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Lind, Karin
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Publications (10 of 44) Show all publications
Simpson, J. D., Martell, S. L., Da Costa, G., Casey, A. R., Freeman, K. C., Horner, J., . . . Nordlander, T. (2019). The GALAH survey: Co-orbiting stars and chemical tagging. Monthly notices of the Royal Astronomical Society, 482(4), 5302-5315
Open this publication in new window or tab >>The GALAH survey: Co-orbiting stars and chemical tagging
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2019 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 482, no 4, p. 5302-5315Article in journal (Refereed) Published
Abstract [en]

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. Eight of the 11 co-orbiting pairs have reliable stellar parameters and abundances, and we find that three of those are quite similar in their abundance patterns, while five have significant [Fe/H] differences. For the latter, this indicates that they could be co-orbiting because of the general dynamical coldness of the thin disc, or perhaps resonances induced by the Galaxy, rather than a shared formation site. Stars such as these, wide binaries, debris of past star formation episodes, and coincidental co-orbiters, are crucial for exploring the limits of chemical tagging in the Milky Way.

Keywords
Galaxy: disc, stars: abundances, stars: formation
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-368651 (URN)10.1093/mnras/sty3042 (DOI)
Available from: 2018-12-06 Created: 2018-12-06 Last updated: 2019-01-16Bibliographically approved
Karovicova, I., White, T. R., Nordlander, T., Lind, K., Casagrande, L., Ireland, M. J., . . . Asplund, M. (2018). Accurate effective temperatures of the metal-poor benchmark stars HD140283, HD122563, and HD103095 from CHARA interferometry. Monthly notices of the Royal Astronomical Society, 475(1), L81-L85
Open this publication in new window or tab >>Accurate effective temperatures of the metal-poor benchmark stars HD140283, HD122563, and HD103095 from CHARA interferometry
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2018 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 475, no 1, p. L81-L85Article in journal (Refereed) Published
Abstract [en]

Large stellar surveys of the MilkyWay require validation with reference to a set of 'benchmark' stars whose fundamental properties are well determined. For metal-poor benchmark stars, disagreement between spectroscopic and interferometric effective temperatures has called the reliability of the temperature scale into question. We present new interferometric measurements of three metal-poor benchmark stars, HD140283, HD122563, and HD103095, from which we determine their effective temperatures. The angular sizes of all the stars were determined from observations with the PAVO beam combiner at visible wavelengths at the CHARA array, with additional observations of HD103095 made with the VEGA instrument, also at the CHARA array. Together with photometrically derived bolometric fluxes, the angular diameters give a direct measurement of the effective temperature. For HD140283, we find theta(LD) = 0.324 +/- 0.005 mas, T-eff = 5787 +/- 48 K; for HD122563,theta(LD) = 0.926 +/- 0.011 mas, T-eff = 4636 +/- 37 K; and for HD103095,theta(LD) = 0.595 +/- 0.007 mas, T-eff = 5140 +/- 49 K. Our temperatures for HD140283 and HD103095 are hotter than the previous interferometric measurements by 253 and 322 K, respectively. We find good agreement between our temperatures and recent spectroscopic and photometric estimates. We conclude some previous interferometric measurements have been affected by systematic uncertainties larger than their quoted errors.

Place, publisher, year, edition, pages
OXFORD UNIV PRESS, 2018
Keywords
standards, techniques: interferometric, surveys, stars: individual: HD103095, stars: individual: HD122563, stars: individual: HD140283
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-360553 (URN)10.1093/mnrasl/sly010 (DOI)000438222600018 ()
Funder
Australian Research Council, DP150100250Australian Research Council, FT160100402Australian Research Council, DE140101364EU, European Research Council, 320360Swedish Research Council, 2015 - 004153Swedish National Space Board
Available from: 2018-09-20 Created: 2018-09-20 Last updated: 2018-09-20Bibliographically approved
Amarsi, A. M., Nordlander, T., Barklem, P., Asplund, M., Collet, R. & Lind, K. (2018). Effective temperature determinations of late-type stars based on 3D non-LTE Balmer line formation. Astronomy and Astrophysics, 615, Article ID A139.
Open this publication in new window or tab >>Effective temperature determinations of late-type stars based on 3D non-LTE Balmer line formation
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2018 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 615, article id A139Article in journal (Refereed) Published
Abstract [en]

