TY - JOUR
T1 - The K2-HERMES Survey
T2 - age and metallicity of the thick disc
AU - Sharma, Sanjib
AU - Stello, Dennis
AU - Bland-Hawthorn, Joss
AU - Hayden, Michael R.
AU - Zinn, Joel C.
AU - Kallinger, Thomas
AU - Hon, Marc
AU - Asplund, Martin
AU - Buder, Sven
AU - de Silva, Gayandhi M.
AU - D'Orazi, Valentina
AU - Freeman, Ken
AU - Kos, Janez
AU - Lewis, Geraint F.
AU - Lin, Jane
AU - Lind, Karin
AU - Martell, Sarah
AU - Simpson, Jeffrey D.
AU - Wittenmyer, Rob A.
AU - Zucker, Daniel B.
AU - Zwitter, Tomaz
AU - Bedding, Timothy R.
AU - Chen, Boquan
AU - Cotar, Klemen
AU - Esdaile, James
AU - Horner, Jonathan
AU - Huber, Daniel
AU - Kafle, Prajwal R.
AU - Khanna, Shourya
AU - Li, Tanda
AU - Ting, Yuan Sen
AU - Nataf, David M.
AU - Nordlander, Thomas
AU - Saadon, Mohd Hafiz Mohd
AU - Traven, Gregor
AU - Wright, Duncan
AU - Wyse, Rosemary F.G.
N1 - This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society, Volume 490, Issue 4, December 2019, Pages 5335–5352, https://doi.org/10.1093/mnras/stz2861. Copyright 2019 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
PY - 2019/12/1
Y1 - 2019/12/1
N2 - Asteroseismology is a promising tool to study Galactic structure and evolution because it can probe the ages of stars. Earlier attempts comparing seismic data from the Kepler satellite with predictions from Galaxy models found that the models predicted more low-mass stars compared to the observed distribution of masses. It was unclear if the mismatch was due to inaccuracies in the Galactic models, or the unknown aspects of the selection function of the stars. Using new data from the K2 mission, which has a well-defined selection function, we find that an old metal-poor thick disc, as used in previous Galactic models, is incompatible with the asteroseismic information. We use an importance-sampling framework, which takes the selection function into account, to fit for the metallicities of a population synthesis model using spectroscopic data. We show that spectroscopic measurements of [Fe/H] and [α/Fe] elemental abundances from the GALAH survey indicate a mean metallicity of log (Z/Z☉) = −0.16 for the thick disc. Here Z is the effective solar-scaled metallicity, which is a function of [Fe/H] and [α/Fe]. With the revised disc metallicities, for the first time, the theoretically predicted distribution of seismic masses show excellent agreement with the observed distribution of masses. This indirectly verifies that the asteroseismic mass scaling relation is good to within five per cent. Assuming the asteroseismic scaling relations are correct, we estimate the mean age of the thick disc to be about 10 Gyr, in agreement with the traditional idea of an old α-enhanced thick disc.
AB - Asteroseismology is a promising tool to study Galactic structure and evolution because it can probe the ages of stars. Earlier attempts comparing seismic data from the Kepler satellite with predictions from Galaxy models found that the models predicted more low-mass stars compared to the observed distribution of masses. It was unclear if the mismatch was due to inaccuracies in the Galactic models, or the unknown aspects of the selection function of the stars. Using new data from the K2 mission, which has a well-defined selection function, we find that an old metal-poor thick disc, as used in previous Galactic models, is incompatible with the asteroseismic information. We use an importance-sampling framework, which takes the selection function into account, to fit for the metallicities of a population synthesis model using spectroscopic data. We show that spectroscopic measurements of [Fe/H] and [α/Fe] elemental abundances from the GALAH survey indicate a mean metallicity of log (Z/Z☉) = −0.16 for the thick disc. Here Z is the effective solar-scaled metallicity, which is a function of [Fe/H] and [α/Fe]. With the revised disc metallicities, for the first time, the theoretically predicted distribution of seismic masses show excellent agreement with the observed distribution of masses. This indirectly verifies that the asteroseismic mass scaling relation is good to within five per cent. Assuming the asteroseismic scaling relations are correct, we estimate the mean age of the thick disc to be about 10 Gyr, in agreement with the traditional idea of an old α-enhanced thick disc.
KW - Galaxy: stellar content
KW - Galaxy: structure
KW - Methods: data analysis
KW - Methods: numerical
UR - http://www.scopus.com/inward/record.url?scp=85079617898&partnerID=8YFLogxK
U2 - 10.1093/mnras/stz2861
DO - 10.1093/mnras/stz2861
M3 - Article
AN - SCOPUS:85079617898
SN - 0035-8711
VL - 490
SP - 5335
EP - 5352
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
IS - 4
ER -