A binary-based reassessment of the age and stellar properties of NGC 7789 using 12 binary components

ABSTRACT We present a binary-based reassessment of the age of the intermediate-age open cluster NGC 7789, together with well-constrained stellar parameters for 12 components in 6 SB2 systems, including two eclipsing binaries. Our analysis employs a unified modelling framework that combines radial-velocity orbits, Transiting Exoplanet Survey Satellite (TESS) light curves, and blue-to-infrared (IR) spectral energy distributions (SEDs), providing a robust alternative to traditional isochrone-based age determinations. By adopting common cluster-wide parameters (age, distance, and line-of-sight extinction) when solving for the stellar parameters of the binary components, we obtain a coherent set of masses, radii, effective temperatures, and luminosities for all 12 stars. The combined SED, eclipsing-binary, and radial-velocity analysis yields a well-constrained cluster age of 1. 26 0. 09 Gyr and an extinction of AV = 0. 90 0. 05 mag, while remaining consistent with the Gaia DR3 distance of d 2. 06 kpc used as an external prior. An independent Gaia DR3 astrometric analysis gives a distance of 2082 142 pc and confirms the membership of all six systems. The 12 binary components occupy the turnoff and sub-giant regions of the cluster, enabling stringent evolutionary tests: in the radius–mass, radius–temperature, and temperature–mass diagrams, they show excellent agreement with modern stellar evolution models for the derived cluster parameters. NGC 7789 has long been affected by age discrepancies arising from main-sequence turnoff (MSTO) broadening, rotation, and differential reddening, with literature estimates spanning 1. 1 to 1. 6 Gyr. Our binary-anchored analysis significantly narrows this range and demonstrates that a self-consistent set of parameters emerges when dynamical SB2 information, eclipsing-binary geometry, and SED constraints are jointly analysed. NGC 7789 thus serves as a valuable benchmark for multi-observable, binary-based age determinations in open cluster studies.