Hydrogen Balmer lines are commonly used as spectroscopic effective temperature diagnostics of late-type stars. However, reliable inferences require accurate model spectra, and the absolute accuracy of classical methods that are based on one-dimensional (1D) hydrostatic model atmospheres and local thermodynamic equilibrium (LTE) is still unclear. To investigate this, we carry out 3D non-LTE calculations for the Balmer lines, performed, for the first time, over an extensive grid of 3D hydrodynamic STAGGER model atmospheres. For H alpha, H beta, and H gamma we find significant 1D non-LTE versus 3D non-LTE differences (3D effects): the outer wings tend to be stronger in 3D models, particularly for H gamma, while the inner wings can be weaker in 3D models, particularly for H alpha. For H alpha, we also find significant 3D LTE versus 3D non-LTE differences (non-LTE effects): in warmer stars (T-eff approximate to 6500 K) the inner wings tend to be weaker in non-LTE models, while at lower effective temperatures (T-eff approximate to 4500 K) the inner wings can be stronger in non-LTE models; the non-LTE effects are more severe at lower metallicities. We test our 3D non-LTE models against observations of well-studied benchmark stars. For the Sun, we infer concordant effective temperatures from H alpha, H beta, and H gamma; however the value is too low by around 50 K which could signal residual modelling shortcomings. For other benchmark stars, our 3D non-LTE models generally reproduce the effective temperatures to within 1 sigma uncertainties. For H alpha, the absolute 3D effects and non-LTE effects can separately reach around 100 K, in terms of inferred effective temperatures. For metal-poor turn-off stars, 1D LTE models of H alpha can underestimate effective temperatures by around 150 K. Our 3D non-LTE model spectra are publicly available, and can be used for more reliable spectroscopic effective temperature determinations.

Keywords
radiative transfer, line: formation, line: profiles, stars: atmospheres, stars: late-type
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-361994 (URN)10.1051/0004-6361/201732546 (DOI)000440220000006 ()
Funder
Swedish Research Council, 2015004153Australian Research Council, DP150100250Swedish Research CouncilKnut and Alice Wallenberg Foundation
Available from: 2018-10-03 Created: 2018-10-03 Last updated: 2018-10-03Bibliographically approved
Bensby, T. & Lind, K. (2018). Exploring the production and depletion of lithium in the Milky Way stellar disk. Astronomy and Astrophysics, 615, Article ID A151.
Open this publication in new window or tab >>Exploring the production and depletion of lithium in the Milky Way stellar disk
2018 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 615, article id A151Article in journal (Refereed) Published
Abstract [en]

Despite the recent availability of large samples of stars with high-precision Li abundances, there are 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 govern Li depletion in late-type stars and if Galactic enrichment has proceeded differently in different stellar populations. With this study we aim to explore these questions further by mapping the evolution of Li with stellar mass, age, and effective temperature for Milky Way disk stars, linking the metal-poor and metal-rich regimes, and how Li differs in the thin and thick disks. We determine Li abundances for a well-studied sample of 714 F and G dwarf, turn-off, and subgiant stars in the solar neighbourhood. The analysis is based on line synthesis of the Li-7 line at 6707 angstrom in high-resolution and high-signal-to-noise ratio echelle spectra, obtained with the MIKE, FEROS, SOFIN, UVES, and FIES spectrographs. The presented Li abundances are corrected for non-LTE effects. Out of the sample of 714 stars, we are able to determine Li abundances for 394 stars and upper limits on the Li abundance for another 121 stars. Out of 36 stars that are listed as exoplanet host stars, 18 have well-determined Li abundances and 6 have Li upper limits. Our main finding is that there are no signatures of Li production in stars associated with the thick disk. Instead the Li abundance trend is decreasing with metallicity for these thick disk stars. Significant Li production is however seen in the thin disk, with a steady increase towards super-solar metallicities. At the highest metallicities, however, around [Fe/H] approximate to +0.3, we tentatively confirm the recent discovery that the Li abundances level out. Our finding contradicts the other recent studies that found that Li is also produced in the thick disk. We find that this is likely due to the alpha-enhancement criteria which those studies used to define their thick disk samples. By using the more robust age criteria, we are able to define a thick disk stellar sample that is much less contaminated by thin disk stars. Furthermore, we also tentatively confirm the age-Li correlation for solar twin stars, and we find that there is no correlation between Li abundance and whether the stars have detected exoplanets or not. The major conclusion that can be drawn from this study is that no significant Li production relative to the primordial abundance took place during the first few billion years of the Milky Way, an era coinciding with the formation and evolution of the thick disk. Significant Li enrichment then took place once long-lived low-mass stars (acting on a timescale longer than SNIa) had had time to contribute to the chemical enrichment of the interstellar medium.

