First GALAH data release

Spectroscopic surface gravity and effective temperature for 9860 Tycho-2 stars in GALAH (Martell et al. 2016)

Today is the first public data release for the GALAH (Galactic Archaeology with HERMES) Survey, a massive observational project that will study the history of star formation, chemical enrichment, radial migration and minor mergers in the Milky Way. GALAH has been observing since late 2013, and has collected spectra for over 250,000 Milky Way stars to date, with an ultimate goal of one million stars. GALAH uses the HERMES spectrograph at the Anglo-Australian Telescope to collect data for nearly 400 stars simultaneously in an observing program that uses 70 nights per year.

There are a number of large-scale Galactic archaeology studies that are currently ongoing, each with its own particular niche. GALAH's specialty is the Galactic disk: we expect 75% of the final GALAH data set to belong to the thin disk and 24% to the thick disk, and we will measure abundances for as many as 29 elements for each star we observe. However, it's the combination of large survey data sets where the real scientific power lies. As an example, combining the spectroscopic surveys gives abundance patterns and radial velocities for stars in the Galaxy from the Bulge through the Solar neighbourhood out to the halo, a comprehensive sample that no single survey can provide.

Combining spectroscopic data like GALAH with astrometry from the Gaia mission enables a whole range of new science based on chemodynamical information. GALAH stars are all in the magnitude range (12 < V < 14) for which Gaia parallaxes and proper motions will be at their best and most complete. Ultimately GALAH will be able to contribute elemental abundances for a large number of stars with high-precision Gaia data, forming a very powerful resource for studying Galactic structure and evolution. The first Gaia data release will be next week, on 14 September. It will include positions and G magnitudes for over a billion targets, and also parallaxes and proper motions for over 2 million Gaia stars that were also in the Hipparcos and Tycho-2 catalogues (the "TGAS" data set).

For this first GALAH data release we have selected 9860 stars that are likely to be included in the first Gaia data release as part of this TGAS data set, to help maximise the science the community can do with Gaia DR1 and to demonstrate the quality of GALAH derived quantities with a data set that will be extremely well studied in the near future. A paper describing GALAH's observational strategy and progress is on today's astro-ph at http://arxiv.org/abs/1609.02822, and the GALAH+TGAS catalogue with its explanatory ReadMe file can be downloaded from http://bit.ly/2crGk4O.

For more on the upcoming Gaia data release, please visit http://www.cosmos.esa.int/web/gaia/dr1.