Abstract
Here we present the first CCD multi-color B, V and Ic light curves of the eclipsing binary stars TYC 3836-0854-1 and TYC 4157-0683-1, the data were obtained in four nights in the year 2010 and three nights in the year 2012 for the first one and in four nights in the year 2010 for the second one. Based on our data the short orbital periods of the systems are confirmed and revised to P=0.4155590days for TYC 3836-0854-1 and P=0.3960676days for TYC 4157-0683-1. Our observations of TYC 3836-0854-1 show symmetric light curves in all passbands with brightness in both maxima at the same level, while the light curve of TYC 4157-0683-1 appear to exhibit the typical O’Connell effect, with Maximum I brighter than Maximum II. By analyzing simultaneously the complete light curves with the 2003 version of the Wilson–Devinney code (2005 revision), photometric solutions were determined. Both the systems shows a small difference between the components temperatures of ΔT=14K for TYC 3836-0854-1 and ΔT =149K for TYC 4157-0683-1. The orbital inclination is i=78°.6 and i=79°.7 respectively. The systems are found to be a high fill-out, extreme mass ratio overcontact binary with a mass ratio of q = 0.206 and a fill-out factor of f=59.2% for TYC 3836-0854-1 and q=0.150 and a fill-out factor of f=76.3% for TYC 4157-0683-1, suggesting that both the systems are in the late stage of overcontact evolution.It is known that deep (f>50%), low-mass ratio (q<0.25) overcontact binary stars (DLMR) are a very important resource for understanding the phenomena of Blue Straggler/FK Com-type stars that is an unsolved problem in stellar astrophysics. One of the possible explanations for their formation is from the coalescence of W UMa-type overcontact binary systems. The absolute dimensions of both the systems are estimated from the logTeff - logL diagram and their dynamical evolution is inferred.
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