Place, publisher, year, edition, pages
EDP Sciences, 2018
Keywords
Galaxy: disk, Galaxy: formation, Galaxy: evolution, stars: abundances, stars: fundamental parameters
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-362032 (URN)10.1051/0004-6361/201833118 (DOI)000440419600001 ()
Funder
Knut and Alice Wallenberg FoundationSwedish Research Council, 2015-00415_3
Available from: 2018-10-16 Created: 2018-10-16 Last updated: 2018-10-29Bibliographically approved
Hayden, M. R., Recio-Blanco, A., de Laverny, P., Mikolaitis, S., Guiglion, G., Hill, V., . . . Zwitter, T. (2018). The Gaia-ESO Survey: Churning through the Milky Way. Astronomy and Astrophysics, 609, Article ID A79.
Open this publication in new window or tab >>The Gaia-ESO Survey: Churning through the Milky Way
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2018 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 609, article id A79Article in journal (Refereed) Published
Abstract [en]

Context: There have been conflicting results with respect to the extent that radial migration has played in the evolution of the Galaxy. Additionally, observations of the solar neighborhood have shown evidence of a merger in the past history of the Milky Way that drives enhanced radial migration.

Aims: We attempt to determine the relative fraction of stars that have undergone significant radial migration by studying the orbital properties of metal-rich ([Fe/H] > 0.1) stars within 2 kpc of the Sun. We also aim to investigate the kinematic properties, such as velocity dispersion and orbital parameters, of stellar populations near the Sun as a function of [Mg/Fe] and [Fe/H], which could show evidence of a major merger in the past history of the Milky Way.

Methods: We used a sample of more than 3000 stars selected from the fourth internal data release of the Gaia-ESO Survey. We used the stellar parameters from the Gaia-ESO Survey along with proper motions from PPMXL to determine distances, kinematics, and orbital properties for these stars to analyze the chemodynamic properties of stellar populations near the Sun.

Results: Analyzing the kinematics of the most metal-rich stars ([Fe/H] > 0 : 1), we find that more than half have small eccentricities (e < 0 : 2) or are on nearly circular orbits. Slightly more than 20% of the metal-rich stars have perigalacticons R-p > 7 kpc. We find that the highest [Mg/ Fe], metal-poor populations have lower vertical and radial velocity dispersions compared to lower [Mg/Fe] populations of similar metallicity by similar to 10 km s(-1). The median eccentricity increases linearly with [Mg/Fe] across all metallicities, while the perigalacticon decreases with increasing [Mg/Fe] for all metallicities. Finally, the most [Mg/Fe]-rich stars are found to have significant asymmetric drift and rotate more than 40 km s(-1) slower than stars with lower [Mg/Fe] ratios.

Conclusions: While our results cannot constrain how far stars have migrated, we propose that migration processes are likely to have played an important role in the evolution of the Milky Way, with metal-rich stars migrating from the inner disk toward to solar neighborhood and past mergers potentially driving enhanced migration of older stellar populations in the disk.

