Random Forest identification of the thin disc, thick disc, and halo Gaia-DR2 white dwarf population

ABSTRACT The Transiting Exoplanet Survey Satellite (TESS) has already begun to discover what will ultimately be thousands of exoplanets around nearby cool bright stars. These potential host stars must be well understood to accurately characterize exoplanets at the individual and population levels. We present a catalogue of the chemo-kinematic properties of 2218 434 stars in the TESS Candidate Target List using survey data from Gaia DR2, APOGEE, GALAH, RAVE, LAMOST, and photometrically derived stellar properties from SkyMapper. We compute kinematic thin disc, thick disc, and halo membership probabilities for these stars and find that though the majority of TESS targets are in the thin disc, 4 per cent of them reside in the thick disc and <1 per cent of them are in the halo. The TESS Objects of Interest in our sample also display similar contributions from the thin disc, thick disc, and halo with a majority of them being in the thin disc. We also explore metallicity and [α/Fe] distributions for each Galactic component and show that each cross-matched survey exhibits metallicity and [α/Fe] distribution functions that peak from higher to lower metallicity and lower to higher [α/Fe] from the thin disc to the halo. This catalogue will be useful to explore planet occurrence rates, among other things, with respect to kinematics, component membership, metallicity, or [α/Fe].

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Co-formation of the thin and thick discs revealed by APOGEE-DR16 and Gaia-DR2

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3966 ◽

2020 ◽

Author(s):

Leandro Beraldo e Silva ◽

Victor P Debattista ◽

David Nidever ◽

João A S Amarante ◽

Bethany Garver

Keyword(s):

Solar Neighbourhood ◽

Full Sample ◽

Thick Disc ◽

Thin Disc ◽

Vertical Scale ◽

Stellar Halo ◽

Sph Simulation ◽

Gaia Dr2 ◽

Cross Match ◽

Age Estimates

Abstract Since thin disc stars are younger than thick disc stars on average, the thin disc is predicted by some models to start forming after the thick disc had formed, around 10 Gyr ago. Accordingly, no significant old thin disc population should exist. Using 6-D coordinates from Gaia-DR2 and age estimates from Sanders & Das (2018), we select ∼24000 old stars (${\tau > 10{\, \rm{Gyr}}}$, with uncertainties $\lesssim 15\%$) within $2{\, \rm{kpc}}$ from the Sun (full sample). A cross-match with APOGEE-DR16 (∼1000 stars) reveals comparable fractions of old chemically defined thin/thick disc stars. We show that the full sample pericenter radius (rper) distribution has three peaks, one associated with the stellar halo and the other two having contributions from the thin/thick discs. Using a high-resolution N-body+SPH simulation, we demonstrate that one peak, at ${r_\rm{per}}\approx 7.1{\, \rm{kpc}}$, is produced by stars from both discs which were born in the inner Galaxy and migrated to the Solar Neighbourhood. In the Solar Neighbourhood, ∼1/2 (∼1/3) of the old thin (thick) disc stars are classified as migrators. Our results suggest that thin/thick discs are affected differently by radial migration inasmuch as they have different eccentricity distributions, regardless of vertical scale heights. We interpret the existence of a significant old thin disc population as evidence for an early co-formation of thin/thick discs, arguing that clump instabilities in the early disc offer a compelling explanation for the observed trends.

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The AMBRE Project: r-process elements in the Milky Way thin and thick discs

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833782 ◽

2018 ◽

Vol 619 ◽

pp. A143 ◽

Cited By ~ 11

Author(s):

G. Guiglion ◽

P. de Laverny ◽

A. Recio-Blanco ◽

N. Prantzos

Keyword(s):

