Absolute Parameters and Apsidal Motion of the Eclipsing System V501 Mon

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: \({{T}_{1}} = 7380 \pm 60\) K, \({{M}_{1}} = 1.66 \pm 0.03{\kern 1pt} {{M}_{ \odot }}\), \({{R}_{1}} = 1.90 \pm 0.02{\kern 1pt} {{R}_{ \odot }}\), \({{T}_{2}} = 6920 \pm 30\) K, \({{M}_{2}} = 1.47 \pm 0.02{\kern 1pt} {{M}_{ \odot }}\), \({{R}_{2}} = 1.58 \pm 0.01{\kern 1pt} {{R}_{ \odot }}\). The photometric parallax determined in the study coincides with the Gaia value \(\pi =0.00103{''} \) within the error limits. For the first time, the apsidal motion rate \({{\dot {\omega }}_{{{\text{obs}}}}} = 0.022^\circ \)/year was accurately measured, which, within the error limits, matches the theoretical value: \({{\dot {\omega }}_{{{\text{theor}}}}} = 0.024^\circ \)/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. The main component is probably a pulsating variable star of the \(\delta \) Scuti type (DSCT).