Place, publisher, year, edition, pages
EDP SCIENCES S A, 2018
Keywords
Galaxy: kinematics and dynamics, Galaxy: disk, Galaxy: stellar content, Galaxy: structure
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-341569 (URN)10.1051/0004-6361/201730412 (DOI)000419996500001 ()
Funder
Knut and Alice Wallenberg FoundationEU, FP7, Seventh Framework Programme, 320360
Available from: 2018-02-12 Created: 2018-02-12 Last updated: 2018-02-12Bibliographically approved
Smiljanic, R., Franciosini, E., Bragaglia, A., Tautvaisiene, G., Fu, X., Pancino, E., . . . Zaggia, S. (2018). The Gaia-ESO Survey: properties of newly discovered Li-rich giants. Astronomy and Astrophysics, 617, Article ID A4.
Open this publication in new window or tab >>The Gaia-ESO Survey: properties of newly discovered Li-rich giants
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2018 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 617, article id A4Article in journal (Refereed) Published
Abstract [en]

Aims. We report 20 new lithium-rich giants discovered within the Gaia-ESO Survey, including the first Li-rich giant with an evolutionary stage confirmed by CoRoT (Convection, Rotation and planetary Transits) data. We present a detailed overview of the properties of these 20 stars. Methods. Atmospheric parameters and abundances were derived in model atmosphere analyses using medium-resolution GIRAFFE or high-resolution UVES (Ultraviolet and Visual Echelle Spectrograph) spectra. These results are part of the fifth internal data release of the Gaia-ESO Survey. The Li abundances were corrected for non-local thermodynamical equilibrium effects. Other stellar properties were investigated for additional peculiarities (the core of strong lines for signs of magnetic activity, infrared magnitudes, rotational velocities, chemical abundances, and Galactic velocities). We used Gaia DR2 parallaxes to estimate distances and luminosities. Results. The giants have A(Li) > 2.2 dex. The majority of them (14 of 20 stars) are in the CoRoT fields. Four giants are located in the field of three open clusters, but are not members. Two giants were observed in fields towards the Galactic bulge, but likely lie in the inner disc. One of the bulge field giants is super Li-rich with A(Li) = 4.0 dex. Conclusions. We identified one giant with infrared excess at 22 mu m. Two other giants, with large v sin i, might be Li-rich because of planet engulfment. Another giant is found to be barium enhanced and thus could have accreted material from a former asymptotic giant branch companion. Otherwise, in addition to the Li enrichment, the evolutionary stages are the only other connection between these new Li-rich giants. The CoRoT data confirm that one Li-rich giant is at the core-He burning stage. The other giants are concentrated in close proximity to the red giant branch luminosity bump, the core-He burning stages, or the early-asymptotic giant branch. This is very clear from the Gaia-based luminosities of the Li-rich giants. This is also seen when the CoRoT Li-rich giants are compared to a larger sample of 2252 giants observed in the CoRoT fields by the Gaia-ESO Survey, which are distributed throughout the red giant branch in the T-eff-log g diagram. These observations show that the evolutionary stage is a major factor for the Li enrichment in giants. Other processes, such as planet accretion, contribute at a smaller scale.

Keywords
stars: abundances, stars: evolution, stars: late-type
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-368643 (URN)10.1051/0004-6361/201833027 (DOI)000444606800001 ()
Available from: 2018-12-06 Created: 2018-12-06 Last updated: 2018-12-06Bibliographically approved
Zwitter, T., Kos, J., Chiavassa, A., Buder, S., Traven, G., Cotar, K., . . . Zerjal, M. (2018). The GALAH survey: accurate radial velocities and library of observed stellar template spectra. Monthly notices of the Royal Astronomical Society, 481(1), 645-654
Open this publication in new window or tab >>The GALAH survey: accurate radial velocities and library of observed stellar template spectra
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2018 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 481, no 1, p. 645-654Article in journal (Refereed) Published
Abstract [en]

