Mapping the Milky Way with LAMOST– III. Complicated spatial structure in the outer disc

Wang, Hai-Feng; Liu, Chao; Xu, Yan; Wan, Jun-Chen; Deng, Licai

doi:10.1093/mnras/sty1058

Cited by 70 publications

(69 citation statements)

References 73 publications

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“…This model of thick disk formation predicts a negative radial age gradient in geometrically-defined thick disks, which was found to be indeed the case for the Milky Way using APOGEE data (Martig et al 2016). Flaring in Milky Way stellar populations of limited age range has been found by Kalberla et al (2014) Feast et al (2014) (Cepheids), Carraro et al (2015) (young clusters) and in LAMOST (Wan et al 2017;Wang et al 2018;Xiang et al 2018) and APOGEE (Mackereth et al 2017) mono-age populations. A proper Milky Way disk mass model is needed to asses the interplay among the flares of different mono-age populations on the overall scale-height variation with radius (that of the total disk mass).…”

Section: Variation Of Disk Thickness With Galactocentric Radiussupporting

confidence: 60%

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Yule-Simpson’s paradox in Galactic Archaeology

Minchev

Matijevič

Guiglion

et al. 2019

Monthly Notices of the Royal Astronomical Society

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Simpson's paradox, or Yule-Simpson effect, arises when a trend appears in different subsets of data but disappears or reverses when these subsets are combined. We describe here seven cases of this phenomenon for chemo-kinematical relations believed to constrain the Milky Way disk formation and evolution. We show that interpreting trends in relations, such as the radial and vertical chemical abundance gradients, the age-metallicity relation, and the metallicity-rotational velocity relation (MVR), can lead to conflicting conclusions about the Galaxy past if analyses marginalize over stellar age and/or birth radius. It is demonstrated that the MVR in RAVE giants is consistent with being always strongly negative, when narrow bins of [Mg/Fe] are considered. This is directly related to the negative radial metallicity gradients of stars grouped by common age (mono-age populations) due to the inside-out disk formation. The effect of the asymmetric drift can then give rise to a positive MVR trend in high-[α/Fe] stars, with a slope dependent on a given survey's selection function and observational uncertainties. We also study the variation of lithium abundance, A(Li), with [Fe/H] of AMBRE:HARPS dwarfs. A strong reversal in the positive A(Li)-[Fe/H] trend of the total sample is found for mono-age populations, flattening for younger groups of stars. Dissecting by birth radius shows strengthening in the positive A(Li)-[Fe/H] trend, shifting to higher [Fe/H] with decreasing birth radius; these observational results suggest new constraints on chemical evolution models. This work highlights the necessity for precise age estimates for large stellar samples covering wide spatial regions.

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Section: Variation Of Disk Thickness With Galactocentric Radiussupporting

confidence: 60%

“…Another example of a trend that can be linked to the Galaxy's past is disk flaring (e.g., Kazantzidis et al 2008;Bovy et al 2016;Kawata et al 2017;Wang et al 2018;Bland-Hawthorn & Gerhard 2016). Disk flaring can be related to the dynamical effect of merging satellites, e.g., the Sagittarius dwarf (Laporte et al 2018; Thomas et al 2019).…”

Section: Introductionmentioning

confidence: 99%

Yule-Simpson’s paradox in Galactic Archaeology

Minchev

Matijevič

Guiglion

et al. 2019

Monthly Notices of the Royal Astronomical Society

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“…Following an exponentialdecay profile, we estimate a scaleheight of z h = 0.634 ± 0.063 kpc, which is represented by the straight line in the figure. This is comparable with the z h = 0.637 0.056 −0.036 kpc result estimated by Wang et al (2018) for thick disc stars at R = 8 kpc in the LAMOST DR3 sample. However, our 97 per cent disc star sample is primarily comprised of thin disc stars, as seen in Fig.…”

Section: Dynamicssupporting

confidence: 88%

“…Mass transfer via a stellar wind can occur any time that the AGB star is losing mass via a sufficiently strong wind, and mass transfer via Roche lobe overflow can occur at any time during the AGB phase, regardless of whether the star is experiencing significant wind mass loss; see population synthesis studies of peculiar stars (e.g. Han et al 1995;Karakas, Tout & Lattanzio 2000;Abate et al 2013Abate et al , 2015Liu et al 2018).…”

