We implement Gaia and 2MASS photometry in the InfraRed Flux Method and apply it to stars across different evolutionary status in the GALAH DR3 survey. We derive colour-effective temperature relations that take into account the effect of metallicity and surface gravity over the range 3600 - 9000 K. Comparison against solar-twins, Gaia benchmark stars and the latest interferometric measurements validates the precision and accuracy of these calibrations for spectral types later than F. We assess the impact of various sources of uncertainties and provide guidelines to use our relations.

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colte.pdf

We explore the fundamental relations governing the radial and vertical velocity dispersions of stars in the Milky Way. We determine stellar age estimates from combined studies of complementary surveys including GALAH, LAMOST, APOGEE, and the NASA Kepler and K2 missions, and obtain parallax and proper motion from {\it Gaia} DR2. We find that stellar samples from these surveys, even though they target different tracer populations and employ a variety of age estimation techniques, follow the same set of fundamental relations.

Paper PDF: 

veldisp_mw.pdf

Finding a planet that's truly like our own will need a holistic, multi-disciplinary approach to solve. Whilst there are multiple criteria for what constitutes a planet like ours, we can utilise large scale galactic archaeology surveys in exoplanetary science to refine the physical properties of planet-hosting stars, whilst uncovering their chemical makeup.

The paper will present extensive grids of non-LTE departure coefficients for ~13 different elements, the first paper of its kind. These grids were used for GALAH DR3. The results of the paper will however be based on a separate, line-by-line re-analysis of a subset of GALAH DR3 (~50000 stars), in LTE and in non-LTE. This will demonstrate the importance of taking departures from LTE into account in spectroscopic studies, when it comes to studying the mean Galactic chemical evolution and its dispersion.

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paper.pdf

Binary stellar systems form a large fraction of the Galaxy's stars. They are useful as laboratories to study the physical processes taking place within stars, and must be correctly taken into account when using observations of stars to study the structure and evolution of the Galaxy. The advent of large-scale spectroscopic and photometric surveys allows us to obtain large samples of binaries which permit characterisations of their populations.

Paper PDF: 

traven_galah_binaries_arxiv.pdf

The ensemble of chemical element abundance measurements for stars, along with precision distances and orbit properties, provides high-dimensional data to study the evolution of the Milky Way. With this third data release of the Galactic Archaeology with HERMES (GALAH) survey, we publish 678\,423 spectra for 588\,571 mostly nearby stars (81.2\% of stars are within $<$ 2 kpc), observed with the HERMES spectrograph at the Anglo-Australian Telescope.

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2011.02505.pdf

Using kinematics from Gaia and the large elemental abundance space of the second data release of the GALAH survey, we identify two new members of the Fimbulthul stellar stream, and chemically tag them to massive, multi-metallic globular cluster ω Centauri. Recent analysis of the second data release of Gaia had revealed the Fimbulthul stellar stream in the halo of the Milky Way. It had been proposed that the stream is associated with the ω Centauri, but this proposition relied exclusively upon the kinematics and metallicities of the stars to make the association. In this work, we find our two new members of the stream to be metal-poor stars that are enhanced in sodium and aluminium, typical of second population globular cluster stars, but not otherwise seen in field stars. Furthermore, the stars share the s-process abundance pattern seen in ω Centauri, which is rare in field stars. Apart from one star within 1.5 deg of ω Centauri, we find no other stars observed by GALAH spatially near ω Centauri or the Fimbulthul stream that could be kinematically and chemically linked to the cluster. Chemically tagging stars in the Fimbulthul stream to ω Centauri confirms the earlier work, and further links this tidal feature in the Milky Way halo to ω Centauri.

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1911.01548.pdf

The latest Gaia data release enables us to accurately identify stars that are more luminous than would be expected on the basis of their spectral type and distance. During an investigation of the 329 best Solar twin candidates uncovered among the spectra acquired by the GALAH survey, we identified 64 such over-luminous stars. In order to investigate their exact composition, we developed a data-driven methodology that can generate a synthetic photometric signature and spectrum of a single star.

Paper PDF: 

GALAH_triple_sun-like.pdf

One of the main goals of the Galah survey is to find stellar siblings in the Galactic disk and associate them to a common parent cluster by means of chemistry and dynamics. The success of such chemical tagging hinges critically on our ability to determine the abundances of late-type dwarf and giant stars with high precision, but also to assess whether their present-day abundance patterns truly reflect their original compositions.

Paper PDF: 

Gao_M67.pdf

We present a neural network autoencoder structure that is able to extract the most important latent spectral features from observed spectra and reconstruct a spectrum from those features. Because of the training process, the network is able to reproduce a spectrum of high signal to noise ratio that does not show any spectral peculiarities. Such generated spectra were used to identify various emission features among spectra acquired by multiple surveys using the HERMES spectrograph. Emission features were identified by a direct comparison of the observed and generated spectrum.

Paper PDF: 

galah_emission-line_stars.pdf