Chemical Evolution ◽

Milky Way ◽

Element Abundances ◽

Thick Disc ◽

Thin Disc ◽

Solar Metallicity ◽

R Process ◽

Process Elements ◽

Process Element ◽

The Eu

Context. The chemical evolution of neutron capture elements in the Milky Way disc is still a matter of debate. There is a lack of statistically significant catalogues of such element abundances, especially those of the r-process. Aims. We aim to understand the chemical evolution of r-process elements in Milky Way disc. We focus on three pure r-process elements Eu, Gd, and Dy. We also consider a pure s-process element, Ba, in order to disentangle the different nucleosynthesis processes. Methods. We take advantage of high-resolution FEROS, HARPS, and UVES spectra from the ESO archive in order to perform a homogeneous analysis on 6500 FGK Milky Way stars. The chemical analysis is performed thanks to the automatic optimization pipeline GAUGUIN. We present abundances of Ba (5057 stars), Eu (6268 stars), Gd (5431 stars), and Dy (5479 stars). Based on the [α/Fe] ratio determined previously by the AMBRE Project, we chemically characterize the thin and the thick discs, and a metal-rich α-rich population. Results. First, we find that the [Eu/Fe] ratio follows a continuous sequence from the thin disc to the thick disc as a function of the metallicity. Second, in thick disc stars, the [Eu/Ba] ratio is found to be constant, while the [Gd/Ba] and [Dy/Ba] ratios decrease as a function of the metallicity. These observations clearly indicate a different nucleosynthesis history in the thick disc between Eu and Gd–Dy. The [r/Fe] ratio in the thin disc is roughly around +0.1 dex at solar metallicity, which is not the case for Ba. We also find that the α-rich metal-rich stars are also enriched in r-process elements (like thick disc stars), but their [Ba/Fe] is very different from thick disc stars. Finally, we find that the [r/α] ratio tends to decrease with metallicity, indicating that supernovae of different properties probably contribute differently to the synthesis of r-process elements and α-elements. Conclusions. We provide average abundance trends for [Ba/Fe] and [Eu/Fe] with rather small dispersions, and for the first time for [Gd/Fe] and [Dy/Fe]. This data may help to constrain chemical evolution models of Milky Way r- and s-process elements and the yields of massive stars. We emphasize that including yields of neutron-star or black hole mergers is now crucial if we want to quantitatively compare observations to Galactic chemical evolution models.

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Testing the white dwarf mass-radius relation and comparing optical and far-UV spectroscopic results with Gaia DR2, HST and FUSE

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/sty1425 ◽

2018 ◽

Cited By ~ 4

Author(s):

S R G Joyce ◽

M A Barstow ◽

S L Casewell ◽

M R Burleigh ◽

J B Holberg ◽

...

Keyword(s):

White Dwarf ◽

Gaia Dr2

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The local rotation curve of the Milky Way based on SEGUE and RAVE data

Astronomy and Astrophysics ◽

10.1051/0004-6361/201731143 ◽

2018 ◽

Vol 614 ◽

pp. A63 ◽

Cited By ~ 8

Author(s):

K. Sysoliatina ◽

A. Just ◽

O. Golubov ◽

Q. A. Parker ◽

E. K. Grebel ◽

...

Keyword(s):

Rotation Curve ◽

Milky Way ◽

Tangential Velocity ◽

Solar Radius ◽

Tangential Component ◽

Peculiar Velocity ◽

Thick Disc ◽

Thin Disc ◽

Peculiar Motion ◽

Scale Length

Aims. We construct the rotation curve of the Milky Way in the extended solar neighbourhood using a sample of Sloan Extension for Galactic Understanding and Exploration (SEGUE) G-dwarfs. We investigate the rotation curve shape for the presence of any peculiarities just outside the solar radius as has been reported by some authors. Methods. Using the modified Strömberg relation and the most recent data from the RAdial Velocity Experiment (RAVE), we determine the solar peculiar velocity and the radial scale lengths for the three populations of different metallicities representing the Galactic thin disc. Subsequently, with the same binning in metallicity for the SEGUE G-dwarfs, we construct the rotation curve for a range of Galactocentric distances from 7 to 10 kpc. We approach this problem in a framework of classical Jeans analysis and derive the circular velocity by correcting the mean tangential velocity for the asymmetric drift in each distance bin. With SEGUE data we also calculate the radial scale length of the thick disc taking as known the derived peculiar motion of the Sun and the slope of the rotation curve. Results. The tangential component of the solar peculiar velocity is found to be V ⊙ = 4.47 ± 0.8 km s−1 and the corresponding scale lengths from the RAVE data are Rd(0 < [Fe/H] < 0.2) = 2.07 ± 0.2 kpc, Rd(−0.2 < [Fe/H] < 0) = 2.28 ± 0.26 kpc and Rd(−0.5 < [Fe/H] <−0.2) = 3.05 ± 0.43 kpc. In terms of the asymmetric drift, the thin disc SEGUE stars are demonstrated to have dynamics similar to the thin disc RAVE stars, therefore the scale lengths calculated from the SEGUE sample have close values: Rd(0 < [Fe/H] < 0.2) = 1.91 ± 0.23 kpc, Rd(−0.2 < [Fe/H] < 0) = 2.51 ± 0.25 kpc and Rd(−0.5 < [Fe/H] <−0.2) = 3.55 ± 0.42 kpc. The rotation curve constructed through SEGUE G-dwarfs appears to be smooth in the selected radial range 7 kpc < R < 10 kpc. The inferred power law index of the rotation curve is 0.033 ± 0.034, which corresponds to a local slope of dV c∕dR = 0.98 ± 1 km s−1 kpc−1. The radial scale length of the thick disc is 2.05 kpc with no essential dependence on metallicity. Conclusions. The local kinematics of the thin disc rotation as determined in the framework of our new careful analysis does not favour the presence of a massive overdensity ring just outside the solar radius. We also find values for solar peculiar motion, radial scale lengths of thick disc, and three thin disc populations of different metallicities as a side result of this work.

