V501 Mon UBVRI(RI)c light curves

Our photoelectric measurements over the past 30 years and a new solution of the radial velocity curve of the eclipsing star with an elliptical orbit V501 Mon (A8 + F2) allowed us to determine with high accuracy all the main parameters of the system: T1=7380+/-60K, M1=(1.66+/- 0.03)M_{sun}_, R1=(1.90+/-0.02)R_{sun}_, T2=6920+/-30K, M2=(1.47+/-0.02)M_{sun}_, R2=(1.58+/-0.01)R_{sun}_. The photometric parallax determined in the study coincides with the Gaia value 0.00103" within the error limits.

For the first time, the apsidal motion rate dw/dt_obs_=0.022deg/year was accurately measured, which, within the error limits, matches the theoretical value: dw/dt_theor_=0.024deg/year; 70% of this value is a relativistic contribution. The system possibly satisfies the condition of synchronism between rotational and orbital angular momenta. The age of the stars was determined to be 0.95 billion years.