Age dating of an early Milky Way merger via asteroseismology of the naked-eye star nu Indi
Safari, Hossein/0000-0003-2326-3201; Moya, Andres/0000-0003-1665-5389; Szabo, Robert/0000-0002-3258-1909; Serenelli, Aldo/0000-0001-6359-2769; Mazumdar, Anwesh/0000-0003-2409-2942; Handberg, Rasmus/0000-0001-8725-4502; Lysgaard Rorsted, Jakob/0000-0001-9234-430X; Lund, Mikkel Norup/0000-0001-9214-5642; Christensen-Dalsgaard, Jorgen/0000-0001-5137-0966; YILDIZ, Mutlu/0000-0002-7772-7641; Stokholm, Amalie/0000-0002-5496-365X; Verma, Kuldeep/0000-0003-0970-6440; Bazot, Michael/0000-0003-0166-1540; Lundkvist, Mia Sloth/0000-0002-8661-2571 ; WOS: 000508167700003 ; Over the course of its history, the Milky Way has ingested multiple smaller satellite galaxies1. Although these accreted stellar populations can be forensically identified as kinematically distinct structures within the Galaxy, it is difficult in general to date precisely the age at which any one merger occurred. Recent results have revealed a population of stars that were accreted via the collision of a dwarf galaxy, called Gaia-Enceladus1, leading to substantial pollution of the chemical and dynamical properties of the Milky Way. Here we identify the very bright, naked-eye star. Indi as an indicator of the age of the early in situ population of the Galaxy. We combine asteroseismic, spectroscopic, astrometric and kinematic observations to show that this metal-poor, alpha-element-rich star was an indigenous member of the halo, and we measure its age to be 11.0 +/- 0.7 (stat) +/- 0.8 (sys) billion years. the star bears hallmarks consistent with having been kinematically heated by the Gaia-Enceladus collision. Its age implies that the earliest the merger could have begun was 11.6 and 13.2 billion years ago, at 68% and 95% confidence, respectively. Computations based on hierarchical cosmological models slightly reduce the above limits. ; NASA High-End Computing (HEC) Program through the NASA Advanced Supercomputing (NAS) Division at Ames Research Center; UK Science and Technology Facilities Council (STFC)Science & Technology Facilities Council (STFC); UK Space Agency; Danish National Research FoundationDanmarks Grundforskningsfond [DNRF106]; National Science FoundationNational Science Foundation (NSF) [NSF PHY-1748958, AST-1903828, AST-1717000]; ERCEuropean Research Council (ERC) [772293]; Center for Cosmology and AstroParticle Physics at the Ohio State UniversityOhio State University; NYU Abu Dhabi Center for Space Science [G1502]; Spanish GovernmentSpanish Government [ESP2017-82674-R]; Generalitat de CatalunyaGeneralitat de Catalunya [2017-SGR-1131]; BelspoBelgian Federal Science Policy Office; European Social Fund via the Lithuanian Science Council [09.3.3-LMT-K-71201-0103]; NSFNational Science Foundation (NSF) [AST-1514676]; NASANational Aeronautics & Space Administration (NASA) [NNX16AB76G, 80NSSC19K0374, NAS5-26555]; Independent Research Fund Denmark [7027-00096B]; National Aeronautics and Space Administration through the TESS Guest Investigator Program [80NSSC18K1585, 80NSSC19K0379]; Max Planck Institute for Solar System Research; European UnionEuropean Union (EU) [749962, 792848, 664931]; FCT/MCTES through national funds (PIDDAC) [UID/FIS/04434/2019]; European Research Council under the European CommunityEuropean Research Council (ERC) [338251]; MINECO FPI-SO [SEV-2015-0548-17-2, BES2017-082610]; German space agency (Deutsches Zentrum fur Luft-und Raumfahrt) under PLATO data grant [50OO1501]; UK Science and Technology Facilities Council (STFC)Science & Technology Facilities Council (STFC) [ST/L000733/1]; Carlsberg FoundationCarlsberg Foundation [CF17-076]; Scientific and Technological Research Council of TurkeyTurkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [TUBITAK:118F352]; Spanish ministry through the Ramon y Cajal fellowship [RYC-2015-17697]; Premiale 2015 MITiC; NKFIH [K-115709]; Lendulet program of the Hungarian Academy of Science [20187/2019]; NASA through the NASA Hubble Fellowship - Space Telescope Science Institute [51424]; FEDER through COMPETE2020 [POCI-01-0145-FEDER-030389]; Government of India, Department of Atomic EnergyDepartment of Atomic Energy (DAE) [12-RD-TFR-6.04-0600] ; This paper includes data collected by the TESS mission, which are publicly available from the Mikulski