Estudo dos Parâmetros Físicos de Estrelas Variáveis Azuis Luminosas

Abstract

Some evolved massive objects are poorly understood by science, like Luminous Blue Variables (LBVs), which are the main focus of this dissertation. These objects are mainly characterized by episodes of intense mass loss, not yet well physically explained, causing strong photometric and spectroscopic variations. In order to better understand these objects, the aim of our study is to map the different variations and also estimate the physical parameters of 6 LBVs and LBV candidates from Magellanic Clouds. Based on light curves, we could confirm that eruptions are occuring on 4 stars: LHA 115-S 52, LHA 120-S 96, LHA 120-S 116, and LHA 120-S 155. For two of them, S52 and S116, there is no citation in the literature about these current eruptions. For LHA 120-S 30 and LHA 120-S 61, which are LBV candidates, we found no evidence of eruptions, being their classification as LBV still doubtful. Based on the analysis of FEROS and UVES spectra, we could note that during the quiescence, the LBVs spectra present intense P Cygni profiles in the Balmer lines and, in some cases, also in the Fe ii lines. We also found the presence of forbidden lines in emission and absorptions of singly ionized elements (of low ionization potential), being identified too few lines of higher ionized elements in some stars. During the eruption, an increase occurs in the intensity of the absorption lines and a reduction of the P Cygni profiles and forbidden lines emission. We also derived the physical parameters of all objects using CMFGEN code, confirming the existence of the instability strip in the HR diagram, where the objects during the quiescence are. It is also possible to estimate the rotational velocity of S61 and S155, which are in agreement with the expected in the literature. We also perform a search for dusty circumstellar nebulae in these objects, confirming the existence of them for S61 and S155, but for the other stars we could not discard nor confirm the presence of them. In addition, S52 and S116 have showed, during their quiescence, P Cygni profiles with multiple absorption components, indicating the presence of expanding layers in the wind with variable velocities, as described in AG Car. Finally, we also discuss the nature of these objects, based on their positions in the HR diagram and on the several results of our study.