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Description
We present a detailed analysis of the interesting W UMa binary FI Boo in view of the spectroscopic signature of a third body through photometry, period variation, and a thorough investigation of solution uniqueness. We obtained new BVR_c_I_c_ photometric data that, when combined with spectroscopic data, enable us to analyze the system FI Boo and determine its basic orbital and physical properties through PHOEBE, as well as the period variation by studying the times of the minima. This combined approach allows us to study the long-term period changes in the system for the first time in order to investigate the presence of a third body and to check extensively the solution uniqueness and the uncertainties of derived parameters. Our modeling indicates that FI Boo is a W-type moderate (f=50.15%+/-8.10%) overcontact binary with component masses of M_h_=0.40+/-0.05M_{sun}_ and M_c_=1.07+/-0.05M_{sun}_, temperatures of T_h_=5746+/-33K and T_c_=5420+/-56K, and a third body, which may play an important role in the formation and evolution. The results were tested by heuristic scanning and parameter kicking to provide the consistent and reliable set of parameters that was used to obtain the initial masses of the progenitors (1.71+/-0.10M_{sun}_ and 0.63+/-0.01M_{sun}_, respectively). We also investigated the evolutionary status of massive components with several sets of widely used isochrones.
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