Exploring Gyrochronology with Young Clusters, Field Binaries, and Post-MS Stars in the Gaia Era.

Rotation plays an important role in the life of stars and offers a potential diagnostic to infer their ages and that of their planets. This idea is known as gyrochronology, and while potentially fruitful over a wide range of ages and masses, recent results have raised concerns regarding its applicability. I have carried out three efforts to examine gyrochronology in different evolutionary regimes. Regarding young stars (< 1 Gyr), my work illustrates the impact that removing the non-member contamination by using the precise Gaia astrometry has on the rotational sequences of open clusters. The clean and updated sequences demonstrate that ground-based rotation periods can be as constraining as space-based periods, strengthen the evidence of core-envelope decoupling in K-dwarfs, confirm that M-dwarfs are born rapidly rotating with strong mass-dependent trends, and show that solar-type stars quickly converge onto a uniform rotational sequence (~ 0.5 Gyr). Regarding old stars (~ few Gyr), I have found that the component of co-eval wide binaries have rotation rates that often do not follow the expectations from standard gyrochronology, which adds to the evidence that spin-down behavior becomes complicated in old systems. Finally, in the context of post-MS stars, the results from a detailed subgiant characterization study show supporting evidence for the rotation-activity connection in post-MS stars, and demonstrate that subgiants are ideal targets for precise age and mass determination based on HR diagram location alone. These stars are prime asteroseismic targets for the TESS mission and will place stringent constraints on angular momentum evolution theories.