Abstract

As stars age, they lose mass and angular momentum resulting in a surface rotation spin-down over time. Gyrochronology is a promising tool for age dating where other methods fail but requires calibration using stars with well-known age and rotation periods to be successful. Due to the limited amount of calibrators with precise ages, gyrochronology struggles to accurately predict the rotation periods of low-mass-cool stars. In this work, we utilize the coevality of HIP 43232--a wide-binary system comprised of a solar-like star with an M dwarf companion--to add a new calibrator in the cool-low-mass regime of gyrochronology. Using a combination of spectroscopic and asteroseismic constraints, we precisely characterize the solar-like component HIP 43232A through MESA modeling. We also explore the effects on several stellar parameters by choosing different potential input physics combinations when modeling with MESA. MESA estimates the age of HIP 43232A to be ~3.7 Gyr, a regime that hosts an extremely limited population of M dwarfs with precisely measured ages. Pairing K2 with ZTF light curves, we estimate the rotation period of HIP 43232B, the M dwarf companion, to be 41.3 +— 4.1 days. Period-age relationships from the literature overpredict the amount of angular momentum loss and predict a slower period for HIP 43232B than we observe. However, models that account for internal angular momentum transport include a period of spin-down stall and predict the rotation period of HIP 43232B significantly better. HIP 43232B is one of the first M dwarfs with a precisely measured age and rotation period in this regime, making it a benchmark calibrator for future gyrochronology models.