KIC 5768203: A δ Sct Pulsator Modulated by Rotation and Spots

Abstract

We perform a detailed analysis of the Kepler target KIC 5768203 based on the Kepler and Transiting Exoplanet Survey Satellite (TESS) data. Three independent frequencies are detected by Fourier analysis of the Kepler long-cadence data: two pulsation frequencies f P0 = 7.807874(2) day−1 and f P1 = 9.970035(6) day−1, which have amplitudes below 1.4 mmag in the Kepler band, and one modulation frequency f rot = 0.45813(1) day−1. Based on a period ratio of 0.7803, f P0 and f P1 are supposed to be radial frequencies. However, further confirmation is needed. Based on the triplets and phase variations of the two pulsation frequencies, the star is possibly a δ Sct pulsator in a binary system. The modulation frequency f rot and its four harmonics could be attributed to the stellar rotation and surface spots. With the rotation frequency f rot, the rotation velocity of the star is estimated to be 75(3) km s−1. By analyzing the phase diagram without pulsations, it is inferred that there are starspots (or clusters of starspots) of large area on the surface of KIC 5768203. These starspots are slowly evolving in position and brightness over the course of the Kepler long-cadence observations. The finding of the rotation frequency in the TESS data implies the long-term presence of starspots on the surface of KIC 5768203.