KIC 7756853: two hybrid δ Sct  γ Dor stars with Rossby and gravitoinertial pulsation modes in a doublelined spectroscopic system
Abstract
KIC 7756853 a bright Kepler target with a magnitude of (Kp = 8.96 mag), is a confirmed doublelined spectroscopic system following a comprehensive decadelong study of highresolution spectra. This system has an orbital period of 99.32 days, a mass ratio of 0.91, and consists of two Atype stars. Their individual properties include Teff of 9700 and 7600 K, log g of 4.7 and 4.0 cgs and vsini = 31 and 51 km/s, for the primary and the secondary components, respectively. In search of pulsation frequencies of KIC 7756853, Fourier analysis was applied to the complete Kepler longcadence data (Q0Q17), Kepler shortcadence data (Q1), and the Transiting Exoplanet Survey Satellite TESS light curves (sectors 1415, 4041, 5455). A total of 179 significant frequencies were detected, 31 of which are δ Scttype modes with frequencies ranging from 18.24 to 28.28 1/d. The most prominent mode, f_1, exhibited a frequency of 21.1416 1/d. Two distinct regular frequency splittings were observed in both pmodes and lowfrequency modes, linking these pulsation modes to two of the most significant low frequencies, i.e., f_3 =0.8914 1/d and f_9 = 2.5258 1/d. Significant lowfrequency modes, indicative of rmodes and gravitoinertial modes, were observed in the inertial range (0.7  5.1 1/d) and the superinertial range (5.1  7.8 1/d). The observed frequency splitting arises from the rotational effects of both primary and secondary components. It allows us to deduce a differential coretosurface rotation rate of 1.062 for the secondary and 1.003 for the primary components. The coupling of rotation and pulsation in KIC 7756853 suggests the presence of a pair of (γ Dor  δ Sct) hybrid pulsators with intermediate to fast rotations. Based on the coupling of rotation and orbital motion, a detected variability slightly longer than Kepler's Earthtrailing orbital period (∼1.30 1/yr) hints at possible stellar spots on both components or a third body in the system with a rotation frequency of 0.71 1/d.
 Publication:

EAS2024
 Pub Date:
 July 2024
 Bibcode:
 2024eas..conf...99S