KIC 6206751: the first R CMa-type eclipsing binary with γ Doradus pulsations

Jae Woo Lee1 and Jang-Ho Park1,2

1Korea Astronomy and Space Science Institute, Daejon 34055, Korea

2Department of Astronomy and Space Science, Chungbuk National University, Cheongju 28644, Korea

We present the absolute properties of the double-lined eclipsing binary KIC 6206751 exhibiting multiperiodic pulsations. The Kepler light curve of this system was simultaneously solved with the previously published radial-velocity data. The results indicate that the binary star is a short-period semi-detached system with fundamental parameters of M1=1.66±0.04 M⊙, M2=0.215±0.006 M⊙, R1=1.53±0.02 R⊙, R2=1.33±0.02 R⊙, L1=5.0±0.6 L⊙, and L2=0.96±0.09 L⊙. We applied multiple frequency analyses to the eclipse-subtracted light residuals and detected the 42 frequencies below 2.5 days-1. Among these, three independent frequencies of f2, f3, and f4 can be identified as high-order (38≤n≤40) low-degree (l=2) gravity-mode oscillations, whereas the other frequencies may be orbital harmonics and combination terms. The ratios between the orbital frequency and the pulsation frequencies are forb:f2-4≃2:3, which implies that the γ Dor pulsations of the detached primary star may be excited by the tidal interaction of the secondary companion. The short orbital period, and the low mass ratio and M2 demonstrate that KIC 6206751 is an R CMa-type star, which is most likely evolving into an EL CVn star. Of seven well-studied R CMa-type stars, our program target is the only eclipsing binary with a γ Dor pulsating component.