The odd bunch: chrono-chemo-dynamics of sixteen unusual stars from Kepler

Abstract

In this study we combine asteroseismic, spectroscopic and kinematic information to perform a detailed analysis of a sample of 16 stars from the Kepler field. Our selection focuses on stars that appear to contradict Galactic chemical evolution models: young and $\alpha$-rich, old and metal-rich, as well as other targets with unclear classification in past surveys. Kinematics are derived from Gaia DR3 parallaxes and proper motions, and high-resolution spectra from HIRES/Keck are used to calculate chemical abundances for over 20 elements. This information is used to perform careful checks on asteroseismic masses and ages derived via grid-based modelling. Among the seven stars previously classified as young and $\alpha$-rich, only one seems to be an unambiguously older object masking its true age. We confirm the existence of two very old ($\ge$11 Gyr), super metal rich ($\ge$0.1 dex) giants. These two stars have regular thin disc chemistry and in-plane solar circle orbits which fit well in the picture of radial migration via the churning mechanism. The alternative explanation that these stars have younger ages would require mass-loss rates which strongly increases with increasing metallicity. Finally, we suggest further investigations to explore the suitability of Zn as a chemical clock in red giants.

10 pages, 7 figures, accepted for publication in MNRAS

References in corpus (39)

• Array Programming with NumPy
• Estimating distances from parallaxes. V: Geometric and photogeometric distances to 1.47 billion stars in Gaia Early Data Release 3
• galpy: A Python Library for Galactic Dynamics
• The mass distribution and gravitational potential of the Milky Way
• Gaia Early Data Release 3: Parallax bias versus magnitude, colour, and position
• New constraints on the chemical evolution of the solar neighbourhood and Galactic disc(s). Improved astrophysical parameters for the Geneva-Copenhagen Survey
• The GALAH+ Survey: Third Data Release
• Basic physical parameters of a selected sample of evolved stars
• Riding the Spiral Waves: Implications of Stellar Migration for the Properties of Galactic Disks
• APOGEE Data and Spectral Analysis from SDSS Data Release 16: Seven Years of Observations Including First Results from APOGEE-South
• The APOKASC Catalog: An Asteroseismic and Spectroscopic Joint Survey of Targets in the Kepler Fields
• Standing on the shoulders of Dwarfs: the Kepler asteroseismic LEGACY sample II - radii, masses, and ages
• Standing on the shoulders of Dwarfs: the $Kepler$ asteroseismic LEGACY sample I - oscillation mode parameters
• Radial mixing and the transition between the thick and thin Galactic discs
• Mixed modes in red giants: a window on stellar evolution
• A First Constraint on the Thick Disk Scale Length: Differential Radial Abundances in K Giants at Galactocentric Radii 4, 8, and 12 kpc
• A non-LTE study of neutral and singly-ionized calcium in late-type stars
• Young [$\alpha$/Fe]-enhanced stars discovered by CoRoT and APOGEE: What is their origin?
• Age dissection of the Milky Way discs: red giants in the Kepler field
• The Ages of the Thin Disk, Thick Disk, and the Halo from Nearby White Dwarfs
• Non-LTE aluminium abundances in late-type stars
• The First APOKASC Catalog of Kepler Dwarf and Subgiant Stars
• Determining stellar parameters of asteroseismic targets: going beyond the use of scaling relations
• Stroemgren survey for Asteroseismology and Galactic Archaeology: let the SAGA begin
• NGC 6819: testing the asteroseismic mass scale, mass loss, and evidence for products of non-standard evolution
• Mg line formation in late-type stellar atmospheres: I. The model atom
• The GALAH survey: effective temperature calibration from the InfraRed Flux Method in the Gaia system
• Solar oxygen abundance
• Mass loss along the red giant branch in 46 Globular Clusters and their multiple populations
• The BAyesian STellar Algorithm (BASTA): a fitting tool for stellar studies, asteroseismology, exoplanets, and Galactic archaeology
• Discovery of post-mass-transfer helium-burning red giants using asteroseismology
• The K2 Galactic Archaeology Program Data Release 3: Age-abundance patterns in C1-C8 and C10-C18
• Origin of $\alpha$-rich young stars: clues from C, N and O
• PBjam: A Python package for automating asteroseismology of solar-like oscillators
• Most "young" $\alpha$-rich stars have high masses but are actually old
• Asteroseismic properties of solar-type stars observed with the NASA K2 mission: results from Campaigns 1-3 and prospects for future observations
• Cannibals in the thick disk II -- Radial-velocity monitoring of the young alpha-rich stars
• The GALAH Survey: Temporal Chemical Enrichment of the Galactic Disk
• Chemo-dynamics and asteroseismic ages of seven metal-poor red giants from the Kepler field