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Abstract Gyrochronology is the empirical relation between rotation and age. NASA's Transiting Exoplanet Survey Satellite (TESS), Kepler, and K2 missions have observed thousands of wide main sequence binaries. Since components of a binary are coeval, their rotation periods should be consistent with gyrochronology models. However, the usefulness of gyrochronology depends upon reliable rotation periods. We explore the reliability of rotation period determinations for a sample of wide binary components from the TESS cycle 3. Wide binaries with the most reliable rotation period determinations provide a strong basis for testing whether the gyrochronology empirical relation derived from open clusters is also valid for field stars. 

Abstract Accurate stellar ages are essential for our understanding of the star formation history of the Milky Way and Galactic chemical evolution, as well as to constrain exoplanet formation models. Gyrochronology, a relationship between stellar rotation and age, appears to offer a reliable age indicator for main-sequence (MS) stars over the mass range of approximately 0.6–1.3M_⊙. Those stars lose their angular momentum due to magnetic braking and as a result their rotation speeds decrease with age. Although current gyrochronology relations have been fairly well tested for young MS stars with masses greater than 1M_⊙, primarily in young open clusters, insufficient tests exist for older and lower mass MS stars. Binary stars offer the potential to expand and fill in the range of ages and metallicity over which gyrochronology can be empirically tested. In this paper, we demonstrate a Monte Carlo approach to evaluate gyrochronology models using binary stars. As examples, we used five previously published wide binary pairs. We also demonstrate a Monte Carlo approach to assess the precision and accuracy of ages derived from each gyrochronology model. For the traditional Skumanich models, the age uncertainties areσ_age/age = 15%–20% for stars withB−V= 0.65 andσ_age/age = 5%–10% for stars withB−V= 1.5 and rotation periodP≤ 20 days. 

Abstract We construct a sample of nearly 30,000 main-sequence stars with 4500 K < T_eff < 5000 K and stellar ages estimated by the chromospheric activity−age relation. This sample is used to determine the age distribution in theR–Zplane of the Galaxy, whereRis the projected Galactocentric distance in the disk midplane andZis the height above the disk midplane. As ∣Z∣ increases, the percentage of old stars becomes larger. It is known that scale-height of Galactic disk increases asRincreases, which is called a flare. A mild flare fromR ∼ 8.0 to 9.0 kpc in stellar age distribution is found. We also find that the velocity dispersion increases with age as confirmed by previous studies. Finally we present spiral-shaped structures inZ–υ_Zphase space in three stellar age bins. The spiral is clearly seen in the age bin of [0, 1] Gyr, which suggests that a vertical perturbation to the disk probably took place within the last ∼1.0 Gyr. 

Abstract We identify member stars of more than 90 open clusters in the LAMOST survey. With the method of Fang et al., the chromospheric activity (CA) indices,for 1091 member stars in 82 open clusters andfor 1118 member stars in 83 open clusters, are calculated. The relations between the average,in each open cluster and its age are investigated in differentT_effand [Fe/H] ranges. We find that CA starts to decrease slowly from logt = 6.70 to logt = 8.50, and then decreases rapidly until logt = 9.53. The trend becomes clearer for cooler stars. The quadratic functions between logR′ and logtwith 4000 K  < T_eff < 5500 K are constructed, which can be used to roughly estimate ages of field stars with accuracy about 40% forand 60% for.