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Searching for a kinematic signature of the moderately metal-poor stars in the Milky Way bulge using N-body simulations

Astronomy and Astrophysics ◽

10.1051/0004-6361/201732568 ◽

2018 ◽

Vol 615 ◽

pp. A100 ◽

Cited By ~ 5

Author(s):

A. Gómez ◽

P. Di Matteo ◽

M. Schultheis ◽

F. Fragkoudi ◽

M. Haywood ◽

...

Keyword(s):

Milky Way ◽

Thin Disk ◽

Secular Evolution ◽

Thick Disc ◽

Thin Disc ◽

The Mean ◽

The Difference ◽

Different Origins ◽

Argos Data ◽

Internal Evolution

Although there is consensus that metal-rich stars in the Milky Way bulge are formed via secular evolution of the thin disc, the origin of their metal-poor counterparts is still under debate. Two different origins have been invoked for metal-poor stars: they might be classical bulge stars or stars formed via internal evolution of a massive thick disc. We use N-body simulations to calculate the kinematic signature given by the difference in the mean Galactocentric radial velocity (ΔVGC) between metal-rich stars ([Fe/H] ≥ 0) and moderately metal-poor stars (–1.0 ≤ [Fe/H] < 0) in two models, one containing a thin disc and a small classical bulge (B/D = 0.1), and the other containing a thin disc and a massive centrally concentrated thick disc. We reasonably assume that thin-disk stars in each model may be considered as a proxy of metal-rich stars. Similarly, bulge stars and thick-disc stars may be considered as a proxy of metal-poor stars. We calculate ΔVGC at different latitudes (b = 0°, − 2°, − 4°, − 6°, − 8° and − 10°) and longitudes (l = 0°, ± 5°, ± 10° and ± 15°) and show that the ΔVGC trends predicted by the two models are different. We compare the predicted results with ARGOS data and APOGEE DR13 data and show that moderately metal-poor stars are well reproduced with the co-spatial stellar discs model, which has a massive thick disc. Our results give more evidence against the scenario that most of the metal-poor stars are classical bulge stars. If classical bulge stars exists, most of them probably have metallicities [Fe/H] < –1 dex, and their contribution to the mass of the bulge should be a small percentage of the total bulge mass.

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The completeness of Gaia-selected samples of white dwarfs

Proceedings of the International Astronomical Union ◽

10.1017/s1743921320000319 ◽

2019 ◽

Vol 15 (S357) ◽

pp. 170-174

Author(s):

Terry D. Oswalt ◽

Jay B. Holberg ◽

Edward M. Sion

Keyword(s):

White Dwarf ◽

Proper Motion ◽

White Dwarfs ◽

Color Index ◽

Apparent Magnitude ◽

Order Of Magnitude ◽

Gaia Dr2 ◽

Photometric Color

AbstractThe Gaia DR2 has dramatically increased the ability to detect faint nearby white dwarfs. The census of the local white dwarf population has recently been extended from 25 pc to 50 pc, effectively increasing the sample by roughly an order of magnitude. Here we examine the completeness of this new sample as a function of variables such as apparent magnitude, distance, proper motion, photometric color index, unresolved components, etc.

