Photometric versus empirical surface gravities of eclipsing binaries

Systematic differences in photometric stellar surface gravity determination are studied by means of the comparison with empirical values derived from detached double-lined eclipsing binaries. Photometric gravities were computed using Moon&Dworetsky (1985) grids based onKurucz (1979) atmosphere models, and empirical gravities were taken from Andersen (1991). Individual Strömgren colours and β indices of each component of the binary system have to be taken into account to correctly analyze the observed differences. A compilation of data on a sample containing 30 detached double-lined eclipsing binaries with accurate (≈ 1-2%) determination of mass and radius and availableuvbyHβ photometric data is also presented. Correction of the differences in terms ofTeff and log g for the range 11000 K < Teff < 20000 K reduces the mean residuals from 0.13 dex to 0.07 dex. For the range 7000 K < Teff < 8500 K, the consideration of metallicity effects by means of δm◦ index improves the accuracy from 0.20 dex to 0.09 dex.