Radial velocities of the F-type EB* V2154 Cygni

We use our observations together with existing uvby photometric measurements to derive accurate absolute masses and radii for the stars that are good to better than 1.5%. We obtain masses of M1=1.269+/-0.017M_{sun}_ and M2=0.7542+/-0.0059M_{sun}_, radii of R1=1.477+/-0.012R_{sun}_ and R2=0.7232+/-0.0091R_{sun}_, and effective temperatures of 6770+/-150K and 5020+/-150K for the primary and secondary stars, respectively.

Both components appear to have their rotations synchronized with the motion in the circular orbit. A comparison of the properties of the primary with current stellar evolution models gives good agreement for a metallicity of [Fe/H]=-0.17, which is consistent with photometric estimates, and an age of about 2.2Gyr. On the other hand, the K2 secondary is larger than predicted for its mass by about 4%.