GALAH Survey: Chemical tagging and disk reconstruction

The GALAH survey is now in its second year of a five‐year campaign to observe roughly one million stars in the southern hemisphere down to a limiting magnitude of V = 14. The project exploits the HERMES 400‐fibre échelle spectrograph at the Anglo‐Australian Telescope to measure up to 30 elemental abundances and radial velocities (≈1 km s –1 accuracy) for each star at a resolution of R = 28000. These elements fall into 8 independent groups (e.g. α , Fe peak, s‐process). For all GALAH stars, Gaia will provide distances to 1 % and transverse velocities to 1 km s –1 or better, giving us a 14D set of parameters for each star, i.e. 6D phase space and 8D abundance space. A few percent of GALAH stars will also have Kepler K2 seismological data. Here we focus on the prospect of chemically tagging the old stellar disk and making a direct measurement of how stellar migration evolves with cosmic time.