Photometric Study of Close Binary

The present thesis int roduces the normal light variation for eclipsing binaries, which is caused by eclipse、reflection effect、gravity darkening effect and limb darkening effect, and the dis turbance of light curve, which is caused by the pulsation of components、dark spots and hot spot on the surface of the close bina ries, discus ses the O'Connell effect in near contact and contact binaries and the light curve variation with time in contact binaries, and reviews the analysis methods of light curve-"correction" light curve method and light curve synthesis method. In this thesis, a photometric study of the short-period near contact binary DD Mon has been presented. Complete photometric BV light curves have been obtained with the 1m telescope at Yunnan Obs ervatory, and three new times of light minimum have been determined from our observations. Combing with the four times of light minimum determined from Yamasaki et al's (1990) observations, we derived the new ephemeris of DD Mon, which was used to compute the phase of our obs ervations. When comparing Yamasaki et al's light curve with our light curve, the maximum brightness of our light curves was fainter by 0. 03mag (B) and 0. 08mag (V), the minimum brightness was also fainter by 0. 08mag(B) and 0. 12mag (V), the O'Connell effect on our light curves was not found, and the disturbance between 0.25-0.36 on their light curve was shifted to 0.16-0.25. Yamasaki et al's observations and our observations have been analyzed by using W-D method, the conclusion is the following: (1) DD Mon is anear contact binary with the secondary component filling it's Roche lobe. (2) Our photomet rics olutions and Yamasaki et al's spectrosco picelements have been combined to obtain the obsolute values for the physical quantities of DD Mon: Mass of the primary M₁=1.05±0.08M⊙ Mass of the secondary M₂= 0.47± 0. 04M⊙ Radius of the primary R₁=1.36± 0.04R⊙ Radius of the secondary R₂= 1.03± 0.03R⊙ (3) The fainter Maximum and minimum brightness were caused by the decrease of the temperature of secondary compo nent.(4) The shift of the disturbance on the light curve may be caused by the moving of the dark spots on the secondary component.