Asteroseismology and Dynamics Reveal Interior Structure and Coeval Evolution in the Triply Post-Main-Sequence system DG Leo

TL;DR

DG Leo is a hierarchical triple system where a well-separated delta Scuti pulsator enables precise dynamical constraints on all three components when combined with TESS photometry and archival spectroscopy. The study employs Wilson–Devinney modeling of four TESS sectors to derive a detached inner binary with near-equal masses (~2.26 M⊙) and radii (~3.3 R⊙), plus a distant companion B of mass ~2.39 M⊙. Seven independent delta Scuti frequencies are fitted via asteroseismic modeling on grids constrained by the dynamical solution, allowing simultaneous tracing of the pulsator's evolution and the system's stage. The results indicate all components are in the post-main-sequence phase, with an age of $0.7664^{+0.1402}_{-0.1258}$ Gyr and a convective core extent of $R_{cz}/R = 0.0562^{+0.0137}_{-0.0021}$, demonstrating coeval evolution and providing precise interior-structure constraints for a complex multiple-star system.

Abstract

$δ$ Scuti stars in binary or multiple systems serve as crucial probes for studying stellar pulsation and evolution. However, many such systems are not ideal for asteroseismology due to uncertainties in mass transfer with close companions and the challenges of dynamically measuring all components' physical properties. The triple system DG~Leo, comprising an inner binary and a distant $δ$ Scuti star, is an ideal target due to its well-separated pulsator. By combining new \textit{TESS} photometry with archival spectroscopy, our dynamical analysis shows that the system's three components share similar masses, radii, and luminosities within errors, occupying coincident Hertzsprung--Russell diagram positions, indicative of coeval evolution. By fitting seven observed $δ$ Scuti frequencies through asteroseismic modeling with dynamically constrained theoretical grids, we simultaneously trace the pulsating star's evolution and constrain the triple system's evolutionary stage, with the derived fundamental parameters showing consistency with the dynamical solutions. Our analysis reveals that all three components of DG~Leo are in the post-main-sequence phase, with a system age of $0.7664^{+0.1402}_{-0.1258}$~Gyr. Additionally, the $δ$ Scuti component shows multiple non-radial modes with significant mixed-character frequencies, providing precise constraints on its convective core extent ($R_{\mathrm{cz}}/R = 0.0562^{+0.0137}_{-0.0021}$).

Figures (3)

• Figure 1: The TESS light curve and corresponding Fourier amplitude spectrum of DG Leo. Top panel: the full light curve from Sector 21. Second panel: the Fourier amplitude spectrum derived from the full light curve. The dominant frequency peak at 0.4822 d$^{-1}$ (red dashed vertical line) corresponds to ellipsoidal variations, while other significant peaks represent pulsation frequencies. Third panel: the light curve after removing the dominant ellipsoidal variations. Bottom panel: a zoomed-in view of the detrended light curve between TJD 1872--1876.5. (TJD = BJD $-$ 2457000.0).
• Figure 2: The light curves from four TESS sectors and their corresponding phase-binned light curves (green circles) are overplotted with the best-fitting model (red solid curves; W-D Model 2). Residuals are shown in the bottom panel for each sector.
• Figure 3: The light curve of DG Leo after subtracting the binary model, along with its corresponding Fourier spectra. Top panel: the residual light curve (blue dots) with the Fourier fit model overplotted (red curve). The inset shows a zoomed-in view of the same light curve between TJD 1872 and 1874. Middle panel: the Fourier amplitude spectrum of the residual light curve; the seven independent frequencies are marked by colored vertical dashed lines. Bottom panel: the residual spectrum after pre-whitening with 40 significant frequencies.