Collection:

Conexões planeta-estrela através do estudo das atmosferas de Jupíteres quentes

Wed, 26 Feb 2025 00:00:00 GMT

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

Towards forecasting cosmological constraints from velocity angular power spectrum of type Ia supernovae

Thu, 27 Feb 2025 00:00:00 GMT

Title: Towards forecasting cosmological constraints from velocity angular power spectrum of type Ia supernovae Author(s)/Inventor(s): Bonifácio, João Pedro Monteiro Advisor: Gonçalves, Thiago Signorini Abstract: Galaxies’ peculiar velocities provide a powerful probe of cosmic structure growth through their correlations. However, measuring these velocities requires distance indicators. Type Ia supernovae (SNe Ia) serve as fundamental distance indicators due to their nature as standardizable candles, offering superior distance estimates compared to galaxy scaling relations, which have traditionally been used due to the limited number of detected SNe Ia. With the upcoming Rubin Observatory Legacy Survey of Space and Time (Rubin LSST) set to detect one million of SNe Ia, we have an opportunity to leverage them for peculiar velocity studies. Yet, current methods rely on 3D statistical estimators, which are ill-suited for Rubin LSST’s photometric data. Without a robust alternative, we risk failing to fully exploit Rubin LSST’s vast dataset for cosmic structure studies. To address this challenge, we investigate the application of angular power spectrum analysis to velocity fields. We examine the velocity-density field relationship, compute the velocity angular power spectrum, and compare it with existing literature. Due to computational challenges posed by highly oscillatory functions, we implement the Limber approximation—a calculation not previously applied to velocity fields. We find that while efficient at small angular scales, this approximation introduces significant errors at large scales, as expected. Additionally, we assess whether LSST’s large photometric sample could compensate for photometric redshift imprecision. Through the signal-to noise analysis, we demonstrate that precise redshift measurements are important to PV studies. This work represents a critical step toward enabling cosmological parameter forecasts using SNe Ia peculiar velocities in the Rubin LSST era. Publisher: Universidade Federal do Rio de Janeiro Type: Dissertação

Fotodestruição do benzeno em ambientes interestelares

Wed, 04 Apr 2007 00:00:00 GMT

Title: Fotodestruição do benzeno em ambientes interestelares Author(s)/Inventor(s): Neves, Rosicler da Silva Advisor: Boechat-Roberty, Heloísa Maria Abstract: The abundance of interstellar molecules depends on their dissociation and destruction rate, and those depend on the photodissociation cross section which is function of the photon energy. We had experimentally study photoionization and photodissociation processes of the benzene (C6H6), and the deuterated benzene (C6D6). Benzene is an essential intermediate in the formation pathways of polycyclic aromatic hydrocarbons (PAHs), which are thought to be responsible for unidentified infrared bands (UIR), observed in differents astronomical environments. The measurements were taken at the Brazilian Synchrotron Light Laboratory (LNLS), using soft X-ray and UV photons. The experimental set-up consists of a high vacuum chamber with a Time-Of-Flight Mass Spectrometer (TOF-MS). Kinetic energy distributions, abundances for each ionic fragment and dissociative and non-dissociative photoionization cross sections were determined by using PhotoElectron PhotoIon Coincidence techniques. We have observed that C6H6 is extremely resistant to UV photons, confirming that PAHs absorb the UV photons and after some internal energetic rearrangements, they can emit in the IR range. However, this molecule is destroyed by soft X-rays photons producing several ionic fragments. We also observed that C6D6 is more resistant than benzene. Stable doubly-charged species were observed. From the photodissociation and cross sections we have determined the photodissociation rate and the half-life of C6H6 and C6D6 in differents astrophysical environments. Publisher: Universidade Federal do Rio de Janeiro Type: Dissertação

Perturbações das equações de Einstein-Boltzmann e suas aplicações à radiação cósmica de fundo

Mon, 08 May 2006 00:00:00 GMT

Title: Perturbações das equações de Einstein-Boltzmann e suas aplicações à radiação cósmica de fundo Author(s)/Inventor(s): Barros, Gustavo de Advisor: Calvão, Maurício Ortiz Abstract: Study aimed at understanding the basics of the new and growing topic of cosmic microwave background (CMB) physics. We present the fundamental concepts, principles and results related with this problem. Since the relevant equations are essentially the Einstein-Boltzmann perturbed equations, a great part of this work is dedicated to these linearized equations, in the conformal Newtonian gauge, with vanishing tri-curvature, for scalar perturbations only. The initial conditions are also touched on. Another part of paramount importance is the application to the description of the power spectrum of temperature anisotropies. Publisher: Universidade Federal do Rio de Janeiro Type: Dissertação