Absolute parameters of the eclipsing binary V 821 Cas from UBVRI light curves and radial velocities . ⋆ †

We present UBVRI photometric measurements and spectroscopic observations of the double-lined eclipsing binary V821Cas. The radial velocities were obtained by means of the cross-correlation technique. Simultaneous analyses of the multi-band light curves and RVs give the absolute parameters for the stars as: M1=2.05±0.07 M⊙, M2=1.63±0.06 M⊙, R1=2.31±0.03 R⊙, R2=1.39±0.02 R⊙, Teff1=9400±400 K, and Teff2=8600±400K. Analysis of the O-C residuals yielded an apsidal motion in the binary at a rate of ω̇=0 ◦ .0149±0 ◦ .0023 cycle, corresponding to an apsidal period of U=118±19 yr. Subtracting the relativistic contribution we find that log k2obs=-2.590 which is in agreement with the value predicted by theoretical models. Comparison with current stellar evolution models gives an age of 5.6× 10 yr for the system.