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The GALAH survey: An abundance, age, and kinematic inventory of the solar neighbourhood made with TGAS
MPIA, Koenigstuhl 17, D-69117 Heidelberg, Germany;Heidelberg Univ, Int Max Planck Res Sch Astron & Cosm Phys, Heidelberg, Germany.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy. MPIA, Koenigstuhl 17, D-69117 Heidelberg, Germany.
Columbia Univ, Dept Astron, Pupin Phys Labs, New York, NY 10027 USA;Flatiron Inst, Ctr Computat Astrophys, 162 Fifth Ave, New York, NY 10010 USA.
Australian Natl Univ, Res Sch Astron & Astrophys, Mt Stromlo Observ, Weston, ACT 2611, Australia;Ctr Excellence Astrophys Three Dimens ASTRO 3D, Sydney, NSW, Australia.
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2019 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 624, article id A19Article in journal (Refereed) Published
Abstract [en]

The overlap between the spectroscopic Galactic Archaeology with HERMES (GALAH) survey and Gaia provides a high-dimensional chemodynamical space of unprecedented size. We present a first analysis of a subset of this overlap, of 7066 dwarf, turn-off, and subgiant stars. These stars have spectra from the GALAH survey and high parallax precision from the Gaia DR1 Tycho-Gaia Astrometric Solution. We investigate correlations between chemical compositions, ages, and kinematics for this sample. Stellar parameters and elemental abundances are derived from the GALAH spectra with the spectral synthesis code SPECTROSCOPY MADE EASY. We determine kinematics and dynamics, including action angles, from the Gaia astrometry and GALAH radial velocities. Stellar masses and ages are determined with Bayesian isochrone matching, using our derived stellar parameters and absolute magnitudes. We report measurements of Li, C, O, Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Y, as well as Ba and we note that we have employed non-LTE calculations for Li, O, Al, and Fe. We show that the use of astrometric and photometric data improves the accuracy of the derived spectroscopic parameters, especially log g. Focusing our investigation on the correlations between stellar age, iron abundance [Fe/H], and mean alpha-enhancement [alpha/Fe] of the magnitude-selected sample, we recover the result that stars of the high-a sequence are typically older than stars in the low-a sequence, the latter spanning iron abundances of -0.7 < [Fe/H] < +0.5. While these two sequences become indistinguishable in [alpha/Fe] vs. [Fe/H] at the metal-rich regime, we find that age can be used to separate stars from the extended high-a and the low-a sequence even in this regime. When dissecting the sample by stellar age, we find that the old stars (>8 Gyr) have lower angular momenta L-z than the Sun, which implies that they are on eccentric orbits and originate from the inner disc. Contrary to some previous smaller scale studies we find a continuous evolution in the high-alpha-sequence up to super-solar [Fe/H] rather than a gap, which has been interpreted as a separate "high-alpha metal-rich" population. Stars in our sample that are younger than 10 Gyr, are mainly found on the low alpha-sequence and show a gradient in L-z from low [Fe/H] > (L-z > L-z,L-circle dot) towards higher [Fe/H] (L-z < L-z,L-circle dot), which implies that the stars at the ends of this sequence are likely not originating from the close solar vicinity.

Place, publisher, year, edition, pages
EDP SCIENCES S A , 2019. Vol. 624, article id A19
Keywords [en]
surveys, solar neighborhood, Galaxy: evolution, stars: fundamental parameters, stars: abundances, stars: kinematics and dynamics
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:uu:diva-382390DOI: 10.1051/0004-6361/201833218ISI: 000462979700002OAI: oai:DiVA.org:uu-382390DiVA, id: diva2:1307168
Funder
Swedish Research Council, 2015-00415_3Australian Research Council, DE1401000598Swedish National Infrastructure for Computing (SNIC), 2015/1-309Swedish National Infrastructure for Computing (SNIC), 2016/1-400Available from: 2019-04-26 Created: 2019-04-26 Last updated: 2019-04-26Bibliographically approved

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