2005AJ....129.2798W

New differential UBV photoelectric photometry and echelle spectroscopy for the eclipsing binary AR Mon are presented. A total of 46 radial velocities for each component are obtained using the TODCOR procedure. We solve the new and previously published multicolor light curves simultaneously with the new radial velocities using the latest version of the Wilson-Devinney program. We confirm that AR Mon is a semidetached binary consisting of two evolved giant stars and is a member of the rare class of ``cool Algols.'' The size of the primary, more massive component is about (1)/(3) that of its limiting lobe, and the secondary star is a lobe filler. We present two solutions, one without third light, the other including amounts of third light of 8% in V, 6% in B, and 5% in U. We determine magnitudes and colors for AR Mon's two components, as well as for the third star. If real, the latter is estimated to be a dwarf foreground star. The mass and radius of the primary (2.480±0.014M_☉, 8.002±0.089R_☉) place the star very close to the evolutionary track of a 2.5M_☉single star of solar chemical composition, indicating that the star may have adjusted its structure to mass gained from its companion. Synchronous rotation rates for both stars are in excellent agreement with vsini values determined from line profiles.