Absolute Dimensions of the A-Type Eclipsing Binary V364 Lacertae

We present photoelectric observations in B and V , as well as spectroscopic observations of the 7.3 day period double-lined eclipsing binary V364 Lacertae. From the analysis of the light curves and the radial velocity curves we have determined the absolute dimensions of the components with high precision (≲1%). The masses for the primary and secondary are M A = 2.333 ± 0.015 M ⊙ and M B = 2.296 ± 0.025 M ⊙ , respectively, and the radii are R A = 3.307 ± 0.038 R ⊙ and R B = 2.985 ± 0.035 R ⊙ . We derive also effective temperatures of T = 8250 ± 150 K and T = 8500 ± 150 K, and projected rotational velocities of v A sin i = 45 ± 1 km s -1 and v B sin i = 15 ± 1 km s -1 . Evolutionary tracks from current stellar evolution models are in good agreement with the observations for a system age of log t = 8.792 (6.2 × 10 8 yr) and for solar metallicity. Hints of a lower metallicity from spectroscopy and photometry appear to be ruled out by these models, but a definitive comparison must await a more accurate spectroscopic abundance determination. Analysis of all available eclipse timings along with our radial velocities of this moderately eccentric system ( e = 0.2873 ± 0.0014) has revealed a small but significant motion of the line of apsides of = 0.00258 ± 0.00033 deg cycle -1 , corresponding to an apsidal period of U = 2810 ± 360 yr. The contribution from general relativity effects is significant (∼17%). A comparison with predictions from interior structure models shows the real stars to be less concentrated in mass than expected. Our measurements of the projected rotational velocities indicate that the primary star is essentially pseudosynchronized (synchronized at periastron), while the secondary is spinning 3 times more slowly and is not yet synchronized. Both the rotational status of the stars and the nonzero eccentricity of the orbit are consistent with the predictions from tidal theory, specifically for the radiative damping mechanism.