Absolute dimensions of eclipsing binaries. I.

New radial velocities determined from high-dispersion coudé spectrograms and new uvby light curves have been analysed to yield accurate absolute dimensions of the double-lined B2 V eclipsing binary QX Car (HD 86118). The masses and radii have been determined to an accuracy of ≡1.5%. Absolute magnitudes and other relevant astrophysical parameters are also given. The orbital eccentricity is appreciable and previous photometry showed significant apsidal motion. Combining all the data, a well-determined period for the apsidal motion, U = 354 ± 4 yr and a density concentration coefficient log k₂ = -2.07 ± 0.05, are determined.