Filling the Gap: Calibrating Gyrochronology at 1.3 Gyr with the Benchmark Cluster NGC-752

Empirical gyrochronology uses co-eval clusters to calibrate stellar rotation versus mass and age, but existing benchmarks at ~1 Gyr (NGC-6811) and ~2.5 Gyr (NGC-6819) left the intermediate-age spin-down behavior poorly constrained. Combining Gaia-based membership lists with literature rotation periods, the authors map NGC-752's slow-rotator sequence at an assumed age of 1.3 Gyr for the first time.

They identify a well-defined sequence intermediate between the younger and older clusters: stars near Teff ~ 4500 K rotate more slowly than NGC-6811 counterparts, showing that stalled spin-down at ~1 Gyr resumes by NGC-752's age. Existing empirical gyrochronology models overestimate ages of many G and early-K dwarfs by 20–50% without this intermediate-age anchor, though part of the offset may stem from NGC-752's absolute age uncertainty. This calibration is timely because Gaia DR4, Roman, and PLATO are expected to deliver rotation periods for tens of millions of stars.