Photometric study of the close binary system DD Monocerotis

New BV light curves of the short-period eclipsing binary system DD Mon have been obtained. Light-curve variability is seen in both B and V bands as compared with the light curves obtained in 1986 by Yamasaki et al. (1990). The light curves are analyzed by using Wilson-Devinney's synthetic light-curve program, and the present photometric solution reveals that DD Mon is a near-contact binary with the secondary component filling the Roche lobe. Combined with Yamasaki et al.'s (1990) spectroscopic results, absolute quantities of DD Mon are derived: mass of the primary M-1 = 1.05+/-0.08 M., mass of the secondary M-2 = 0.47+/-0.04 M., radius of the primary R-1 = 1.36+/-0.04 R., radius of the secondary R-2 = 1.03 +/- 0.03 R.. These results show that the components of DD Mon have evolved away from the ZAMS and through a mass-transfer process to the present semi-detached state. The variation in shape of the light curve may be caused by the evolution of the system and the activity of dark spots.