The GALAH survey: scientific motivation

Silva, G.M. De; Freeman, K. C.; Bland-Hawthorn, Joss; Martell, Sarah L.; Boer, Elisabeth Wylie de; Asplund, Martin; Keller, Stefan; Sharma, Sanjib; Zucker, D. B.; Zwitter, T.; Anguiano, Borja; Bacigalupo, Carlos; Bayliss, Daniel; Beavis, M.A.; Bergemann, M.; Campbell, Simon; Cannon, R. D.; Carollo, D.; Casagrande, Luca; Casey, Andrew R.; Costa, G. S. Da; D’Orazi, V.; Dotter, Aaron; Duong, Ly; Heger, Alexander; Ireland, Michael; Kafle, Prajwal R.; Kos, Janez; Lattanzio, John C.; Lewis, Geraint F.; Lin, Jane; Lind, Karin; Munari, U.; Nataf, David M.; O'Toole, S. J.; Parker, Quentin A.; Reid, Warren A.; Schlesinger, Katharine J.; Sheinis, Andrew; Simpson, Jeffrey D.; Stello, Dennis; Ting, Yuan-Sen; Traven, G.; Watson, Fred; Wittenmyer, Robert A.; Yong, David; Žerjal, M.

doi:10.1093/mnras/stv327

Cited by 671 publications

(374 citation statements)

References 127 publications

(131 reference statements)

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“…This database is especially interesting when used in combination with the data from the Kepler/K2 mission, because this would allow us to investigate stellar populations also with photometry. The ongoing GALAH survey (De Silva et al 2015), a large Australian project that will measure the abundances of thirty elements together with HERMES providing spectrographic measurements of radial velocities is another example to which the Galaxy Model could be applied to investigate the galactic archaeology and archeochemistry. Finally, our model can be applied also to entirely different astrophysical scales, such as in asteroseismology.…”

Section: Discussionmentioning

confidence: 99%

Spiral arm kinematics for Milky Way stellar populations

Pasetto

Natale

Kawata

et al. 2016

Mon. Not. R. Astron. Soc.

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We present a new theoretical population synthesis model (the Galaxy Model) to examine and deal with large amounts of data from surveys of the Milky Way and to decipher the present and past structure and history of our own Galaxy.We assume the Galaxy to consist of a superposition of many composite stellar populations belonging to the thin and thick disks, the stellar halo and the bulge, and to be surrounded by a single dark matter halo component. A global model for the Milky Way's gravitational potential is built up self-consistently with the density profiles from the Poisson equation. In turn, these density profiles are used to generate synthetic probability distribution functions (PDFs) for the distribution of stars in colour-magnitude diagrams (CMDs). Finally, the gravitational potential is used to constrain the stellar kinematics by means of the moment method on a (perturbed)-distribution function. Spiral arms perturb the axisymmetric disk distribution functions in the linear response framework of density-wave theory where we present an analytical formula of the so-called 'reduction factor' using Hypergeometric functions.Finally, we consider an analytical non-axisymmetric model of extinction and an algorithm based on the concept of probability distribution function to handle colour magnitude diagrams with a large number of stars. A genetic algorithm is presented to investigate both the photometric and kinematic parameter space.This galaxy model represents the natural framework to reconstruct the structure of the Milky Way from the heterogeneous data set of surveys such as Gaia-ESO, SEGUE, APOGEE2, RAVE and the Gaia mission.

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Section: Discussionmentioning

confidence: 99%

Spiral arm kinematics for Milky Way stellar populations

Pasetto

Natale

Kawata

et al. 2016

Mon. Not. R. Astron. Soc.

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“…Examples of such surveys are the Gaia-ESO Public Spectroscopic Survey (Gilmore et al 2012;Randich et al 2013), RAVE (Steinmetz et al 2006), APOGEE (Allende Prieto et al 2008), and GALAH (De Silva et al 2015). To test that a method yields robust results, it should be applied to a set of spectra with known parameters to verify that the results agree.…”

