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

S. Buder, K. Lind, M. K. Ness, M. Asplund, L. Duong, J. Lin, J. Kos, L. Casagrande, J. Bland-Hawthorn, A. R. Casey, G. M. De Silva, V. D'Orazi, K. C. Freeman, G. F. Lewis, S. L. Martell, K. J. Schlesinger, S. Sharma, J. D. Simpson, D. B. Zucker, T. Zwitter, K. Cotar, A. Dotter, M. R. Hayden, E. A. Hyde, P. R. Kafle, D. M. Nataf, T. Nordlander, W. Reid, H. -W. Rix, A. Skuladottir, D. Stello, Y. -S. Ting, G. Traven, R. F. G. Wyse

Published 2018-04-16Version 1

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. Our stars span mainly metallicities $-0.7 < \mathrm{[Fe/H]} < +0.5$. We report measurements of Li, C, O, Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Y, and Ba and note that for some elements (Li, O, Al, and Fe), we employ non-LTE calculations. These elements represent several nucleosynthesis channels including $\alpha$, iron-peak, and s-process. We find strong correlations between stellar age and abundance, including for $\alpha$-elements and the s-process elements Y and Ba. Furthermore, in the high-$\alpha$ metal-rich regime, age can be used in combination with chemistry to separate stars from the extended high-$\alpha$ sequence and the low-$\alpha$ one. We find that the low-$\alpha$ metal-poor stars in the solar neighbourhood have significantly higher angular momentum $L_z$ than the Sun, which implies that they are on eccentric orbits and originate from the outer disk. Stars of the high-$\alpha$-sequence on the other hand have lower $L_z$ than the Sun, implying they are visitors from the inner disk.