2002A&A...388..309L

Johnson BVRI photometric data for individual components of binary systems have been provided by ten Brummelaar et al. (2000AJ....119.2403T). This is essential because non-interacting binaries can be considered as two single stars and therefore play a critical role in testing and calibrating single-star stellar evolution sets of isochrones and the implicit theory. While they derived the effective temperature (T_eff) from their estimated spectral type, we infer metallicity-dependent T_eff from a minimizing method fitting the B-V, V-R and V-I colours. For this purpose, a grid of 621600 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. The BaSeL colours show a very good agreement with the BVRI metallicity-dependent empirical calibrations of Alonso et al. (1996A&A...313..873A), with the temperatures being different by 3±3% in the range 4000-8000K for dwarf stars. Before deriving the metallicity-dependent T_eff from the BaSeL models, we paid particular attention to the influence of reddening and stellar rotation. We inferred the reddening from two different methods: (i) the MExcessNg code v1.1 (Mendez & van Altena, 1998A&A...330..910M) and (ii) neutral hydrogen column density data. A comparison of both methods shows a good agreement for the sample located inside a local sphere of ∼500pc, 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 determinations provide effective temperature estimates for each component. They are in good agreement with previous spectroscopic determinations available for a few primary components, and with ten Brummelaar et al. below∼10000K. Nevertheless, we obtain an increasing disagreement with their temperatures beyond 10000 K. Finally, we provide a revised Hertzsprung-Russell diagram (HRD) for the systems with the more accurately determined temperatures.