Modelizacao de estrelas Be Classicas na regiao do infravermelho proximo observadas no levantamento APOGEE

Abstract

Massive stars are very complex objects and up to now their evolution is not well understood yet. Among the massive stars, the Classical Be stars are the subject of this dissertation. They are B-type, non-supergiants stars, whose spectra have, or had at some time, one or more Balmer lines in emission. These emission lines are formed in a circumstellar disk composed mainly by gas ejected from the central star. The disks of Classical Be stars are transient and the mechanisms responsible by the formation/dissipation of them are still poorly understood. In order to get a better understanding about these processes, as well as to determine the physical parameters of both, the central star and the disk, we use spectroscopic data obtained by the APOGEE-1 survey (SDSS-III) in the near IR (H band) for a sample of 63 stars and we have applied a large grid of models for Be stars using the code HDUST, called Be Atlas. The modeling of our sample was made using the code EMCEE based on Monte Carlo Markov Chain method. Thus, we present the results of this first application of Be Atlas for our sample of objects, which are promising. However, there are some important limitations as: 1) HDUST does not consider the electron scattering in its models ; 2) there is a restriction for models with mass M(star) > 7,5 M(sun) imposed by EMCEE giving to them a higher probability ; 3) the quality of APOGEE data reduction for many stars is questionable, due to calibration issues and possible persistence effects. Thus, the next steps of this work are the correction of all these problems and the expansion of the spectral coverage of Be Atlas to UV and optical bands, allowing us abetter determination ofthe physical parameters and a proper comparison with the literature. We will also analyze new APOGEE-2 data in order to identify new Be stars, expanding therefore our sample of objects.