Close binary systems in star-forming regions: KV Cyg, V435 Cyg, and V699 Cyg in the OB association Cyg OB1

We carried out photoelectric UBVR observations of three eclipsing systems i n the OB association Cyg OB1. The ephemerides of minima and the amplitudes of light variations in the observed bands are refined. We solve all light c urves of KV Cyg and V435 Cyg by Lavrov's method and determine their photome tric orbital elements. Absolute parameters of the components of KV Cyg are estimated by using standard relations between the fundamental stellar param eters. By applying the same procedure to V435 Cyg, we failed to obtain the expected parameters of its components. The light curve of V699 Cyg underwen t a significant change, and the question of its interpretation remains an o pen question. All three variables are probable members of the OB associatio n Cyg OB1. We obtained UBVR photometry for 78 stars in the region of the as sociation, 41 of which belong to Cyg OB1.