Estudo espectroscópico, fotométrico e interferométrico de estrelas Be Clássicas

Abstract

Classical Be stars are defined as those stars whose spectrum has, or had for some time, one or more Balmer lines in emission. These stars show a transient gaseous circumstellar disk, whose formation process is still not well understood, but it may be related to some factors such as: high stellar rotation rate, close to the critical velocity, and the presence of non-radial pulsations. The main objective of this thesis is to estimate the physical parameters of the star and its circumstellar disk, for a sample of Be stars observed by the APOGEE survey and also by the FEROS spectrograph, and with photometric data from the literature. For this purpose, we used the BeAtlas grid of models, created with HDUST, a 3D radiative transfer code. The best models that reproduce the observables (hydrogen line profiles, Brackett 11 and 13, and Hα, and the spectral energy distribution) were chosen using the EMCEE code, based on the Monte Carlo Markov Chain method (MCMC). Given that the BeAtlas grid was developed for individual stars, a filtering of our initial sample was performed to remove confirmed and suspicious multiple stars, according to the literature. In addition, we also used the speckle interferometry technique to identify new binary and/or multiple systems. After filtering, our final star sample is formed by 102 stars. As a result, we obtained a set of physical parameters for each star (mass, luminosity, age, pole temperature, radius and gravity, oblateness, rotation velocity, parallax and extinction) and for their respective disk (density distribution and inclination), through the modelling of each observable. For most stars in our sample, these parameters were estimated for the first time. The determination of the final value for each parameter was obtained after a thoughtful analysis, taking into consideration the convergence of the modelling and the comparison with the literature. It is important to emphasize that the grid-model has its limitations, both with regard to the coverage of the space parameters and the absence of certain physical processes, such as line widening by electron scattering. Finally, I highlight the publications in which I have participated, especially an article of which I am the first author, which presents the discovery of three new double stars among Be stars, as well as four new companions in previously known multiple systems, using speckle interferometry.