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arXiv · 2305.05024

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

Arthur Alencastro Puls·Luca Casagrande·Stephanie Monty·David Yong·Fan Liu·Dennis Stello·Mikkel N. Lund
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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 ($\geq$11 Gyr), super metal rich ($\geq$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.

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Arthur Alencastro Puls, Luca Casagrande, Stephanie Monty, David Yong, Fan Liu, Dennis Stello, Mikkel N. Lund. 2023-05-08. The odd bunch: chrono-chemo-dynamics of sixteen unusual stars from Kepler. https://doi.org/10.1093/mnras/stad1365

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