PULSAÇÕES E EMISSÃO EM ESTRELAS B

Abstract

This thesis investigated the variability of a set of B-type stars, using light curves from space telescopes Kepler and TESS. The analysis of 122 stars from the Kepler/K2 campaign 11 revealed a wide diversity of variability types, identifying 39 SPB (slowly pulsating B) stars, 53 objects with variability attributed to binarity and rotation, five Maia/FaRPB (Fast Rotating Pulsating B) stars, plus two cases of hybrid SPB/beta Cep pulsators and one beta Cep binary. Thirteen stars show SLF variability (stochastic low-frequency). Examining medium-resolution blue spectra from a subset of 45 stars enabled the spectral classification of these celestial objects and the determination of critical astrophysical parameters. Seismic analysis of 14 stars in our sample revealed a positive correlation between the dominant frequency f_g and the rotation frequency nu_rot. The analysis of TESS observations, for another group of stars, revealed intriguing correlations between photometric levels, circumstellar disk emission intensity, and non-radial pulsation frequencies for Be stars. Furthermore, the star HD 212044 investigation yielded a surprising result, revealing a negative correlation between photometry and the equivalent width of H alpha. The investigation of the star 28 Cyg, known for its contained behavior, revealed moderate increases in H alpha emission synchronized with non-radial pulsations and episodes of photometric brightness, enabling an understanding of the interactions between pulsations, mass ejection, and disk properties in Be stars. These results contribute to understanding the stellar variability, highlighting the need for future investigations to clarify specific questions, such as the true nature of the correlations observed in the star HD 212044. B Stars; Be Stars; Pulsations; Variability; TESS