The GALAH survey: An abundance, age, and kinematic inventory of the solar neighbourhood made with TGAS^⋆

¹ Max Planck Institute for Astronomy (MPIA), Koenigstuhl 17, 69117 Heidelberg
e-mail: buder@mpia.de
² Department of Physics and Astronomy, Uppsala University, Box 516, 751 20 Uppsala, Sweden
³ Department of Astronomy, Columbia University, Pupin Physics Laboratories, New York, NY 10027, USA
⁴ Center for Computational Astrophysics, Flatiron Institute, 162 Fifth Avenue, New York, NY 10010, USA
⁵ Research School of Astronomy & Astrophysics, Mount Stromlo Observatory, Australian National University, ACT 2611, Australia
⁶ Center of Excellence for Astrophysics in Three Dimensions (ASTRO-3D), Australia
⁷ Sydney Institute for Astronomy (SIfA), School of Physics, A28, The University of Sydney, NSW 2006, Australia
⁸ Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000 Ljubljana, Slovenia
⁹ School of Physics and Astronomy, Monash University, Australia
¹⁰ Faculty of Information Technology, Monash University, Australia
¹¹ Department of Physics and Astronomy, Macquarie University, Sydney, NSW 2109, Australia
¹² Istituto Nazionale di Astrofisica, Osservatorio Astronomico di Padova, vicolo dell’Osservatorio 5, 35122 Padova, Italy
¹³ School of Physics, University of New South Wales, Sydney, NSW 2052, Australia
¹⁴ Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA
¹⁵ Western Sydney University, Locked Bag 1797, Penrith South, NSW 2751, Australia
¹⁶ ICRAR, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia
¹⁷ Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, MD 21218, USA
¹⁸ Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, 8000 Aarhus C, Denmark
¹⁹ Institute for Advanced Study, Princeton, NJ 08540, USA
²⁰ Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA
²¹ Observatories of the Carnegie Institution of Washington, 813 Santa Barbara Street, Pasadena, CA 91101, USA

Received: 12 April 2018
Accepted: 7 February 2019

Abstract

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 sub-giant 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 [α/Fe] of the magnitude-selected sample, we recover the result that stars of the high-α sequence are typically older than stars in the low-α sequence, the latter spanning iron abundances of −0.7 <  [Fe/H] <  +0.5. While these two sequences become indistinguishable in [α/Fe] vs. [Fe/H] at the metal-rich regime, we find that age can be used to separate stars from the extended high-α and the low-α 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-α-sequence up to super-solar [Fe/H] rather than a gap, which has been interpreted as a separate “high-α metal-rich” population. Stars in our sample that are younger than 10 Gyr, are mainly found on the low α-sequence and show a gradient in L_z from low [Fe/H] (L_z >  L_z, ⊙) towards higher [Fe/H] (L_z <  L_z, ⊙), which implies that the stars at the ends of this sequence are likely not originating from the close solar vicinity.