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Determining the precise ages of young (tens to a few hundred Myr) kinematic ('moving') groups is important for placing star, protoplanetary disc, and planet observations on an evolutionary timeline. The nearby ∼25 Myr-old β Pictoris Moving Group (BPMG) is an important benchmark for studying stars and planetary systems at the end of the primordial disc phase. Gaia DR3 astrometry and photometry, combined with ground-based observations and more sophisticated stellar models, permit a systematic re-evaluation of BPMG membership and age. We combined Gaia astrometry with previously published radial velocities to evaluate moving group membership in a Bayesian framework. To minimize the effect of unresolved stellar multiplicity on age estimates, we identified and excluded multistar systems using Gaia astrometry, ground-based adaptive optics imaging, and multi-epoch radial velocities, as well as literature identifications. We estimated age using isochrone and lithium-depletion-boundary fitting with models that account for the effect of magnetic activity and spots on young, rapidly rotating stars. We find that age estimates are highly model-dependent; Dartmouth magnetic models with ages of 23 ± 8 and 33 |$^{+9}_{-11}$| Myr provide best fits to the lithium depletion boundary and Gaia M G versus B P –R P colour–magnitude diagram, respectively, whereas a Dartmouth standard model with an age of 11 |$^{+4}_{-3}$| Myr provides a best fit to the 2-Micron All-Sky Survey- Gaia |$M_{K_S}$| versus B P– R P colour–magnitude diagram. [ABSTRACT FROM AUTHOR]

Current spectroscopic surveys are producing large catalogs of chemical abundances for stars of all types. The yttrium-to-magnesium ratio, [Y/Mg], has emerged as a candidate age indicator for solar twins in the local stellar neighborhood. However, it is unclear whether it is a viable age diagnostic for more diverse stellar types, so we investigate [Y/Mg] as an age indicator for the FGK-type planet host stars observed by Kepler. We find that the [Y/Mg] “Clock” is most precise for solar twins, with a [Y/Mg]/age slope of m = âˆ'0.0370 ±0.0071 dex Gyrâˆ'1 and σ Age = 2.6 Gyr. We attribute the lower precision compared to literature results to nonsolar twins contaminating our solar twin sample and recommend a 1.5 Gyr systematic uncertainty for stellar ages derived with any [Y/Mg]â€"Age relation. We also analyzed the [Y/Mg] Clock as a function of T eff, log g , and metallicity individually and find no strong trends, but we compute statistically significant [Y/Mg]â€"Age relations for subsamples defined by ranges in T eff, log g , and metallicity. Finally, we compare [Y/Mg] and rotation ages and find statistically similar trends as for isochrone ages, although we find that rotation ages perform better for GK dwarfs while isochrones perform better for FG subgiants. We conclude that the [Y/Mg] Clock is most precise for solar twins and analogs but is also a useful age diagnostic for FGK stars. [ABSTRACT FROM AUTHOR]

Stellar rotation is a complex function of mass, metallicity, and age and can be altered by binarity. To understand the importance of these parameters in main-sequence stars, we have assembled a sample of observations that spans a range of these parameters using a combination of observations from The Transiting Exoplanet Survey Satellite (TESS) and the Kepler Space Telescope. We find that while we can measure rotation periods and identify other classes of stellar variability (e.g., pulsations) from TESS light curves, instrument systematics prevent the detection of rotation signals longer than the TESS orbital period of 13.7 days. Due to this detection limit, we also use rotation periods constrained using rotational velocities measured by the APOGEE spectroscopic survey and radii estimated using the Gaia mission for both TESS and Kepler stars. From these rotation periods, we (1) find we can track rotational evolution along discrete mass tracks as a function of stellar age, (2) find we are unable to recover trends between rotation and metallicity that were observed by previous studies, and (3) note that our sample reveals that wide binary companions do not affect rotation, while close binary companions cause stars to exhibit more rapid rotation than single stars. [ABSTRACT FROM AUTHOR]

Given their location on the Hertzsprung-Russell (H-R) diagram, thoroughly characterized subgiant stars can place stringent constraints on a wide range of astrophysical problems. Accordingly, they are prime asteroseismic targets for the Transiting Exoplanet Survey Satellite (TESS) mission. In this work, we infer stellar properties for a sample of 347 subgiants located in the TESS Continuous Viewing Zones, which we select based on their likelihood of showing asteroseismic oscillations. We investigate how well they can be characterized using classical constraints (photometry, astrometry) and validate our results using spectroscopic values. We derive luminosities, effective temperatures, and radii with mean 1σ random (systematic) uncertainties of 4.5% (2%), 33 K (60 K), and 2.2% (2%), as well as more model-dependent quantities such as surface gravities, masses, and ages. We use our sample to demonstrate that subgiants are ideal targets for mass and age determination based on H-R diagram location alone, discuss the advantages of stellar parameters derived from a detailed characterization over widely available catalogs, show that the generally used 3D extinction maps tend to overestimate the extinction for nearby stars (distance ≲500 pc), and find a correlation that supports the rotation–activity connection in post-main-sequence stars. The complementary roles played by classical and asteroseismic data sets will open a window to unprecedented astrophysical studies using subgiant stars. [ABSTRACT FROM AUTHOR]

Most previous efforts to calibrate how rotation and magnetic activity depend on stellar age and mass have relied on observations of clusters, where isochrones from stellar evolution models are used to determine the properties of the ensemble. Asteroseismology employs similar models to measure the properties of an individual star by matching its normal modes of oscillation, yielding the stellar age and mass with high precision. We use 27 days of photometry from the Transiting Exoplanet Survey Satellite to characterize solar-like oscillations in the G8 subgiant of the 94 Aqr triple system. The resulting stellar properties, when combined with a reanalysis of 35 yr of activity measurements from the Mount Wilson HK project, allow us to probe the evolution of rotation and magnetic activity in the system. The asteroseismic age of the subgiant agrees with a stellar isochrone fit, but the rotation period is much shorter than expected from standard models of angular momentum evolution. We conclude that weakened magnetic braking may be needed to reproduce the stellar properties, and that evolved subgiants in the hydrogen shell-burning phase can reinvigorate large-scale dynamo action and briefly sustain magnetic activity cycles before ascending the red giant branch. [ABSTRACT FROM AUTHOR]