Age dating of an early Milky Way merger via asteroseismology of the naked-eye star $ν$ Indi
Creators: name: Chaplin, William J.
name: Serenelli, Aldo M.
name: Miglio, Andrea
name: Morel, Thierry
name: Mackereth, J. Ted
name: Vincenzo, Fiorenzo
name: Basu, Hans Kjeldsen Sarbani
name: Ball, Warrick H.
name: Stokholm, Amalie
name: Verma, Kuldeep
name: Mosumgaard, Jakob Rørsted
name: Aguirre, Victor Silva
name: Mazumdar, Anwesh
name: Ranadive, Pritesh
name: Antia, H. M.
name: Lebreton, Yveline
name: Ong, Joel
name: Appourchaux, Thierry
name: Bedding, Timothy R.
name: Christensen-Dalsgaard, Jørgen
name: Creevey, Orlagh
name: García, Rafael A.
name: Handberg, Rasmus
name: Huber, Daniel
name: Kawaler, Steven D.
name: Lund, Mikkel N.
name: Metcalfe, Travis S.
name: Stassun, Keivan G.
name: Bazot, Michäel
name: Beck, Paul
name: Bell, Keaton J.
name: Bergemann, Maria
name: Buzasi, Derek L.
name: Benomar, Othman
name: Bossini, Diego
name: Bugnet, Lisa
name: Campante, Tiago L.
name: Orhan, Zeynep Çelik
name: Corsaro, Enrico
name: González-Cuesta, Lucía
name: Davies, Guy R.
name: Di Mauro, Maria Pia
name: Egeland, Ricky
name: Elsworth, Yvonne P.
name: Gaulme, Patrick
name: Ghasemi, Hamed
name: Guo, Zhao
name: Hall, Oliver J.
name: Hasanzadeh, Amir
name: Hekker, Saskia
name: Howe, Rachel
name: Jenkins, Jon M.
name: Jiménez, Antonio
name: Kiefer, René
name: Kuszlewicz, James S.
name: Kallinger, Thomas
name: Latham, David W.
name: Lundkvist, Mia S.
name: Mathur, Savita
name: Montalbán, Josefina
name: Mosser, Benoit
name: Bedón, Andres Moya
name: Nielsen, Martin Bo
name: Örtel, Sibel
name: Rendle, Ben M.
name: Ricker, George R.
name: Rodrigues, Thaíse S.
name: Roxburgh, Ian W.
name: Safari, Hossein
name: Schofield, Mathew
name: Seager, Sara
name: Smalley, Barry
name: Stello, Dennis
name: Szabó, Róbert
name: Tayar, Jamie
name: Themeßl, Nathalie
name: Thomas, Alexandra E. L.
name: Vanderspek, Roland K.
name: van Rossem, Walter E.
name: Vrard, Mathieu
name: Weiss, Achim
name: White, Timothy R.
name: Winn, Joshua N.
name: Yıldız, Mutlu
Publisher: name: arXiv
Year: 2020
Subjects: subject: Astrophysics of Galaxies (astro-ph.GA)
subject: Solar and Stellar Astrophysics (astro-ph.SR)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: Over the course of its history, the Milky Way has ingested multiple smaller satellite galaxies. While these accreted stellar populations can be forensically identified as kinematically distinct structures within the Galaxy, it is difficult in general to precisely date 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 \textit{Gaia}-Enceladus, leading to a substantial pollution of the chemical and dynamical properties of the Milky Way. Here, we identify the very bright, naked-eye star $ν$\,Indi as a probe 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 $11.0 \pm 0.7$ (stat) $\pm 0.8$ (sys)$\,\rm Gyr$. The star bears hallmarks consistent with it having been kinematically heated by the \textit{Gaia}-Enceladus collision. Its age implies that the earliest the merger could have begun was 11.6 and 13.2 Gyr ago at 68 and 95% confidence, respectively. Input from computations based on hierarchical cosmological models tightens (i.e. reduces) slightly the above limits.
description: Accepted for publication as a Letter in Nature Astronomy (26 pages, 7 figures, including main article and methods section)