TY - JOUR
T1 - The GALAH survey
T2 - temporal chemical enrichment of the galactic disc
AU - Lin, Jane
AU - Asplund, Martin
AU - Ting, Yuan Sen
AU - Casagrande, Luca
AU - Buder, Sven
AU - Bland-Hawthorn, Joss
AU - Casey, Andrew R.
AU - de Silva, Gayandhi M.
AU - D'Orazi, Valentina
AU - Freeman, Ken C.
AU - Kos, Janez
AU - Lind, K.
AU - Martell, Sarah L.
AU - Sharma, Sanjib
AU - Simpson, Jeffrey D.
AU - Zwitter, Tomaž
AU - Zucker, Daniel B.
AU - Minchev, Ivan
AU - Čotar, Klemen
AU - Hayden, Michael
AU - Horner, Jonti
AU - Lewis, Geraint F.
AU - Nordlander, Thomas
AU - Wyse, Rosemary F.G.
AU - Žerjal, Maruša
N1 - 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.
PY - 2020/1
Y1 - 2020/1
N2 - 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.
AB - 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.
KW - Solar neighbourhood
KW - Stars: abundances
KW - Stars: fundamental parameters
UR - http://www.scopus.com/inward/record.url?scp=85079661987&partnerID=8YFLogxK
UR - http://purl.org/au-research/grants/arc/CE170100013
U2 - 10.1093/mnras/stz3048
DO - 10.1093/mnras/stz3048
M3 - Article
AN - SCOPUS:85079661987
VL - 491
SP - 2043
EP - 2056
JO - Monthly Notices of the Royal Astronomical Society: Letters
JF - Monthly Notices of the Royal Astronomical Society: Letters
SN - 1745-3925
IS - 2
ER -