Archive for Space Telescopes (MAST). Resources supporting this work were provided by the NASA High-End Computing (HEC) Program through the NASA Advanced Supercomputing (NAS) Division at Ames Research Center for the production of the SPOC data products. W.J.C. acknowledges support from the UK Science and Technology Facilities Council (STFC) and UK Space Agency. Funding for the Stellar Astrophysics Centre is provided by the Danish National Research Foundation (grant agreement number DNRF106). This research was partially conducted during the Exostar19 programme at the Kavli Institute for Theoretical Physics at UC Santa Barbara, which was supported in part by the National Science Foundation under grant number NSF PHY-1748958. A.M., J.T.M., F.V. and J.M. acknowledge support from the ERC Consolidator Grant funding scheme (project ASTEROCHRONOMETRY, grant agreement number 772293). F.V. acknowledges the support of a Fellowship from the Center for Cosmology and AstroParticle Physics at the Ohio State University. W.H.B. and M.B.N. acknowledge support from the UK Space Agency. K.J.B. is supported by the National Science Foundation under award AST-1903828. M.B.N. acknowledges partial support from the NYU Abu Dhabi Center for Space Science under grant number G1502. A.M.S. is partially supported by the Spanish Government (ESP2017-82674-R) and Generalitat de Catalunya (2017-SGR-1131). T.M. acknowledges financial support from Belspo for contract PRODEX PLATO. H.K. acknowledges support from the European Social Fund via the Lithuanian Science Council grant number 09.3.3-LMT-K-71201-0103. S.B. acknowledges support from NSF grant AST-1514676 and NASA grant 80NSSC19K0374. V.S.A. acknowledges support from the Independent Research Fund Denmark (research grant 7027-00096B). D.H. acknowledges support by the National Aeronautics and Space Administration (80NSSC18K1585, 80NSSC19K0379) awarded through the TESS Guest Investigator Program and by the National Science Foundation (AST-1717000). T.S.M. acknowledges support from a visiting fellowship at the Max Planck Institute for Solar System Research. Computational resources were provided through XSEDE allocation TG-AST090107. D.L.B. acknowledges support from NASA under grant NNX16AB76G. T.L.C. acknowledges support from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement number 792848 (PULSATION). This work was supported by FCT/MCTES through national funds (PIDDAC) by means of grant UID/FIS/04434/2019. K.J.B., S.H., J.S.K. and N.T. are supported by the European Research Council under the European Community's Seventh Framework Programme (FP7/2007-2013)/ERC grant agreement number 338251 (StellarAges). E.C. is funded by the European Union's Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement number 664931. L.G.-C. acknowledges support from the MINECO FPI-SO doctoral research project SEV-2015-0548-17-2 and predoctoral contract BES2017-082610. P.G. is supported by the German space agency (Deutsches Zentrum fur Luft-und Raumfahrt) under PLATO data grant 50OO1501. R.K. acknowledges support from the UK Science and Technology Facilities Council (STFC), under consolidated grant ST/L000733/1. M.S.L. is supported by the Carlsberg Foundation (grant agreement number CF17-076). Z.C.O., S.O. and M.Y. acknowledge support from the Scientific and Technological Research Council of Turkey (TUBITAK:118F352). S.M.; acknowledges support from the Spanish ministry through the Ramon y Cajal fellowship number RYC-2015-17697. T.S.R. acknowledges financial support from Premiale 2015 MITiC (PI B. Garilli). R.Sz. acknowledges the support from NKFIH grant project No. K-115709, and the Lendulet program of the Hungarian Academy of Science (project number 20187/2019). J.T. acknowledges support was provided by NASA through the NASA Hubble Fellowship grant number 51424 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555. This work was supported by FEDER through COMPETE2020 (POCI-01-0145-FEDER-030389. A.M.B. acknowledges funding from the European Union's Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement No 749962 (project THOT). A.M. and P.R. acknowledge the support of the Government of India, Department of Atomic Energy, under Project No. 12-R&D-TFR-6.04-0600. K.J.B. is an NSF Astronomy and Astrophysics Postdoctoral Fellow and DIRAC Fellow.