Properties of the binary star FS Monocerotis

From the analysis of the light curves and radial velocity curves, we have determined the masses and radii of the components: 1.631+/-0.012 M_sun_ and 2.051+/-0.012 R_sun_ for the primary component; 1.461+/-0.010 M_sun_ and 1.629+/-0.012 R_sun_ for the secondary component.

The formal uncertainties are all less than 1%. Based on our light curves as well as on the combined-light photometry of the system, we estimate effective temperatures of 6715+/-100 K for the primary and 6550+/-100 K for the secondary component, corresponding to spectral types of F2 and F4, respectively. Projected rotational velocities (v sin i) from the spectrograms are measured as 52+/-2 km.s^-1^ and 43+/-3 km.s^-1^, respectively, from the spectrograms and are consistent with rotation that is synchronous with the orbital motion.