Journal
ASTRONOMY & ASTROPHYSICS
Volume 645, Issue -, Pages -Publisher
EDP SCIENCES S A
DOI: 10.1051/0004-6361/202038307
Keywords
Galaxy: evolution; Galaxy: stellar content; Galaxy: structure; stars: late-type; stars: mass-loss; asteroseismology
Categories
Funding
- ERC Consolidator Grant [772293]
- European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme [804752]
- Center for Cosmology and AstroParticle Physics at The Ohio State University
- UK Science and Technology Facilities Council (STFC)
- International Space Science Institute (ISSI)
- FCT/MCTES
- FEDER through COMPETE2020 [UID/FIS/04434/2019, PTDC/FIS-AST/30389/2017, POCI-01-0145-FEDER-030389]
- ARC [FT160100402]
- ARC Centre of Excellence ASTRO 3D [CE170100013]
- Australian Research Council [FT190100574]
- DFG [CH1188/2-1]
- ChETEC COST Action - COST (European Cooperation in Science and Technology) [CA16117]
- NASA Science Mission directorate
- Alfred P. Sloan Foundation
- US Department of Energy Office of Science
- Center for High-Performance Computing at the University of Utah
- Brazilian Participation Group
- Carnegie Institution for Science
- Carnegie Mellon University
- Chilean Participation Group
- French Participation Group
- Harvard-Smithsonian Center for Astrophysics
- Instituto de Astrofisica de Canarias
- The Johns Hopkins University
- Kavli Institute for the Physics and Mathematics of the Universe (IPMU)/University of Tokyo
- Korean Participation Group
- Lawrence Berkeley National Laboratory
- Leibniz Institut fur Astrophysik Potsdam (AIP)
- Max-Planck-Institut fur Astronomie (MPIA Heidelberg)
- Max-Planck-Institut fur Astrophysik (MPA Garching)
- MaxPlanck-Institut fur Extraterrestrische Physik (MPE)
- National Astronomical Observatories of China
- New Mexico State University
- New York University
- University of Notre Dame
- Observatorio Nacional/MCTI
- The Ohio State University
- Pennsylvania State University
- Shanghai Astronomical Observatory
- United Kingdom Participation Group
- Universidad Nacional Autonoma de Mexico
- University of Arizona
- University of Colorado Boulder
- University of Oxford
- University of Portsmouth
- University of Utah
- University of Virginia
- University of Washington
- University of Wisconsin
- Vanderbilt University
- Yale University
- Australian Research Council [FT190100574] Funding Source: Australian Research Council
- STFC [ST/S000216/1] Funding Source: UKRI
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Ensemble studies of red-giant stars with precise seismic, spectroscopic, and astrometric constraints provide a new opportunity to address long-standing questions about stellar evolution and galaxy formation. The research reveals robust patterns in mass, age, chemical abundance, and orbital parameters, despite potential systematic uncertainties. The findings suggest efficient radial migration in the thin disc and confirm different chemo-dynamical histories of the chemical-thick and thin discs.
Ensemble studies of red-giant stars with exquisite asteroseismic (Kepler), spectroscopic (APOGEE), and astrometric (Gaia) constraints offer a novel opportunity to recast and address long-standing questions concerning the evolution of stars and of the Galaxy. Here, we infer masses and ages for nearly 5400 giants with available Kepler light curves and APOGEE spectra using the code PARAM, and discuss some of the systematics that may affect the accuracy of the inferred stellar properties. We then present patterns in mass, evolutionary state, age, chemical abundance, and orbital parameters that we deem robust against the systematic uncertainties explored. First, we look at age-chemical-abundances ([Fe/H] and [alpha /Fe]) relations. We find a dearth of young, metal-rich ([Fe/H] > 0.2) stars, and the existence of a significant population of old (8-9 Gyr), low-[alpha /Fe], super-solar metallicity stars, reminiscent of the age and metallicity of the well-studied open cluster NGC 6791. The age-chemo-kinematic properties of these stars indicate that efficient radial migration happens in the thin disc. We find that ages and masses of the nearly 400 alpha -element-rich red-giant-branch (RGB) stars in our sample are compatible with those of an old (similar to 11 Gyr), nearly coeval, chemical-thick disc population. Using a statistical model, we show that the width of the observed age distribution is dominated by the random uncertainties on age, and that the spread of the inferred intrinsic age distribution is such that 95% of the population was born within similar to 1.5 Gyr. Moreover, we find a difference in the vertical velocity dispersion between low- and high-[alpha /Fe] populations. This discontinuity, together with the chemical one in the [alpha /Fe] versus [Fe/H] diagram, and with the inferred age distributions, not only confirms the different chemo-dynamical histories of the chemical-thick and thin discs, but it is also suggestive of a halt in the star formation (quenching) after the formation of the chemical-thick disc. We then exploit the almost coeval alpha -rich population to gain insight into processes that may have altered the mass of a star along its evolution, which are key to improving the mapping of the current, observed, stellar mass to the initial mass and thus to the age. Comparing the mass distribution of stars on the lower RGB (R< 11 R-circle dot) with those in the red clump (RC), we find evidence for a mean integrated RGB mass loss Delta M = 0.10 +/- 0.02 M-circle dot. Finally, we find that the occurrence of massive (M greater than or similar to 1.1 M-circle dot) alpha -rich stars is of the order of 5% on the RGB, and significantly higher in the RC, supporting the scenario in which most of these stars had undergone an interaction with a companion.
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