The GALAH survey: temporal chemical enrichment of the galactic disc

Jane Lin*, Martin Asplund, Yuan Sen Ting, Luca Casagrande, Sven Buder, Joss Bland-Hawthorn, Andrew R. Casey, Gayandhi M. de Silva, Valentina D'Orazi, Ken C. Freeman, Janez Kos, K. Lind, Sarah L. Martell, Sanjib Sharma, Jeffrey D. Simpson, Tomaž Zwitter, Daniel B. Zucker, Ivan Minchev, Klemen Čotar, Michael HaydenJonti Horner, Geraint F. Lewis, Thomas Nordlander, Rosemary F.G. Wyse, Maruša Žerjal

*Corresponding author for this work

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Abstract

We present isochrone ages and initial bulk metallicities ([Fe/H]bulk, by accounting for diffusion) of 163 722 stars from the GALAH Data Release 2, mainly composed of main-sequence turn-off stars and subgiants (7000 K > Teff > 4000 K and log g > 3 dex). The local age-metallicity relationship (AMR) is nearly flat but with significant scatter at all ages; the scatter is even higher when considering the observed surface abundances. After correcting for selection effects, the AMR appears to have intrinsic structures indicative of two star formation events, which we speculate are connected to the thin and thick discs in the solar neighbourhood. We also present abundance ratio trends for 16 elements as a function of age, across different [Fe/H]bulk bins. In general, we find the trends in terms of [X/Fe] versus age from our far larger sample to be compatible with studies based on small (∼100 stars) samples of solar twins, but we now extend them to both sub- and supersolar metallicities. The α-elements show differing behaviour: the hydrostatic α-elements O and Mg show a steady decline with time for all metallicities, while the explosive α-elements Si, Ca, and Ti are nearly constant during the thin-disc epoch (ages ≲ 12 Gyr). The s-process elements Y and Ba show increasing [X/Fe] with time while the r-process element Eu has the opposite trend, thus favouring a primary production from sources with a short time delay such as core-collapse supernovae over long-delay events such as neutron star mergers.

Original languageEnglish
Pages (from-to)2043-2056
Number of pages14
JournalMonthly Notices of the Royal Astronomical Society
Volume491
Issue number2
DOIs
Publication statusPublished - Jan 2020

Bibliographical note

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society, Volume 491, Issue 2, January 2020, Pages 2043–2056, https://doi.org/10.1093/mnras/stz3048. Copyright 2019 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

Keywords

  • Solar neighbourhood
  • Stars: abundances
  • Stars: fundamental parameters

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