The ESA Gaia astrometric mission and deep photometric surveys have revolutionized our knowledge of the Milky Way. There are many ongoing efforts to search these data for substructure to find evidence of individual accretion events that built up the Milky Way and its halo. One of these newly identified features, called Nyx, was announced as an accreted stellar stream traveling in the plane of the disk.

Paper PDF: 

Nix_on_Nyx.pdf

Due to its proximity the Orion star forming region is often used as a proxy to study processes related to star formation and observe young stars in the environment they were born in. Orion is getting additional attention within the Gaia DR2, as distance measurements are now good enough that a three dimensional structure of the complex can be explored.

Paper PDF: 

Orion_chemistry-5.pdf

Chemical tagging seeks to identify unique star formation sites from present-day stellar abundances. Previous techniques have treated each abundance dimension as being statistically independent, despite theoretical expectations that many elements can be produced by more than one nucleosynthetic process. In this work we introduce a data-driven model of nucleosynthesis where a set of latent factors (e.g., nucleosynthetic yields) contribute to all stars with different scores, and clustering (e.g., chemical tagging) is modelled by a mixture of multivariate gaussians in a lower-dimensiona

Paper PDF: 

mcfa.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

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.

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Gao_M67.pdf

We present a study using the second data release of the GALAH survey of stellar parameters and elemental abundances of 15 pairs of stars identified by Oh et al. They identified these pairs as potentially co-moving pairs using proper motions and parallaxes from Gaia DR1. We find that 11 very wide (>1 pc) pairs of stars do in fact have similar Galactic orbits, while a further four claimed co-moving pairs are not truly co-orbiting.

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sty3042.pdf

One of the main motivations for the GALAH survey is to measure abundances of many elements in sufficiently large number of stars that some of them can be identified as stars that were born in the same cluster but all indications of this fact have been lost, except for the chemical fingerprint. Chemical tagging can reveal the connection between such stars, but state of the art observations and analytical methods will be needed to actually perform this task.

Paper PDF: 

Chemtag_short.pdf

Almost all spiral galaxies have a second disk component, the thick disk, in addition to the thin disk which defines their disk structure. Thick disks are believed to be ancient structures that predates the formation of the thin disks, but how they fit in to the overall picture of galaxy formation remains unknown. Although our Galaxy has a thick disk, the properties of this ancient component are not yet well determined.

Paper PDF: 

thickdisk_paper_GALAH.pdf

The first generation of large-scale chemical tagging surveys, in particular the High Efficiency and Resolution Multi-Element Spectrograph (HERMES)/Galactic Archaeology with HERMES million star survey, promises to vastly expand our understanding of the chemical and dynamical evolution of the Galaxy. This, however, is contingent on our ability to confidently perform chemical tagging on such a large data set.

HERMES is a multi-fibre spectrograph being built for the AAT 3.9m telescope, designed to simultaneously obtain high resolution (R ˜ 28000) spectra for ˜ 400 stars over a 2° field of view. The Galactic Archaeology with HERMES (GALAH) Survey is a major Australian-led project to obtain detailed elemental abundances for a million stars, with the goal of using chemical tagging to decipher the formation history of the Milky Way.