New BVR photometric observations and light curve analysis of eclipsing binary V700 Cyg

Abstract

New CCD observations of eclipsing binary V700 Cyg were carried out in BVR filters during two nights in August 2017. Using the Binary Maker 3.0 and PHOEBE 0.31a softwares, the BVR light curves were analyzed and absolute parameters were determined. Our solutions show that the V700 Cyg is a W-type contact binary with mass ratio of q=0.54 and the degree of overcontact is f=17.9%. The asymmetric light curves in the maxima are explained by one cool spot on the secondary component. The positions of both components of V700 Cyg are shown in H-R and M-L diagrams, which indicate that the more massive component may be evolved main sequence star. The orbital period of eclipsing binary V700 Cyg was analyzed based on all times of minima from 1994 to 2017 (including new eclipse times). Analysis of the O–C curve shows that the orbital period of V700 Cyg is decreasing at a rate of dP/dt=−1.39×10−7dyr−1. This decreasing period can be interpreted by mass transfer from the more massive component to the less massive one. The cyclic variation in the O–C curve is probably due to the existence of a third body in the system with a period of 12.6 years and it can be probably a red dwarf.