KIC 9851142: A binary star with total eclipses and γ Dor pulsations

Abstract KIC 9851142 (V2094 Cyg, HD 188854) is an eccentric eclipsing binary with an orbital period of P orb = 8.4854  d, exhibiting millimagnitude (mmag) amplitude pulsations on time scales of a few days. I present the results of the analysis of high-resolution spectroscopic data and Kepler long and short cadence photometry. The iterative combination of spectral classification by atmospheric analysis, radial velocity and eclipse timing variation studies, separation of pulsational features of the light curve, and binary light curve analysis led to the accurate determination of the fundamental stellar parameters and the comparison with evolutionary models strict constraints on the system age. I found that the binary is composed of two main sequence stars with an age of 0.75 ± 0.21  Gyr, having masses, radii and temperatures of M 1 = 1.79 ± 0.11 M ⊙ , R 1 = 2.47 ± 0.07 R ⊙ , T eff1 = 7250 ± 480  K for the primary, and M 2 = 0.83 ± 0.12 M ⊙ , R 2 = 0.67 ± 0.05 R ⊙ , T eff2 = 5050 ± 650  K for the secondary. Multiple frequency analyses techniques were applied to the light residuals after subtracting the synthetic eclipsing curve from the Kepler data. This revealed that the primary component of KIC 9851142 is a γ Dor type pulsating star, exhibiting five pulsation frequencies in the range of 0.6–1.95 d −1 with amplitudes of 0.29–6.72 mmag and pulsation constants of 0.24–0.27 d. The analysis of the eclipse timing variations revealed preliminary apsidal motion with a period of P apse obs = 240 ± 29  y. Only six eclipsing binaries have been known to contain γ Dor pulsating components and, therefore, KIC 9851142 will be an important test-bed for examining these exceptional and interesting objects.