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The K2-HERMES Survey: age and metallicity of the thick disc
Univ Sydney, Sch Phys, Sydney Inst Astron, Sydney, NSW 2006, Australia;ARC Ctr Excellence All Sky Astrophys Three Dimens, Canberra, ACT 2611, Australia.
Univ Sydney, Sch Phys, Sydney Inst Astron, Sydney, NSW 2006, Australia;ARC Ctr Excellence All Sky Astrophys Three Dimens, Canberra, ACT 2611, Australia;Univ New South Wales, Sch Phys, Sydney, NSW 2052, Australia;Aarhus Univ, Dept Phys & Astron, Stellar Astrophys Ctr, Ny Munkegade 120, DK-8000 Aarhus C, Denmark.
Univ Sydney, Sch Phys, Sydney Inst Astron, Sydney, NSW 2006, Australia;ARC Ctr Excellence All Sky Astrophys Three Dimens, Canberra, ACT 2611, Australia.
Univ Sydney, Sch Phys, Sydney Inst Astron, Sydney, NSW 2006, Australia;ARC Ctr Excellence All Sky Astrophys Three Dimens, Canberra, ACT 2611, Australia.
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2019 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 490, no 4, p. 5335-5352Article in journal (Refereed) Published
Abstract [en]

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 oldmetal-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 [alpha/Fe] elemental abundances from the GALAH survey indicate a mean metallicity of log (Z/Z(circle dot)) = -0.16 for the thick disc. Here Z is the effective solar-scaled metallicity, which is a function of [Fe/H] and [alpha/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 alpha-enhanced thick disc.

Place, publisher, year, edition, pages
OXFORD UNIV PRESS , 2019. Vol. 490, no 4, p. 5335-5352
Keywords [en]
methods: data analysis, methods: numerical, Galaxy: stellar content, Galaxy: structure
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:uu:diva-402662DOI: 10.1093/mnras/stz2861ISI: 000504000300064OAI: oai:DiVA.org:uu-402662DiVA, id: diva2:1386951
Funder
Swedish Research Council, 2015-00415_3Available from: 2020-01-20 Created: 2020-01-20 Last updated: 2020-01-20Bibliographically approved

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