Estudo dos Parâmetros Físicos de Estrelas com o Fenômeno B[e] na Galáxia e nas Nuvens de Magalhães.

Abstract

Abstract The stars with the B[e] phenomenon are characterized by the presence in the optical spectrum of B-type stars of: intense Balmer emission lines; permitted emission lines of singly ionized metals, e.g., Fe II; and forbidden lines in emission, e.g., [Fe II] and [O I]; in addition, these objects also exhibit a strong excess in the near- and mid-IR, due to circumstellar dust. These spectral characteristics are associated to the circumstellar medium and not to the object itself. In addition, the objects that show the B[e] phenomenon can be classified into four different groups according to their evolutionary stages: i) intermediate mass pre-main sequence stars, or Herbig Ae/B[e]; ii) massive supergiant stars, or B[e] supergiants ; iii) compact planetary nebulae, or cPNB[e]; and iv) symbiotic stars, or SymB[e]. However, more than 50% of the objects with the phenomenon B[e] has the evolutionary stage not well known, being called of unclassified B[e] stars. Thus, in this thesis we decided to study of the stars with the B[e] phenomenon in the Galaxy and in the Magellanic Clouds and for this, our study is divided in two parts: In the first part we analyzed 12 B[e] stars and candidates (8 from the Galaxy, 2 from the Large Magellanic Cloud and 2 from the Small Magellanic Cloud). Based on the analysis of high-resolution spectra (FEROS) and photometric data, we confirmed the presence the B[e] phenomenon for 11 objects from our sample. Using different methods we derive the effective temperature, spectral type, luminosity class and interstellar extinction. In addition, based on the distances provided by Gaia Data Release 2 (Gaia DR2) we also obtain the bolometric magnitud, luminosities and radius. From the HR diagram we suggest their evolutionary stages and as a result, we identified B and B[e] supergiants, B[e] stars probably at the main sequence or close to its, end HAeB[e] candidates and A[e] stars in the main sequence or pre-main sequence. However, our most remarkable results were the identification of ARDB 54, as the third supergiant A[e] discovered (the first in the LMC), and LHA 115-N82 that based on their spectral characteristics and variations in the light curve can be an LBV (Luminous Blue Variables) impostor. The second part of this thesis is dedicated to the creation of a grid of models for the B[e] supergiants, with the HDUST radiative transfer code called SGBepAtlas. It consider a large parameters space, including both stellar (radius, effective temperature and luminosity) and circumstellar/wind gas (mass loss rate, wind velocity structure, ratio between the equatorial and polar mass loss rate and terminal velocity, and inclinations) and dust (grain type, size and density) parameters. The SGBepAtlas, reproduces the spectral energy distribution from the ultraviolet to the radio/millimeter and also the profiles of hydroden lines. In addition, they provide polarimetric measurements and also images in different wavelengths that will allow us to compute optical/IR interferometric observables, like visibilities and closure phases. In this thesis were created around ∼35000 models which correspond to ∼20% of the total models (174960) to be created based on the parameter space for the B[e] supergiants. In addition, we created codes that use the Monte Carlo Markov Chain method, in order to determine the best models for the observations. To test our codes, we take a random model of SGBepAtlas with known parameters and fit several observables (continuous, equivalent width and line profiles). In addition, we also model the SED, and the Hβ and Hα line profiles of the star Hen 3-938, a possible B[e] supergiant. In the first test we observed that the input parameters are very similar to the output parameters. In the second test, the Hβ and Hα line profiles were not well fit, a possible explanation for this, was that our grid considers only a mass-loss rate value, despite our results are very promising.