The GALAH survey: the data reduction pipeline

Kos, Janez; Lin, Jane; Zwitter, T.; Zerjal, M.; Sharma, Sanjib; Bland-Hawthorn, Joss; Asplund, Martin; Casey, Andrew R.; Silva, Gayandhi M. De; Freeman, K. C.; Martell, Sarah L.; Simpson, Jeffrey D.; Schlesinger, Katharine J.; Zucker, D. B.; Anguiano, Borja; Bacigalupo, Carlos; Bedding, Timothy R.; Betters, Christopher H.; Costa, G. S. Da; Duong, Ly; Hyde, E. A.; Ireland, Michael; Kafle, Prajwal R.; Leon-Saval, Sergio G.; Lewis, Geraint F.; Munari, U.; Nataf, David M.; Stello, Dennis; Tinney, C. G.; Traven, G.; Watson, Fred; Wittenmyer, Robert A.

doi:10.1093/mnras/stw2064

Cited by 72 publications

(84 citation statements)

References 28 publications

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“…Additional data processing (barycentric correction, telluric correction, co-adding) were done with custom python scripts. We used the GUESS code, which is also used by the GALAH survey, to determine radial velocities and estimate initial stellar parameters (Kos et al 2017). The final stellar parameters were obtained with the spectral synthesis software Spectroscopy Made Easy (Valenti & Piskunov 1996;Piskunov & Valenti 2017) using 1D LTE marcs model atmospheres (Gustafsson et al 2008).…”

Section: Data Description and Analysismentioning

confidence: 99%

HERBS II: Detailed chemical compositions of Galactic bulge stars

Duong

Asplund

Nataf

et al. 2019

Monthly Notices of the Royal Astronomical Society

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This work explores the detailed chemistry of the Milky Way bulge using the HERMES spectrograph on the Anglo-Australian Telescope. Here we present the abundance ratios of 13 elements for 832 red giant branch and clump stars along the minor bulge axis at latitudes b = −10 • , −7.5 and −5 • . Our results show that none of the abundance ratios vary significantly with latitude. We also observe disk-like [Na/Fe] abundance ratios, which indicates the bulge does not contain helium-enhanced populations as observed in some globular clusters. Helium enhancement is therefore not the likely explanation for the double red-clump observed in the bulge. We confirm that bulge stars mostly follow abundance trends observed in the disk. However, this similarity is not confirmed across for all elements and metallicity regimes. The more metal-poor bulge population at [Fe/H] −0.8 is enhanced in the elements associated with core collapse supernovae (SNeII). In addition, the [La/Eu] abundance ratio suggests higher r-process contribution, and likely higher star formation in the bulge compared to the disk. This highlights the complex evolution in the bulge, which should be investigated further, both in terms of modelling; and with additional observations of the inner Galaxy.

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Section: Data Description and Analysismentioning

confidence: 99%

HERBS II: Detailed chemical compositions of Galactic bulge stars

Duong

Asplund

Nataf

et al. 2019

Monthly Notices of the Royal Astronomical Society

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“…The GALAH survey's observing procedures can be found in Martell et al (2017). In-depth descriptions of the spectral reduction, stellar parameter and abundance inference pipelines can be found in Kos et al (2016) and Buder et al (2018). Below we will briefly describe the details from those papers pertinent to this work.…”

Section: Datamentioning

confidence: 99%

“…HERMES simultaneously acquires spectra for ∼ 360 science targets using four independent cameras with non-contiguous wavelength coverage totalling ∼ 1000 Å at a spectral resolving power of R ≈ 28, 000. The spectra were reduced using an based pipeline that was developed specifically for GALAH and optimized for speed, accuracy, and consistency (Kos et al 2016).…”

Section: Datamentioning

confidence: 99%

The GALAH Survey: Chemically tagging the Fimbulthul stream to the globular cluster ω Centauri

Simpson

Martell

Costa

et al. 2019

Monthly Notices of the Royal Astronomical Society

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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 Cen, 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 Cen, which is rare in field stars. Apart from one star within 1.5 deg of ω Cen, we find no other stars observed by GALAH spatially near ω Cen or the Fimbulthul stream that could be kinematically and chemically linked to the cluster. Chemically tagging stars in the Fimbulthul stream to ω Cen confirms the earlier work, and further links this tidal feature in the Milky Way halo to ω Cen.

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“…We note that our data reduction process is independent of the GALAH reduction pipeline, most importantly we do not correct for the tilted PSF of HERMES spectra (Kos et al 2017), which may reduce the resolution and signal to noise towards the corners of each CCD. The spectral resolving power is lowered by up to ≈15%, and the SNR is lowered by up to ≈5% (Kos et al 2017). This affects all fibre bundles, but is minimised towards the CCD centre.…”

Section: Data Reductionmentioning

confidence: 99%

HERBS I: Metallicity and alpha enhancement along the Galactic bulge minor axis

Duong

Asplund

Nataf

et al. 2019

Monthly Notices of the Royal Astronomical Society

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To better understand the origin and evolution of the Milky Way bulge, we have conducted a survey of bulge red giant branch and clump stars using the HERMES spectrograph on the Anglo-Australian Telescope. We targeted ARGOS survey stars with pre-determined bulge memberships, covering the full metallicity distribution function. The spectra have signal-tonoise ratios comparable to, and were analysed using the same methods as the GALAH survey. In this work we present the survey design, stellar parameters, distribution of metallicity and alpha-element abundances along the minor bulge axis at latitudes b = −10 • , −7.5 • and −5 • . Our analysis of ARGOS stars indicates that the centroids of ARGOS metallicity components should be located ≈0.09 dex closer together. The vertical distribution of α-element abundances is consistent with the varying contributions of the different metallicity components. Closer to the plane, alpha abundance ratios are lower as the metal-rich population dominates. At higher latitudes, the alpha abundance ratios increase as the number of metal-poor stars increases. However, we find that the trend of alpha-enrichment with respect to metallicity is independent of latitude. Comparison of our results with those of GALAH DR2 revealed that for [Fe/H] ≈ −0.8, the bulge shares the same abundance trend as the high-α disk population. However, the metal-poor bulge population ([Fe/H] −0.8) show enhanced alpha abundance ratios compared to the disk/halo. These observations point to fairly rapid chemical evolution in the bulge, and that the metal-poor bulge population does not share the same similarity with the disk as the more metal-rich populations.

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The GALAH survey: the data reduction pipeline

Cited by 72 publications

References 28 publications

HERBS II: Detailed chemical compositions of Galactic bulge stars

HERBS II: Detailed chemical compositions of Galactic bulge stars

The GALAH Survey: Chemically tagging the Fimbulthul stream to the globular cluster ω Centauri

HERBS I: Metallicity and alpha enhancement along the Galactic bulge minor axis

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