2017MNRAS.467.4663S

We searched for extrasolar planets around pulsating stars by examining Kepler data for transit-like events hidden in the intrinsic variability. All short-cadence observations for targets with 6000 < T_eff < 8500 K were visually inspected for transit-like events following the removal of pulsational signals by sinusoidal fits. Clear transit-like events were detected in KIC 5613330 and KIC 8197761. KIC 5613330 is a confirmed exoplanet host (Kepler-635b), where the transit period determined here is consistent with the literature value. KIC 8197761 is a γ Doradus-δ Scuti star exhibiting eclipses/transits occurring every 9.868 6667(27) d, having durations of 8.37 h and causing brightness drops Δ/FF = 0.006 29(29). The star's pulsation spectrum contains several mode doublets and triplets, identified as l = 1, with a mean spacing of 0.001 659(15) d^–1 , implying an internal rotation period of 301 ± 3 d. Trials to calculate the size of the light travel time effect (LTTE) from the pulsations to constrain the companion's mass ended inconclusive. Finding planets around γ Doradus stars from the pulsational LTTE, therefore, is concluded to be unrealistic. Spectroscopic monitoring of KIC 8197761 revealed sinusoidal radial velocity variations with a semi-amplitude of 19.75 ± 0.32 km s^–1, while individual spectra present rotational broadening consistent with vsin i = 9 ± 1 km s^–1. This suggests that the stellar surface rotation is synchronized with the orbit, whereas the stellar core rotates ∼30 times slower. Combining the observed radial velocity variability with the transit photometry, constrains the companion's mass to be ≃0.28 M_☉, ruling out an exoplanet hypothesis.