Age dissection of the Milky Way discs: Red giants in the Kepler field

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DOI

  • A. Miglio, University of Birmingham, INAF—OAS Osservatorio di Astrofisica e Scienza dello Spazio di Bologna
  • ,
  • C. Chiappini, Leibniz Institute for Astrophysics Potsdam
  • ,
  • J. T. MacKereth, University of Birmingham
  • ,
  • G. R. Davies, University of Birmingham
  • ,
  • K. Brogaard
  • L. Casagrande, Australian National University, ARC Centre of Excellence for All Sky Astrophysics in Three Dimensions (ASTRO-3D)
  • ,
  • W. J. Chaplin, University of Birmingham
  • ,
  • L. Girardi, Astronomical Observatory of Padua
  • ,
  • D. Kawata, University College London
  • ,
  • S. Khan, University of Birmingham
  • ,
  • R. Izzard, University of Surrey
  • ,
  • J. Montalbán, University of Birmingham
  • ,
  • B. Mosser, Sorbonne Université
  • ,
  • F. Vincenzo, University of Birmingham, Ohio State University
  • ,
  • D. Bossini, Universidade do Porto
  • ,
  • A. Noels, Universitè de Liège
  • ,
  • T. Rodrigues, INAF - Osservatorio Astronomico di Padova
  • ,
  • M. Valentini, Leibniz Institute for Astrophysics Potsdam
  • ,
  • I. Mandel, University of Birmingham, ARC Centre of Excellence for All Sky Astrophysics in Three Dimensions (ASTRO-3D), ARC Centre of Excellence for Gravitational Wave Discovery, Monash University

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 [α/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-[α/Fe], super-solar metallicity stars, reminiscent of the age and metallicity of the well-studied open clusterNGC 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 α-element-rich red-giant-branch (RGB) stars in our sample are compatible with those of an old (∼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 ∼1.5 Gyr. Moreover, we find a difference in the vertical velocity dispersion between low- and high-[α/Fe] populations. This discontinuity, together with the chemical one in the [α/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 α-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) with those in the red clump (RC), we find evidence for a mean integrated RGB mass loss ΔM»= 0.10... ±... 0.02 M. Finally, we find that the occurrence of massive (M"1.1 M) α-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.

OriginalsprogEngelsk
ArtikelnummerA85
TidsskriftAstronomy and Astrophysics
Vol/bind645
ISSN0004-6361
DOI
StatusUdgivet - jan. 2021

Bibliografisk note

Funding Information:
Acknowledgements. AM, JTM, JM, and FV acknowledge support from the ERC Consolidator Grant funding scheme (project ASTEROCHRONOMETRY, https://www.asterochronometry.eu, G.A. n. 772293). GRD has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (CartographY GA. 804752). FV acknowledges the support of a Fellowship from the Center for Cosmology and AstroParticle Physics at The Ohio State University. AM, GRD, and WJC acknowledge the support of the UK Science and Technology Facilities Council (STFC). We are extremely grateful to the International Space Science Institute (ISSI) for support provided to the asterosSTEP ISSI International Team (http://www.issibern.ch/teams/asterostep/). DB is supported in the form of work contract FCT/MCTES through national funds and by FEDER through COMPETE2020 in connection to these grants: UID/FIS/04434/2019; PTDC/FIS-AST/30389/2017 & POCI-01-0145-FEDER-030389. LC is the recipient of the ARC Future Fellowship FT160100402. Parts of this research were conducted by the ARC Centre of Excellence ASTRO 3D, through project number CE170100013. IM is a recipient of the Australian Research Council Future Fellowship FT190100574. CC acknowledges partial support from DFG Grant CH1188/2-1 and from the ChETEC COST Action (CA16117), supported by COST (European Cooperation in Science and Technology). We thank Maurizio Salaris for many useful discussions and Will Farr for providing suggestions on the statistical models. This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www. cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/ consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. This paper includes data collected by the Kepler mission. Funding for the Kepler mission is provided by the NASA Science Mission directorate. Funding for the Sloan Digital Sky Survey IV has been provided by the Alfred P. Sloan Foundation, the US Department of Energy Office of Science, and the Participating Institutions. SDSS acknowledges support and resources from the Center for High-Performance Computing at the University of Utah. The SDSS web site is www.sdss.org. SDSS is managed by the Astrophysical Research Consortium for the Participating Institutions of the SDSS Collaboration including the Brazilian Participation Group, the Carnegie Institution for Science, Carnegie Mellon University, the Chilean Participation Group, the French Participation Group, Harvard-Smithsonian Center for Astrophysics, Instituto de Astrofísica de Canarias, The Johns Hopkins University, Kavli Institute for the Physics and Mathematics of the Universe (IPMU)/University of Tokyo, the Korean Participation Group, Lawrence Berkeley National Laboratory, Leibniz Institut für Astrophysik Potsdam (AIP), Max-Planck-Institut für Astronomie (MPIA Heidelberg), Max-Planck-Institut für Astrophysik (MPA Garching), Max-Planck-Institut für Extraterrestrische Physik (MPE), National Astronomical Observatories of China, New Mexico State University, New York University, University of Notre Dame, Observatório Nacional/MCTI, The Ohio State University, Pennsylvania State University, Shanghai Astronomical Observatory, United Kingdom Participation Group, Universidad Nacional Autónoma de México, 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, and Yale University. The computations described in this paper were performed using the University of Birmingham’s BlueBEAR HPC service, which provides a High Performance Computing service to the University’s research community. See http://www.birmingham.ac.uk/bear for more details.

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© 2021 ESO.

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Copyright 2021 Elsevier B.V., All rights reserved.

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