THE FIRST MULTICOLOUR PHOTOMETRY OF THE V840 LYR CONTACT BINARY STAR

Abstract

Light curves for the total-eclipsing binary system V840 Lyr in the V, Rc, and Ic bands are presented; these display the O'Connell effect. Analysis was performed with the Phoebe031a software revealing that V840 Lyr is a W-type contact binary with a degree of contact factor of f = 15.1 ± 5.6%, a mass ratio of q = 0.4509 ± 0.0705, an inclination of i = 86.7°, and a temperature difference of ΔT = 45 K. An asymmetry in the light curves was modeled assuming a cool spot located on the secondary star. The period changes of the system are examined by combining our recently found times of light minima together with those in the literature. Absolute parameters were obtained as M1 = 0.74M⊙, M2 = 0.34M⊙, R1 = 0.74RM⊙, and R2 = 0.51RM⊙ from our photometric solutions, using some empirical relations. The long-term period increase and the contact configuration indicate that V840 Lyr will evolve into a fill-out overcontact binary.