KIC 5623923: A Faint Eclipsing Binary Consisting of $δ$ Scuti pulsations

Abstract: In this paper, we present a detailed analysis of the light variation of KIC 5623923 using high-precision time-series data from the $Kepler$ mission. The analysis reveals this target is an eclipsing binary system with $δ$ Scuti type pulsations from the primary component, rather than from the secondary as previously reported. The frequency analysis of three short-cadence data reveals 41 significant frequencies, including the orbital frequency ($f_{orb}$ = 0.827198 d$^{-1}$) due to orbital motion from binary system and the pulsational frequencies. Most of the pulsational signal lies in the frequency range of 20 - 32 d$^{-1}$, with amplitude between 0.3 and 8.8 mmag, in which seven peaks are identified as `independent' modes. The strongest one ($f_{3}$ = 28.499399 d$^{-1}$) likely corresponds to a high-order radial mode. In other peaks ($f_{7}$, $f_{10}$, and $f_{18}$), several pairs of multiplet structures centered on them are found. The fitting of spectral energy distribution (SED) using the collected photometry measurement of multiple bands reveals the effective temperatures of the primary and secondary components as $8348^{+230}_{-225}$~K and $4753^{+237}_{-229}$~K, respectively, which place the primary star in the classical pulsating instability zone. The characteristic light curve morphology and short orbital period are consistent with a tidally locked system. Based on the characteristics of amplitude spectra of pulsating stars in close binaries, the analysis of the multiplet structures reveals that three independent frequencies (i.e. $f_{7}$, $f_{10}$, and $f_{18}$) correspond to non-radial modes with $l = 2$, while the associated sidelobes are produced by the orbital motion. We highlight the potential of this method in future studies of pulsating binary stars.