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Age dating of an early Milky Way merger via asteroseismology of the naked-eye star ν Indi

William Chaplin 1 Aldo Serenelli 2 Andrea Miglio 3 Thierry Morel 4 J. Ted Mackereth Fiorenzo Vincenzo Hans Kjeldsen 5 Sarbani Basu 6 Warrick Ball Amalie Stokholm Kuldeep Verma 7 Jakob Rørsted Mosumgaard Victor Silva Aguirre 8 Anwesh Mazumdar Pritesh Ranadive H. Antia Yveline Lebreton 9, 10 Joel Ong Thierry Appourchaux 11 Timothy Bedding 12 Jørgen Christensen-Dalsgaard 5 Orlagh Creevey 13 Rafael Garcia 14 Rasmus Handberg 15 Daniel Huber 12 Steven Kawaler 16 Mikkel Lund Travis Metcalfe Keivan Stassun Michaël Bazot 5 Paul Beck Keaton Bell Maria Bergemann Derek Buzasi Othman Benomar Diego Bossini Lisa Bugnet Tiago Campante Zeynep Çelik Orhan Enrico Corsaro 17 Lucía González-Cuesta Guy Davies Maria Pia Di Mauro 18 Ricky Egeland Yvonne Elsworth 3 Patrick Gaulme 19 Hamed Ghasemi Zhao Guo Oliver Hall Amir Hasanzadeh Saskia Hekker 3 Rachel Howe Jon Jenkins 20 Antonio Jiménez 21 René Kiefer 22 James Kuszlewicz 23 Thomas Kallinger 24 David Latham Mia Lundkvist Savita Mathur 25 Josefina Montalbán 26 Benoit Mosser 10 Andres Moya Bedón Martin Bo Nielsen Sibel Örtel Ben Rendle George Ricker 27 Thaíse Rodrigues Ian Roxburgh Hossein Safari Mathew Schofield Sara Seager Barry Smalley Dennis Stello 12 Róbert Szabó 28 Jamie Tayar 29 Nathalie Themeßl Alexandra Thomas Roland Vanderspek Walter van Rossem Mathieu Vrard 30 Achim Weiss 8 Timothy White Joshua Winn Mutlu Yıldız
Abstract : 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 ν 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.
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William Chaplin, Aldo Serenelli, Andrea Miglio, Thierry Morel, J. Ted Mackereth, et al.. Age dating of an early Milky Way merger via asteroseismology of the naked-eye star ν Indi. Nature Astronomy, Nature Publishing Group, 2020, 4 (4), pp.382-389. ⟨10.1038/s41550-019-0975-9⟩. ⟨obspm-02440136⟩

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