GALAH is a large-scale magnitude-limited southern stellar spectroscopic survey. Its second data release (GALAH DR2) provides values of stellar parameters and abundances of 23 elements for 342 682 stars (Buder et al.). Here we add a description of the public release of radial velocities with a typical accuracy of 0.1 km s(-1) for 336 215 of these stars, achievable due to the large wavelength coverage, high resolving power, and good signal-to-noise ratio of the observed spectra, but also because convective motions in stellar atmosphere and gravitational redshift from the star to the observer are taken into account. In the process we derive medians of observed spectra that are nearly noiseless, as they are obtained from between 100 and 1116 observed spectra belonging to the same bin with a width of 50 K in temperature, 0.2 dex in gravity, and 0.1 dex in metallicity. Publicly released 1181 median spectra have a resolving power of 28 000 and trace the well-populated stellar types with metallicities between -0.6 and +0.3. Note that radial velocities from GALAH are an excellent match to the accuracy of velocity components along the sky plane derived by Gaia for the same stars. The level of accuracy achieved here is adequate for studies of dynamics within stellar clusters, associations, and streams in the Galaxy. So it may be relevant for studies of the distribution of dark matter.

Keywords
methods: data analysis, methods: observational, surveys, stars: fundamental parameters
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-368648 (URN)10.1093/mnras/sty2293 (DOI)000449651400048 ()
Available from: 2018-12-06 Created: 2018-12-06 Last updated: 2018-12-06
Kos, J., de Silva, G., Buder, S., Bland-Hawthorn, J., Sharma, S., Asplund, M., . . . Traven, G. (2018). The GALAH survey and Gaia DR2: (non-)existence of five sparse high-latitude open clusters. Monthly notices of the Royal Astronomical Society, 480(4), 5242-5259
Open this publication in new window or tab >>The GALAH survey and Gaia DR2: (non-)existence of five sparse high-latitude open clusters
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2018 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 480, no 4, p. 5242-5259Article in journal (Refereed) Published
Abstract [en]

Sparse open clusters can be found at high galactic latitudes where loosely populated clusters are more easily detected against the lower stellar background. Because most star formation takes place in the thin disc, the observed 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 the dynamics and chemistry of five old sparse high-latitude clusters in more detail. We find that four of them (NGC 1252, NGC 6994, NGC 7772, NGC 7826) - originally classified in 1888 - are not clusters but are instead chance projections on the sky. Member stars quoted in the literature for these four clusters are unrelated in our multidimensional physical parameter space; the quoted cluster properties in the literature are therefore meaningless. We confirm the existence of visually similar NGC 1901 for which we provide a probabilistic membership analysis. An overdensity in three spatial dimensions proves to be enough to reliably detect sparse clusters, but the whole six-dimensional space must be used to identify members with high confidence, as demonstrated in the case of NGC 1901.

Keywords
techniques: radial velocities, catalogues, surveys, parallaxes, proper motions
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-368649 (URN)10.1093/mnras/sty2171 (DOI)000449617100076 ()
Available from: 2018-12-06 Created: 2018-12-06 Last updated: 2018-12-06
Kos, J., Bland-Hawthor, J., Freeman, K., Buder, S., Traven, G., De Silva, G. M., . . . Wyse, R. (2018). The GALAH survey: chemical tagging of star clusters and new members in the Pleiades. Monthly notices of the Royal Astronomical Society, 473(4), 4612-4633
Open this publication in new window or tab >>The GALAH survey: chemical tagging of star clusters and new members in the Pleiades
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2018 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 473, no 4, p. 4612-4633Article in journal (Refereed) Published
Abstract [en]

