The eclipsing binary systems with δ Scuti component – I. KIC 10661783

We present a comprehensive study of the eclipsing binary system KIC 10661783. The analysis of the whole Kepler light curve, corrected for the binary effects, reveals a rich oscillation spectrum with 590 significant frequency peaks, 207 of which are independent. In addition to typical $\delta$ Sct frequencies, we find small-amplitude signals in the low-frequency range that, most probably, are a manifestation of gravity-mode pulsations. We perform binary-evolution computations for this system in order to find an acceptable model describing its current stage. Our models show that the binary KIC 10661783 was formed by a rapid, almost conservative, mass transfer that heavily affected the evolution of both components in the past. One of the most important effects of binary evolution is the enormous enrichment of the outer layers of the main component with helium. This fact profoundly influences the pulsational properties of $\delta$ Scuti star models. For the first time, we demonstrate the effect of binary evolution on pulsational instability. We construct pulsational models of the main component in order to account for the mode instability of the observed frequencies. Whereas the single-star evolution model is pulsational stable in the whole frequency range, its binary-evolution counterpart has unstable modes, both, in high and low-frequency range. However, to obtain instability in almost a whole range of the observed frequencies, the modification of the mean opacity at the depth corresponding to temperatures log T = 4.69 K and log T = 5.06 K was necessary.