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We report the discovery of a post-mass transfer Gamma Doradus/Delta Scutihybrid pulsator in the eclipsing binary KIC~9592855. This binary has a circularorbit, an orbital period of 1.2 days, and contains two stars of almostidentical masses ($M_1=1.72M_{\odot}, M_2=1.71M_{\odot}$). However, the coolersecondary star is more evolved ($R_2=1.96R_{\odot}$) while the hotter primaryis still on the zero-age-main-sequence ($R_1=1.53R_{\odot}$). Coeval modelsfrom single star evolution cannot explain the observed masses and radii, andbinary evolution with mass-transfer needs to be invoked. After subtracting thebinary light curve, the Fourier spectrum shows low-order pressure-modepulsations, and more dominantly, a cluster of low-frequency gravity modes atabout $2$ day$^{-1}$. These g-modes are nearly equally-spaced in period, andthe period spacing pattern has a negative slope. We identify these g-modes asprograde dipole modes and find that they stem from the secondary star. Thefrequency range of unstable p-modes also agrees with that of the secondary. Wederive the internal rotation rate of the convective core and the asymptoticperiod spacing from the observed g-modes. The resulting values suggest that thecore and envelope rotate nearly uniformly, i.e., their rotation rates are bothsimilar to the orbital frequency of this synchronized binary.

Gravity Modes Reveal the Internal Rotation of a Post-mass Transfer Gamma Doradus/Delta Scuti Hybrid Pulsator in Kepler Eclipsing Binary KIC 9592855