Surface brightness-colour relations of dwarf stars from detached eclipsing binaries

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Aims. Surface brightness-colour relations (SBCRs) are useful tools for predicting the angular diameters of stars. They offer the possibility to calculate precise spectrophotometric distances based on the eclipsing binary method or the Baade–Wesselink method. Double-lined detached eclipsing binary stars (SB2 DEBs), with precisely known trigonometric parallaxes, allow us to calibrate SBCRs with a high level of precision. To improve such calibrations, it is important to supplement the sample of suitable eclipsing binaries with precisely determined physical parameters. Methods. We selected ten SB2 DEBs within 0.8 kpc of the Sun, which feature components of spectral types ranging from B9 to K3. We analysed their TESS and Kepler K2 space-based photometry simultaneously with the radial velocities derived from HARPS spectra using the Wilson–Devinney code. The disentangled spectra of DEBs were used to derive atmospheric parameters of their components by applying the GSSP code. The direct effective temperatures were also calculated using spectral energy distribution analysis. The O–C diagrams of the minima times were investigated to detect long-term period changes or apsidal motions. Results. Most of the systems are composed of significantly unequal components, with mass ratios as low as ~0.5. We derived precise masses, radii, and surface temperatures for them, along with their metallicities. The average precision of mass and radii determinations is 0.3% and 1.4%, respectively, for the surface temperature. The spectroscopic and photometric temperatures of the components are usually consistent to within 100 K, but in some systems, the difference is much larger. The components of HD 149946 show the highest difference (up to 400 K), while the atmospheric models favour different surface metallicities. We also provide an updated calibration of the equivalent width of the interstellar sodium D1 line and the reddening E(B–V).

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