Two Kepler red-giant eclipsing binaries as lower red-giant branch benchmarks for asteroseismic scaling relations. Dynamical masses and radii from JKTEBOP and PHOEBE-2 modeling

Abstract

Space-based photometry has detected solar-like oscillations in thousands of stars, whose global seismic parameters yield stellar properties via the asteroseismic scaling relations. Because these relations systematically overestimate red-giant masses and radii empirical calibration is required. Double-lined eclipsing binaries hosting oscillating red giants provide precise dynamical masses and radii without external calibration, making them ideal benchmarks. We present KIC 8129189 and KIC 10920813, two Kepler eclipsing binaries containing less-evolved oscillating red giants, as new benchmarks that extend the calibration sample toward smaller radii. We measured radial velocities from high-resolution spectra, extracted global asteroseismic parameters from Kepler light curves, and modeled the binaries with JKTEBOP and PHOEBE-2 using both full light curves and selected eclipse sets, adopting benchmark masses and radii from the envelope of tested model/data configurations. We then fit correction factors $f_{\Delta \nu }$ and $f_{{\nu }_{max}}$ to the underlying $\Delta \nu$-density and ${\nu }_{max}$-surface-gravity relations. We obtain $M_{RG}=1.413\pm 0.037M_{\odot }$ and $R_{RG}=4.296\pm 0.061R_{\odot }$ for KIC 8129189, and $M_{RG}=1.383\pm 0.022M_{\odot }$ and $R_{RG}=5.914\pm 0.043R_{\odot }$ for KIC 10920813. The adopted 15-star calibration gives $f_{\Delta \nu }=0.9777\pm 0.0048$ and $f_{{\nu }_{max}}=1.024\pm 0.008$, corresponding to $C_M=0.850\pm 0.020$ and $C_R=0.9333\pm 0.0090$. Neither correction factor depends significantly on radius, nor does $f_{{\nu }_{max}}$ depend on metallicity; model-based $f_{\Delta \nu }$ values are systematically lower than the dynamically derived ones. Both systems agree with the correction from previous benchmarks, showing that continued expansion of the eclipsing-binary sample is essential for testing the scaling relations across evolutionary stage.

24 pages, 20 figures