The technique of chemical tagging uses the elemental abundances of stellar atmospheres to 'reconstruct' chemically homogeneous star clusters that have long since dispersed. The GALAH spectroscopic survey - which aims to observe one million stars using the Anglo-Australian Telescope - allows us to measure up to 30 elements or dimensions in the stellar chemical abundance space, many of which are not independent. How to find clustering reliably in a noisy high-dimensional space is a difficult problem that remains largely unsolved. Here, we explore t-distributed stochastic neighbour embedding (t-SNE) - which identifies an optimal mapping of a high-dimensional space into fewer dimensions - whilst conserving the original clustering information. Typically, the projection is made to a 2D space to aid recognition of clusters by eye. We show that this method is a reliable tool for chemical tagging because it can: (i) resolve clustering in chemical space alone, (ii) recover known open and globular clusters with high efficiency and low contamination, and (iii) relate field stars to known clusters. t-SNE also provides a useful visualization of a high-dimensional space. We demonstrate the method on a data set of 13 abundances measured in the spectra of 187 000 stars by the GALAH survey. We recover seven of the nine observed clusters (six globular and three open clusters) in chemical space with minimal contamination from field stars and low numbers of outliers. With chemical tagging, we also identify two Pleiades supercluster members (which we confirm kinematically), one as far as 6 degrees-one tidal radius away from the cluster centre.

Place, publisher, year, edition, pages
Oxford University Press, 2018
Keywords
methods: data analysis, stars: abundances, open clusters and associations: general, open clusters and associations: individual: Pleiades
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-346887 (URN)10.1093/mnras/stx2637 (DOI)000424117300024 ()
Funder
Australian Research Council, DE140100598, FT110100793, DP150104667
Available from: 2018-03-28 Created: 2018-03-28 Last updated: 2018-03-28Bibliographically approved
Duong, L., Freeman, K. C., Asplund, M., Casagrande, L., Buder, S., Lind, K., . . . Wyse, R. F. (2018). The GALAH survey: properties of the Galactic disc(s) in the solar neighbourhood. Monthly notices of the Royal Astronomical Society, 476(4), 5216-5232
Open this publication in new window or tab >>The GALAH survey: properties of the Galactic disc(s) in the solar neighbourhood
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2018 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 476, no 4, p. 5216-5232Article in journal (Refereed) Published
Abstract [en]

Using data from the GALAH pilot survey, we determine properties of the Galactic thin and thick discs near the solar neighbourhood. The data cover a small range of Galactocentric radius (7.9 less than or similar to R-GC less than or similar to 9.5 kpc), but extend up to 4 kpc in height from the Galactic plane, and several kpc in the direction of Galactic anti-rotation (at longitude 260 degrees <= l <= 280 degrees). This allows us to reliably measure the vertical density and abundance profiles of the chemically and kinematically defined 'thick' and 'thin' discs of the Galaxy. The thin disc (low-alpha population) exhibits a steep negative vertical metallicity gradient, at d[M/H]/dz = -0.18 +/- 0.01 dex kpc(-1), which is broadly consistent with previous studies. In contrast, its vertical alpha-abundance profile is almost flat, with a gradient of d[alpha/M]/dz = 0.008 +/- 0.002 dex kpc(-1). The steep vertical metallicity gradient of the low-a population is in agreement with models where radial migration has a major role in the evolution of the thin disc. The thick disc (high-alpha population) has a weaker vertical metallicity gradient d[M/H]/dz = -0.058 +/- 0.003 dex kpc(-1). The aabundance of the thick disc is nearly constant with height, d[alpha/M]/dz = 0.007 +/- 0.002 dex kpc(-1). The negative gradient in metallicity and the small gradient in [alpha/M] indicate that the high-alpha population experienced a settling phase, but also formed prior to the onset of major Type I alpha supernova enrichment. We explore the implications of the distinct alpha-enrichments and narrow [alpha/M] range of the sub-populations in the context of thick disc formation.

Place, publisher, year, edition, pages
OXFORD UNIV PRESS, 2018
Keywords
surveys, stars: abundances, Galaxy: disc, Galaxy: evolution, Galaxy: formation
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-357390 (URN)10.1093/mnras/sty525 (DOI)000432659800061 ()
Funder
Australian Research Council, DP150100250Australian Research Council, FT160100402
Available from: 2018-08-17 Created: 2018-08-17 Last updated: 2018-08-17Bibliographically approved
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