Section: Comparison To Agb Yieldsmentioning

confidence: 99%

Discovery of s-process enhanced stars in the LAMOST survey

Norfolk

Casey

Karakas

et al. 2019

Monthly Notices of the Royal Astronomical Society

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Here we present the discovery of 895 s-process-rich candidates from 454 180 giant stars observed by the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) using a data-driven approach. This sample constitutes the largest number of s-process enhanced stars ever discovered. Our sample includes 187 s-process-rich candidates that are enhanced in both barium and strontium, 49 stars with significant barium enhancement only and 659 stars that show only a strontium enhancement. Most of the stars in our sample are in the range of effective temperature and log g typical of red giant branch (RGB) populations, which is consistent with our observational selection bias towards finding RGB stars. We estimate that only a small fraction (∼0.5 per cent) of binary configurations are favourable for s-process enriched stars. The majority of our s-process-rich candidates (95 per cent) show strong carbon enhancements, whereas only five candidates (<3 per cent) show evidence of sodium enhancement. Our kinematic analysis reveals that 97 per cent of our sample are disc stars, with the other 3 per cent showing velocities consistent with the Galactic halo. The scaleheight of the disc is estimated to be $z_{\rm h}=0.634 \pm {0.063}\, \mathrm{kpc}$, comparable with values in the literature. A comparison with yields from asymptotic giant branch (AGB) models suggests that the main neutron source responsible for the Ba and Sr enhancements is the 13C(α,n)16O reaction. We conclude that s-process-rich candidates may have received their overabundances via mass transfer from a previous AGB companion with an initial mass in the range $1\!-\!3\, \mathrm{M}_{\odot }$.

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“…Our Galaxy thus follows Briggs' rule for spiral galaxies 4 , which suggests that the origin of the warp is associated with torques forced by the massive inner disk 5 . The stellar disk traced by Cepheids follows the gas disk in terms of their amplitudes; the stellar disk extends to at least 20 kpc 6,7 . This morphology provides a crucial, updated map for studies of the kinematics and archaeology of the Galactic disk.…”

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confidence: 99%

An intuitive 3D map of the Galactic warp’s precession traced by classical Cepheids

et al. 2019

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The Milky Way's neutral hydrogen (HI) disk is warped and flared 1, 2 . However, a dearth of accurate HI-based distances has thus far prevented the development of an accurate Galactic disk model. Moreover, the extent to which our Galaxy's stellar and gas disk morphologies are mutually consistent is also unclear. Classical Cepheids, primary distance indicators with distance accuracies of 3-5% 3 , offer a unique opportunity to develop an intuitive and accurate three-dimensional picture. Here, we establish a robust Galactic disk model based on 1339 classical Cepheids. We provide strong evidence that the warp's line of nodes is not oriented in the Galactic Center-Sun direction. Instead, it subtends a mean angle of 17.5 • ± 1 • (formal) ±3 • (systematic) and exhibits a leading spiral pattern. Our Galaxy thus follows Briggs' rule for spiral galaxies 4 , which suggests that the origin of the warp is associated with torques forced by the massive inner disk 5 . The stellar disk traced by Cepheids follows the gas disk in terms of their amplitudes; the stellar disk extends to at least 20 kpc 6,7 . This morphology provides a crucial, updated map for studies of the kinematics and archaeology of the Galactic disk.We have compiled samples of classical Cepheids from the Wide-field Infrared Survey Explorer (WISE) catalogue of periodic variables 8 (our 'WISE Cepheid sample') as well as from a number of optical surveys (collectively referred to as our 'optical Cepheid sample'). We will discuss both samples separately, because the catalogues' optical and infrared passbands are characterised by significantly different photometric and extinction sensitivities. Highly accurate Cepheid distances can be estimated using their well-established wavelength-dependent period-luminosity relations. To mitigate the influence of extinction in the Galactic plane and of photometric uncertainties at infrared wavelengths, we adopted the 'infrared multi-passband optimal distance method' 9 to determine accurate Cepheid distances. Contaminants, including Type-II Cepheids, long-period eclipsing binaries and quasi-periodic variables were removed using Gaia Data Release 2 parallaxes 10 .Cepheids located in areas centered on the Magellanic Clouds were also excluded. Careful sample selection resulted in a tally of 2330 classical Cepheids for further analysis.Distances were converted to 3D XY z and spherical Rφz coordinates by adopting a reference frame centered on the Galactic Center and a solar Galactocentric distance R 0 = 8.0 kpc. Here, φ is the Galactocentric angle in the anticlockwise direction (aligned with the disk's rotation axis) with respect to the solar position (φ = 0 • ). Since Gaia parallaxes are reliable within ∼5 kpc, we only selected Cepheids within the volume R < 20, |z| < 2 kpc to avoid significant contamination by Type-II Cepheids. Our downselection included 1459 Cepheids with distances accurate to <5%, corresponding to a distance modulus standard deviation <0.108 mag. Cepheids located clearly away from the best-fitting warp model (∆ > 1 kp...

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Mapping the Milky Way with LAMOST– III. Complicated spatial structure in the outer disc

Cited by 70 publications

References 73 publications

Yule-Simpson’s paradox in Galactic Archaeology

Yule-Simpson’s paradox in Galactic Archaeology

Discovery of s-process enhanced stars in the LAMOST survey

An intuitive 3D map of the Galactic warp’s precession traced by classical Cepheids

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