A revised HRD for individual components of binary systems from BaSeL BVRI synthetic photometry. Influence of interstellar extinction and stellar rotation

Abstract

Johnson BVRI photometric data for individual components of binary systems have been provided by ten Brummelaar et al. (2000). This is essential because such binaries could play a critical role in calibrating the single-star stellar evolution theory. While they derived the effective temperature from their estimated spectral type, we infer metallicity-dependent Teffs from a minimizing method fitting the B-V, V-R and V-I colours. For this purpose, a grid of 621,600 flux distributions were computed from the Basel Stellar Library (BaSeL 2.2) of model-atmosphere spectra, and their theoretical colours compared with the observed photometry. As a matter of fact, the BaSeL colours show a very good agreement with the BVRI metallicity-dependent empirical calibrations of Alonso et al. (1996), temperatures being different by 3+-3 % in the range 4000-8000 K for dwarf stars. Before deriving the metallicity-dependent Teff from the BaSeL models, we paid particular attention to the influence of reddening and stellar rotation. A comparison between the MExcess code and neutral hydrogen column density data shows a good agreement for the sample but we point out a few directions where the MExcess model overestimates the E(B-V) colour excess. Influence of stellar rotation on the BVRI colours can be neglected except for 5 stars with large vsini, the maximum effect on temperature being less than 5%. Our final results are in good agreement with previous spectroscopic determinations available for a few primary components, and with ten Brummelaar et al. below ~10,000 K. Nevertheless, we obtain an increasing disagreement with their Teffs beyond 10,000 K. Finally, we provide a revised Hertzsprung-Russell diagram for the systems with the more accurately determined temperatures. (Abridged)