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

TL;DR

This study utilizes GALAH and Gaia data to analyze the chemical, age, and kinematic properties of over 7,000 stars in the solar neighborhood, revealing correlations between stellar populations, ages, and orbital characteristics.

Contribution

It provides a comprehensive chemodynamical analysis of a large stellar sample, incorporating non-LTE calculations and improved parameter accuracy, and clarifies the relationship between stellar populations and their origins.

Findings

High-$ m extalpha$ stars are generally older than low-$ m extalpha$ stars.

A continuous evolution in the high-$ m extalpha$ sequence up to super-solar metallicity.

Old stars have lower angular momentum, indicating inner disk origins.

Abstract

The overlap between the spectroscopic Galactic Archaeology with HERMES (GALAH) survey & $Gaia$ 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, & sub-giant stars. [...] We investigate correlations between chemical compositions, ages, & kinematics for this sample. Stellar parameters & elemental abundances are derived from the GALAH spectra with the spectral synthesis code SME. [...] We report Li, C, O, Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Y, as well as Ba & we note that we employ non-LTE calculations for Li, O, Al, & Fe. We show that the use of astrometric & photometric data improves the accuracy of the derived spectroscopic parameters, especially $\log g$. [...] we recover the result that stars of the high-$\alpha$ sequence are typically older than stars in the low-$\alpha$ sequence, the latter spanning $-0.7<$[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-$\alpha$ & the low-$\alpha$ sequence even in this regime. [...] 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 & originate from the inner disk. 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 & show a gradient in $L_z$ from low [Fe/H] ($L_z>L_{z,\odot}$) towards higher [Fe/H] ($L_z<L_{z,\odot}$), which implies that the stars at the ends of this sequence are likely not originating from the close solar vicinity.