Pulsations of the Rapidly Oscillating Ap Star KIC 10685175 Revisited by TESS

Abstract

KIC 10685175 (TIC 264509538) was discovered to be a rapidly oscillating Ap star from Kepler long-cadence data using super-Nyquist frequency analysis. It was reobserved by the Transiting Exoplanet Survey Satellite (TESS) with 2 minute cadence data in Sectors 14 and 15. We analyzed the TESS light curves, finding that the previously determined frequency is a Nyquist alias. The revised pulsation frequency is 191.5151 ± 0.0005 day−1 (P = 7.52 minutes) and the rotation frequency is 0.32229 ± 0.00005 day−1 (Prot = 3.1028 days). The star is an oblique pulsator with a pulsation amplitude modulated by the rotation, reaching a maximum pulsation amplitude at the time of the rotational light minimum. The oblique pulsation generates a frequency quintuplet split by exactly the rotation frequency. The phases of sidelobes, the pulsation phase modulation, and a spherical harmonic decomposition all show this star to be pulsating in a distorted quadrupole mode. Following the oblique pulsator model, we calculated the rotation inclination i and magnetic oblique β of this star, which provide detailed information of pulsation geometry. The i and β derived by the best fit of pulsation amplitude and phase modulation through a theoretical model differ from those calculated for a pure quadrupole, indicating the existence of strong magnetic distortion. The model also predicts the polar magnetic field strength is as high as about 6 kG which is predicted to be observed in a high-resolution spectrum of this star.