This represents our efforts to derive detailed abundances from LAMOST spectra using the cannon. We used GALAH as a source of training data, and we obtained access to the GALAH spectra in order to make chi^2 cuts on our training set different from those flagged in the GALAH dr2 catalog. A pdf of our latest draft (nearly ready for submission) is attached. Apologies for not circulating it sooner.

abstract: Large stellar surveys are revealing the chemodynamical structure of the Galaxy across a vast spatial extent.

Paper PDF: 

The_Milky_Way_s_enrichment_across_five_nucleosynthetic_channels_from_4_million_LAMOST_spectra.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

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.

Paper PDF: 

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

Gaia DR2 has revealed substructures in the phase space distribution of stars in the Milky Way. In particular, ridge like structures can be seen in the (R,V_phi) plane and asymmetric arches in (V_R, V_phi) plane. We show that the ridges are also clearly present when the (R,V_phi) plane is mapped by , ,, <|z|>,[Fe/H] and [alpha/Fe]. The last three maps suggest that stars along the ridges lie preferentially close to the Galactic midplane (|z|<0.2 kpc), and, have metallicity and alpha elemental abundance similar to that of the Sun.

Paper PDF: 

Linking_ridges__arches_and_vertical_waves_in_the_kinematics_of_the_Milky_Way.pdf

We use data from the second data releases of the ESA Gaia astrometric survey and the high-resolution GALAH spectroscopic survey to analyse the structure of our Galaxy's discs. With GALAH, we can separate the \alpha-rich and \alpha-poor discs (with respect to Fe), which are superposed in both position and velocity space, and examine their distributions in action space. We examine carefully the distribution of stars in the z-V_z phase plane in which a remarkable ``phase spiral'' was recently discovered.

Paper PDF: 

galah-survey-signatures.pdf

Sparse open clusters can be found at high galactic latitudes where loosely populated clusters are more easily detected against the lower stellar background. As bursty star formation takes place in the thin disk, the population of clusters far from the Galactic plane is hard to explain. We combined spectral parameters from the GALAH survey with the Gaia DR2 catalogue to study dynamics and chemistry of 5 old sparse high-latitude clusters in more detail.

Paper PDF: 

Nonexistence_of_clusters_Kos_2018.pdf

The Galactic Archaeology with HERMES (GALAH) survey is a large scale, magnitude limited, southern stellar spectroscopic survey providing spectra, stellar parameters and chemical abundances for stars located in different components of the Galaxy. Random selection, based only on object's brightness and its celestial coordinates, implies that a representative set of peculiar stellar types are observed.

Here we focus on carbon enhanced stars which can be identified by peculiar features present in their GALAH spectra.

Paper PDF: 

GALAH_carbon_enhanced_R2.pdf

Late-type stars deplete their atmospheric lithium abundance on the main sequence in a way that depends on mass, metallicity, age and possibly other parameters (rotation rate, activity. presence of binary companion or planets). There are still many unanswered questions about the evolution of this unique element in the Galaxy and in the stars themselves; it is unclear which parameters and physical mechanisms that govern Li depletion and if Galactic enrichment has proceeded differently in different stellar populations.

Paper PDF: 

MN_Letter_Lithium.pdf