Abstract
We present a detailed investigation of the low-amplitude contact binary HI Dra based on the new VRcIc CCD photometric light curves (LCs) combined with published radial velocity (RV) curves. Our completely covered LCs were analyzed using PHOEBE and revealed that HI Dra is an overcontact binary with low fill-out factor f = 24 ± 4(%) and temperature difference between the components of 330 K. Two spotted models are proposed to explain the LC asymmetry, between which the A subtype of W UMa type eclipsing systems, with a cool spot on the less massive and cooler component, proves to be more plausible on evolutionary grounds. The results and stability of the solutions were explored by heuristic scan and parameter perturbation to provide a consistent and reliable set of parameters and their errors. Our photometric modeling and RV curve solution give the following absolute parameters of the hot and cool components, respectively: Mh = 1.72 ± 0.08 and Mc = 0.43 ± 0.02 , Rh = 1.98 ± 0.03 and Rc = 1.08 ± 0.02 , and Lh = 9.6 ± 0.1 and Lc = 2.4 ± 0.1 . Based on these results the initial masses of the progenitors (1.11 ± 0.03 and 2.25 ± 0.07 , respectively) and a rough estimate of the age of the system of 2.4 Gyr are discussed.
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