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Astron. Astrophys. 341, 857-866 (1999)

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4. Conclusion

The comprehensive knowledge of fundamental parameters of single stars is the basis of the modelling of star clusters and galaxies. Most fundamental stellar parameters of the individual components in SB2 eclipsing binaries are known with very high accuracy. Unfortunately, while masses and radii are well determined, the temperatures strongly depend on photometric calibrations. In this paper, we have used an empirically-calibrated grid of theoretical stellar spectra (BaSeL models) for simultaneously deriving homogeneous effective temperatures and metallicities from observed data. Although a few stars show an incompatibility between the observed and synthetic uvby colours if we try to match the three Strömgren indices (b-y), m1, and c1, the overall determinations are satisfying. Moreover, an acceptable solution is always possible when only considering two photometric indices, as in Case 1 or Case 2 (see Table 3). The large range of [FORMULA] associated with acceptable confidence levels makes it evident that the classical method to derive [FORMULA] from metallicity-independent calibrations should be considered with caution. We found that, even for hot stars for which we expect optical photometry to be nearly insensitive to the stellar metal-content, a change in the assumed metallicity can lead to a significant change in the predicted effective temperature range. Furthermore, for cool stars, both [FORMULA] and [FORMULA] can be estimated with good accuracy from the photometric method. The effects of surface gravity and interstellar reddening have also been carefully studied. In particular, an apparently minor error in reddening can change dramatically the shape of the confidence contour levels, and, therefore, the parameter values hence derived. By exploring the best [FORMULA]-fits to the photometric data, we have re-derived new reddening values for some stars (see Table 1). Finally, comparisons for 16 stars with Hipparcos-based [FORMULA] determinations show good agreement with the temperatures derived from the BaSeL models. The agreement is even excellent for the star having the most reliable Hipparcos data in the sample studied in this paper. These comparisons also demonstrate that, while originally calibrated in order to reproduce the broad-band (UBVRIJHKL) colours, the BaSeL models also provide reliable results for medium-band photometry such as the Strömgren photometry. This point gives a significant weight to the validity of the BaSeL library for synthetic photometry applications in general.

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© European Southern Observatory (ESO) 1999

Online publication: December 16, 1998