The GALAH survey: accreted stars also inhabit the Spite plateau

Author:

Simpson Jeffrey D12ORCID,Martell Sarah L12ORCID,Buder Sven23ORCID,Bland-Hawthorn Joss24ORCID,Casey Andrew R25ORCID,De Silva Gayandhi M67,D’Orazi Valentina8,Freeman Ken C23,Hayden Michael24,Kos Janez9,Lewis Geraint F4ORCID,Lind Karin10,Schlesinger Katharine J3,Sharma Sanjib24ORCID,Stello Dennis124,Zucker Daniel B2711,Zwitter Tomaž9ORCID,Asplund Martin12,Da Costa Gary23ORCID,Čotar Klemen9,Tepper-García Thor2413,Horner Jonathan14ORCID,Nordlander Thomas23ORCID,Ting Yuan-Sen3151617,Wyse Rosemary F G18ORCID,

Affiliation:

1. School of Physics, UNSW, Sydney, NSW 2052, Australia

2. Centre of Excellence for Astrophysics in Three Dimensions (ASTRO-3D), Australia

3. Research School of Astronomy and Astrophysics, Australian National University, ACT 2611, Canberra, Australia

4. Sydney Institute for Astronomy, School of Physics (A28), The University of Sydney, Sydney, NSW 2006, Australia

5. School of Physics and Astronomy, Monash University, Clayton, VIC 3800, Australia

6. Australian Astronomical Optics, Faculty of Science and Engineering, Macquarie University, Macquarie Park, NSW 2113, Australia

7. Macquarie University Research Centre for Astronomy, Astrophysics & Astrophotonics, Sydney, NSW 2109, Australia

8. Istituto Nazionale di Astrofisica, Osservatorio Astronomico di Padova, vicolo dell’Osservatorio 5, I-35122 Padova, Italy

9. Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000 Ljubljana, Slovenia

10. Department of Astronomy, Stockholm University, AlbaNova University Centre, SE-106 91 Stockholm, Sweden

11. Department of Physics and Astronomy, Macquarie University, Sydney, NSW 2109, Australia

12. Max Planck Institute for Astrophysics, Karl-Schwarzschild-Str 1, D-85741 Garching, Germany

13. Centre for Integrated Sustainability Analysis, The University of Sydney, Australia

14. Centre for Astrophysics, University of Southern Queensland, Toowoomba, QLD 4350, Australia

15. Institute for Advanced Study, Princeton, NJ 08540, USA

16. Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA

17. Observatories of the Carnegie Institution of Washington, 813 Santa Barbara Street, Pasadena, CA 91101, USA

18. Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218, USA

Abstract

ABSTRACT The European Space Agency (ESA) Gaia mission has enabled the remarkable discovery that a large fraction of the stars near the solar neighbourhood are debris from a single in-falling system, the so-called Gaia-Sausage-Enceladus (GSE). This discovery provides astronomers for the first time with a large cohort of easily observable, unevolved stars that formed in a single extragalactic environment. Here we use these stars to investigate the ‘Spite plateau’ – the near-constant lithium abundance observed in unevolved metal-poor stars across a wide range of metallicities (−3 < [Fe/H] < −1). Our aim is to test whether individual galaxies could have different Spite plateaus – e.g. the interstellar medium could be more depleted in lithium in a lower galactic mass system due to it having a smaller reservoir of gas. We identified 93 GSE dwarf stars observed and analysed by the GALactic Archaeology with HERMES (GALAH) survey as part of its Data Release 3 (DR3). Orbital actions were used to select samples of GSE stars, and comparison samples of halo and disc stars. We find that the GSE stars show the same lithium abundance as other likely accreted stars and in situ Milky Way stars. Formation environment leaves no imprint on lithium abundances. This result fits within the growing consensus that the Spite plateau, and more generally the ‘cosmological lithium problem’ – the observed discrepancy between the amount of lithium in warm, metal-poor dwarf stars in our Galaxy, and the amount of lithium predicted to have been produced by big bang nucleosynthesis – is the result of lithium depletion processes within stars.

Funder

Anglo-Australian Telescope

European Space Agency

Australian Research Council

JDS

UNSW

European Research Council

Horizon 2020 Framework Programme

NASA

Space Telescope Science Institute

ARC

Publisher

Oxford University Press (OUP)

Subject

Space and Planetary Science,Astronomy and Astrophysics

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