Fundamental atmospheric parameters of B stars in the Alpha persei open cluster = Paramètres atmosphériques fondamentaux des étoiles B dans l'amas ouverts Alpha persée

Abstract

It is important to understand stellar evolution as well as the chemical composition and structure of the Galactic disk, in which B stars in open clusters play a major role as they are of the most massive and brightest objects in these clusters. The fundamental atmospheric parameters (Teff, log g) of the B stars in the Alpha Persei open cluster (190pc, 50Myrs) have been determined using the Stromgren uvby-β photometric system, with a calibration technique by Napiwotzki et al. (1993)[65]. The method is based on fitting spectral lines of fundamental stars to synthetic spectra based on Kurucz (1979)[46] LTE model atmospheres. An echelle spectrum of one of the cluster’s B stars has been obtained and reduced, however without being used for analysis due to its low S/N quality and technical difficulties. Comparison between the determined parameters for our sample B stars to those obtained by previous work, allows us to put constraints on the photometric versus spectroscopic methods used to calculate the fundamental parameters of stars. Specifically, the case of emission-lines B stars and fast rotating stars (υsin I ≥ 200Km/s) whose color indices and Hβ absorption lines can be contaminated by emission, as well giants and binaries whose thin atmospheres (relative to the stars radii) cannot simply modeled using LTE’s plane parallel and spherical symmetry due to the presence of convection and mixing processes, as well as mass losses in their atmospheres.