Determination of physical parameters of B and Be stellar atmospheres

Abstract

The understanding of the physical laws that operate on the Sun and other stars enabled the development of an important segment of astrophysics known as "Stellar Atmospheres", in which one studies the physical and chemical properties of stellar photospheres, which represent the last mean free path taken by originating from nuclear reactions in the stellar core photons. Thus, all photons we observe the stars guard the "memory" of only this last stellar layer and allow us to just know directly the physical and chemical properties of this layer. Thus, a quick glimpse at the optical stellar spectrum can in principle provide important clues on the temperature, gravity, microturbulent velocity, metallicity, etc., relevant to the photosphere. These informations, when gathered for stars of different masses and stellar ages, serve as boundary conditions for the resolution of the differential equations that rule the physics of the stellar interior and allow for modeling of stellar interiors. Based on models of stellar interiors, astrophysicists are able to develop models of stellar populations, which serve as the foundation in understanding the dynamics of star birth in our galaxy as much as in distant galaxies. Thus, knowledge on the stellar photospheres is of paramount importance in astronomy and still has several open issues. In this research project we propose to study the physical and chemical conditions of the atmospheres of a group of stars of spectral type B and Be observed at the Laboratory National Astrophysics (MCT / LNA) and at the European Southern Observatory (ESO). The B stars have on average higher rates of rotation and consequently suffer geometric deformation, then assuming the shape of oblate spheroids and introducing an obscuration factor in the emerging spectra. (AU)