GO Cyg BV light curves

Modelling of the system shows that the primary is filling Roche lobe and the secondary of the system is almost filling its Roche lobe. The physical parameters of the system are M_1_=3.0+/-0.2M_{sun}_, M_2_=1.3+/-0.1M_{sun}_, R_1_=2.50+/-0.12R_{sun}_, R_2_=1.75+/-0.09R_{sun}_, L_1_=64+/-9L_{sun}_, L_2_=4.9+/-0.7L_{sun}_, and a=5.5+/-0.3R_{sun}_.

Our results show that GO Cyg is the most massive system near contact binary (NCB). Analysis of times of the minima shows a sinusoidal variation with a period of 92.3+/-0.5-years due to a third body whose mass is less than 2.3M_{sun}_. Finally a period variation rate of -1.4x10^-9^d/yr has been determined using all available light curves.