Starspot Activity without Pulsation in the Binary System KIC 5444392 Revisited

Abstract

We revisited the short-period (∼1.5 days) binary system KIC 5444392, which shows quasi-period modulated light variations. Previous studies indicated that these variations might be caused by stellar pulsations. In our work, we used the PHOEBE program, which revealed that this binary is an almost circular (e ≈0.007) detached system with two G-type stars. The masses and radii of the primary and secondary stars were obtained as M1=1.21±0.06M⊙, R1=1.69±0.09R⊙ and M2=1.27±0.06M⊙, R2=1.69±0.09R⊙, respectively. Based on these parameters, the isochrone fitting showed that this system consists of a subgiant and a main-sequence star, whose ages are 3.89−0.34+0.37 Gyr. Neither the primary nor the secondary star is in the mass range of Cepheid and Gamma Dor. Fourier analysis showed that the fitting residuals varied stochastically in a frequency around the orbital frequency, which means that the quasi-periodic signals resulted from starspots rather than stellar pulsation. Similar stellar parameters of both components of KIC 5444392 and the frequency analysis lead us to believe that starspots are in both stars. The autocorrelation analysis on the residuals indicates that the decay timescale of the starspots is about 53 days, and the rotational periods of both stars are very close to the orbital period of the binary. This result adheres to the trend that the decay timescale increases following the rotational frequency. Thus, studying this binary could increase our understanding of the light variations in the binary system.