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

GALAH Collaboration

Research output: Contribution to journalArticle

3 Citations (Scopus)

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 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.

Original languageEnglish
Article number19
Number of pages30
JournalASTRONOMY & ASTROPHYSICS
Volume624
DOIs
Publication statusPublished - 2 Apr 2019

Cite this

@article{b370b5618de041f582f640eeaf8f1469,
title = "The GALAH survey: An abundance, age, and kinematic inventory of the solar neighbourhood made with TGAS",
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 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.",
keywords = "surveys, solar neighborhood, Galaxy: evolution, stars: fundamental parameters, stars: abundances, stars: kinematics and dynamics, GALACTIC CHEMICAL EVOLUTION, LTE LINE FORMATION, METAL-POOR STARS, OPEN CLUSTER M67, ISOTOPE RATIOS, IA SUPERNOVAE, NEARBY STARS, FAINT STARS, THICK, DISC",
author = "{GALAH Collaboration} and S. Buder and K. Lind and Ness, {M. K.} and M. Asplund and L. Duong and J. Lin and J. Kos and L. Casagrande and Casey, {A. R.} and J. Bland-Hawthorn and {De Silva}, {G. M.} and Valentina D'Orazi and Freeman, {K. C.} and Martell, {S. L.} and Schlesinger, {K. J.} and S. Sharma and Simpson, {J. D.} and Zucker, {D. B.} and T. Zwitter and K. Cotar and A. Dotter and Hayden, {M. R.} and Hyde, {E. A.} and Kafle, {P. R.} and Lewis, {G. F.} and Nataf, {D. M.} and T. Nordlander and W. Reid and H-W Rix and A. Skuladottir and D. Stello and Y-S Ting and G. Traven and Wyse, {R. F. G.}",
year = "2019",
month = "4",
day = "2",
doi = "10.1051/0004-6361/201833218",
language = "English",
volume = "624",
journal = "ASTRONOMY & ASTROPHYSICS",
issn = "0004-6361",
publisher = "EDP SCIENCES S A",

}

The GALAH survey : An abundance, age, and kinematic inventory of the solar neighbourhood made with TGAS. / GALAH Collaboration.

In: ASTRONOMY & ASTROPHYSICS, Vol. 624, 19, 02.04.2019.

Research output: Contribution to journalArticle

TY - JOUR

T1 - The GALAH survey

T2 - An abundance, age, and kinematic inventory of the solar neighbourhood made with TGAS

AU - GALAH Collaboration

AU - Buder, S.

AU - Lind, K.

AU - Ness, M. K.

AU - Asplund, M.

AU - Duong, L.

AU - Lin, J.

AU - Kos, J.

AU - Casagrande, L.

AU - Casey, A. R.

AU - Bland-Hawthorn, J.

AU - De Silva, G. M.

AU - D'Orazi, Valentina

AU - Freeman, K. C.

AU - Martell, S. L.

AU - Schlesinger, K. J.

AU - Sharma, S.

AU - Simpson, J. D.

AU - Zucker, D. B.

AU - Zwitter, T.

AU - Cotar, K.

AU - Dotter, A.

AU - Hayden, M. R.

AU - Hyde, E. A.

AU - Kafle, P. R.

AU - Lewis, G. F.

AU - Nataf, D. M.

AU - Nordlander, T.

AU - Reid, W.

AU - Rix, H-W

AU - Skuladottir, A.

AU - Stello, D.

AU - Ting, Y-S

AU - Traven, G.

AU - Wyse, R. F. G.

PY - 2019/4/2

Y1 - 2019/4/2

N2 - 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.

AB - 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.

KW - surveys

KW - solar neighborhood

KW - Galaxy: evolution

KW - stars: fundamental parameters

KW - stars: abundances

KW - stars: kinematics and dynamics

KW - GALACTIC CHEMICAL EVOLUTION

KW - LTE LINE FORMATION

KW - METAL-POOR STARS

KW - OPEN CLUSTER M67

KW - ISOTOPE RATIOS

KW - IA SUPERNOVAE

KW - NEARBY STARS

KW - FAINT STARS

KW - THICK

KW - DISC

U2 - 10.1051/0004-6361/201833218

DO - 10.1051/0004-6361/201833218

M3 - Article

VL - 624

JO - ASTRONOMY & ASTROPHYSICS

JF - ASTRONOMY & ASTROPHYSICS

SN - 0004-6361

M1 - 19

ER -