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

TL;DR

This paper addresses the origin of δ Scuti-type pulsations in the faint eclipsing binary KIC 5623923 using high-precision Kepler short-cadence data. It combines Fourier analysis, spectral-energy-distribution fitting, and neural-network informed PHOEBE modeling to disentangle pulsations from binary effects, concluding that the pulsations arise from the hotter primary star and that the system is tidally synchronized. The study identifies 41 significant frequencies, with seven independent p-modes mainly in the $20-35$ d$^{-1}$ range, and detects multiplet structures around several modes that indicate orbital modulation consistent with $l=2$ non-radial pulsations. These results place the primary in the δ Scuti instability strip and demonstrate a powerful framework for probing pulsations in faint binary systems, with implications for future asteroseismic investigations and space-based survey planning.

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.

Figures (9)

• Figure 1: The light curve of KIC 5623923 in full SC Quarter 14.1, clearly showing the typical light variations of an eclipsing binary system with superposition of pulsations.
• Figure 2: Top panel: the amplitude spectrum of SC data for KIC 5623923 up to 35 d$^{-1}$, the blue dashed lines refer to the positions of the orbital frequency $f_{orb}$ and its harmonics up to 10$f_{orb}$. Middle panel: the amplitude spectrum after prewhitening of 20 strongest peaks, the blue dashed lines refer to harmonics of the orbital frequency up to 18$f_{orb}$. Bottom panel: the residual spectrum after extraction of all significant frequencies, to an amplitude limit of about 0.1 mmag. The red dot-dashed curve refers to the detection limit of S/N = 4.0. No peak is statistically significant in the residual.
• Figure 3: Phase-folded light curve of KIC 5623923 on the orbital frequency ($f_{1}$), with pulsations removed. The red circles represent the data binned into 100 phase intervals.
• Figure 4: Amplitude spectrum of SC data for KIC 5623923 in frequency region of 20 - 32 d$^{-1}$, clearly showing the multiplet structures around $f_{7}$, $f_{10}$, and $f_{18}$. Asterisk ($\ast$) refers to positions of the independent frequencies and circle ($\circ$) refers to the combinations with $f_{orb}$.
• Figure 5: The SED fitting result. Upper panel: Cyan points are the observed fluxes, and red diamonds are the synthetic fluxes. The black spectrum is the best-fit SED model, while the green and blue curves are the model spectra of primary and secondary stars, respectively. Lower panel: the residuals of SED fitting. The photometric observations in different bands are sorted in the order of Table \ref{['tab:obs_mags']}.