Section: Introductionmentioning

confidence: 99%

GaiaFGK benchmark stars: Effective temperatures and surface gravities

Heiter

Jofré

Gustafsson

et al. 2015

A&A

287

414

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Context. In the era of large Galactic stellar surveys, carefully calibrating and validating the data sets has become an important and integral part of the data analysis. Moreover, new generations of stellar atmosphere models and spectral line formation computations need to be subjected to benchmark tests to assess any progress in predicting stellar properties. Aims. We focus on cool stars and aim at establishing a sample of 34 Gaia FGK benchmark stars with a range of different metallicities. The goal was to determine the effective temperature and the surface gravity independently of spectroscopy and atmospheric models as far as possible. Most of the selected stars have been subjected to frequent spectroscopic investigations in the past, and almost all of them have previously been used as reference, calibration, or test objects. Methods. Fundamental determinations of T eff and log g were obtained in a systematic way from a compilation of angular diameter measurements and bolometric fluxes and from a homogeneous mass determination based on stellar evolution models. The derived parameters were compared to recent spectroscopic and photometric determinations and to gravity estimates based on seismic data. Results. Most of the adopted diameter measurements have formal uncertainties around 1%, which translate into uncertainties in effective temperature of 0.5%. The measurements of bolometric flux seem to be accurate to 5% or better, which contributes about 1% or less to the uncertainties in effective temperature. The comparisons of parameter determinations with the literature in general show good agreements with a few exceptions, most notably for the coolest stars and for metal-poor stars. Conclusions. The sample consists of 29 FGK-type stars and 5 M giants. Among the FGK stars, 21 have reliable parameters suitable for testing, validation, or calibration purposes. For four stars, future adjustments of the fundamental T eff are required, and for five stars the log g determination needs to be improved. Future extensions of the sample of Gaia FGK benchmark stars are required to fill gaps in parameter space, and we include a list of suggested candidates.

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“…The targeted wavelength regions of the VLT/GIRAFFE spectrograph contain two strong Mg lines, 5528 Å and 8806 Å, detectable in all FGK type stars down to low metallicities. For stars in the solar neighbourhood, the GALAH survey (De Silva et al 2015) aims at a higher precision (∼0.05 dex) for many elements with the aim to identify dispersed star clusters (Zucker et al 2012). The wavelength settings of the AAT/HERMES instrument contain two weak Mg lines, 5711 Å and 7691 Å, suitable for analysis of high-metallicity stars.…”

Section: Introductionmentioning

confidence: 99%

Mg line formation in late-type stellar atmospheres

Osorio

Barklem

Lind

et al. 2015

A&A

Self Cite

130

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Context. Magnesium is an element of significant astrophysical importance, often traced in late-type stars using lines of neutral magnesium, which is expected to be subject to departures from local thermodynamic equilibrium (LTE). The importance of Mg, together with the unique range of spectral features in late-type stars probing different parts of the atom, as well as its relative simplicity from an atomic physics point of view, makes it a prime target and test bed for detailed ab initio non-LTE modelling in stellar atmospheres. Previous non-LTE modelling of spectral line formation has, however, been subject to uncertainties due to lack of accurate data for inelastic collisions with electrons and hydrogen atoms. Aims. In this paper we build and test a Mg model atom for spectral line formation in late-type stars with new or recent inelastic collision data and no associated free parameters. We aim to reduce these uncertainties and thereby improve the accuracy of Mg non-LTE modelling in late-type stars.Methods. For the low-lying states of Mg i, electron collision data were calculated using the R-matrix method. Hydrogen collision data, including charge transfer processes, were taken from recent calculations by some of us. Calculations for collisional broadening by neutral hydrogen were also performed where data were missing. These calculations, together with data from the literature, were used to build a model atom. This model was then employed in the context of standard non-LTE modelling in 1D (including average 3D) model atmospheres in a small set of stellar atmosphere models. First, the modelling was tested by comparisons with observed spectra of benchmark stars with well-known parameters. Second, the spectral line behaviour and uncertainties were explored by extensive experiments in which sets of collisional data were changed or removed. Results. The modelled spectra agree well with observed spectra from benchmark stars, showing much better agreement with line profile shapes than with LTE modelling. The line-to-line scatter in the derived abundances shows some improvements compared to LTE (where the cores of strong lines must often be ignored), particularly when coupled with averaged 3D models. The observed Mg emission features at 7 and 12 μm in the spectra of the Sun and Arcturus, which are sensitive to the collision data, are reasonably well reproduced. Charge transfer with H is generally important as a thermalising mechanism in dwarfs, but less so in giants. Excitation due to collisions with H is found to be quite important in both giants and dwarfs. The R-matrix calculations for electron collisions also lead to significant differences compared to when approximate formulas are employed. The modelling predicts non-LTE abundance corrections ΔA(Mg) NLTE−LTE in dwarfs, both solar metallicity and metal-poor, to be very small (of order 0.01 dex), even smaller than found in previous studies. In giants, corrections vary greatly between lines, but can be as large as 0.4 dex. Conclusions. Our results emphasise ...

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The GALAH survey: scientific motivation

Cited by 671 publications

References 127 publications

Spiral arm kinematics for Milky Way stellar populations

Spiral arm kinematics for Milky Way stellar populations

GaiaFGK benchmark stars: Effective temperatures and surface gravities

Mg line formation in late-type stellar atmospheres

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