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Analysis of the disc components of our galaxy via kinematic and spectroscopic procedures

Publications of the Astronomical Society of Australia ◽

10.1017/pasa.2019.39 ◽

2019 ◽

Vol 36 ◽

Cited By ~ 3

Author(s):

S. Karaali ◽

S. Bilir ◽

E. Yaz Gökçe ◽

O. Plevne

Keyword(s):

High Probability ◽

Space Velocity ◽

Total Space ◽

Apparent Magnitude ◽

Galactic Latitude ◽

Thick Disc ◽

Thin Disc ◽

Different Populations ◽

Low Probability ◽

The Rich

Abstract We used the spectroscopic and astrometric data provided from the GALactic Archaeology with HERMES (GALAH) Data Release (DR2) and Gaia DR2, respectively, for a large sample of stars to investigate the behaviour of the [ $\alpha$ /Fe] abundances via two procedures, that is, kinematically and spectroscopically. With the kinematical procedure, we investigated the distribution of the [ $\alpha$ /Fe] abundances into the high-/low-probability thin disc, and high-/low-probability thick-disc populations in terms of total space velocity, [Fe/H] abundance, and age. The high-probability thin-disc stars dominate in all sub-intervals of [ $\alpha$ /Fe], including the rich ones: [ $\alpha$ /Fe] $\,>\,0.3$ dex, where the high-probability thick-disc stars are expected to dominate. This result can be explained by the limiting apparent magnitude of the GALAH DR2 ( $V \lt 14$ mag) and intermediate galactic latitude of the star sample. Stars in the four populations share equivalent [ $\alpha$ /Fe] and [Fe/H] abundances, total space velocities, and ages. Hence, none of these parameters can be used alone for separation of a sample of stars into different populations. High-probability thin-disc stars with abundance $-1.3 \lt {\rm[Fe/H]}\leq -0.5$ dex and age $9 \lt \tau\leq13$ Gyr are assumed to have different birth places relative to the metal-rich and younger ones. With the spectroscopic procedure, we separated the sample stars into $\alpha$ -rich and $\alpha$ -poor categories by means of their ages as well as their [ $\alpha$ /Fe] and [Fe/H] abundances. Stars older than 8 Gyr are richer in [ $\alpha$ /Fe] than the younger ones. We could estimate the abundance [ $\alpha$ /Fe] = 0.14 dex as the boundary separating the $\alpha$ -rich and $\alpha$ -poor sub-samples in the [ $\alpha$ /Fe] $\,\times\,$ [Fe/H] plane.

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The dust never settles: collisional production of gas and dust in evolved planetary systems

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1688 ◽

2020 ◽

Vol 496 (4) ◽

pp. 5233-5242 ◽

Cited By ~ 2

Author(s):

Andrew Swan ◽

Jay Farihi ◽

Thomas G Wilson ◽

Steven G Parsons

Keyword(s):

Time Scales ◽

White Dwarf ◽

Dust Emission ◽

Canonical Model ◽

Minor Planets ◽

Infrared Photometry ◽

Dust Production ◽

Thick Disc ◽

Observed Behaviour ◽

Host Stars

ABSTRACT Multi-epoch infrared photometry from Spitzer is used to monitor circumstellar discs at white dwarfs, which are consistent with disrupted minor planets whose debris is accreted and chemically reflected by their host stars. Widespread infrared variability is found across the population of 37 stars with two or more epochs. Larger flux changes occur on longer time-scales, reaching several tens of per cent over baselines of a few years. The canonical model of a geometrically thin, optically thick disc is thus insufficient, as it cannot give rise to the observed behaviour. Optically thin dust best accounts for the variability, where collisions drive dust production and destruction. Notably, the highest infrared variations are seen in systems that show Ca ii emission, supporting planetesimal collisions for all known debris discs, with the most energetic occurring in those with detected gaseous debris. The sample includes the only polluted white dwarf with a circumbinary disc, where the signal of the day–night cycle of its irradiated substellar companion appears diluted by dust emission.

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The tale of the tail – disentangling the high transverse velocity stars in Gaia DR2

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa077 ◽

2020 ◽

Vol 492 (3) ◽

pp. 3816-3828 ◽

Cited By ~ 11

Author(s):

João A S Amarante ◽

Martin C Smith ◽

Corrado Boeche

Keyword(s):

Transverse Velocity ◽

Kinematic Model ◽

Double Sequence ◽

Good Match ◽

Galactic Disc ◽

Thick Disc ◽

Resonant Orbits ◽

Halo Stars ◽

Stellar Halo ◽

Gaia Dr2

ABSTRACT Although the stellar halo accounts for just ∼1 per cent of the total stellar mass of the Milky Way, the kinematics of halo stars encode valuable information about the origins and evolution of our Galaxy. It has been shown that the high transverse velocity stars in Gaia DR2 reveal a double sequence in the Hertzsprung–Russell (HR) diagram, indicating a bifurcation in the local stellar halo within 1 kpc. We fit these stars by updating the popular Besançon/Galaxia model, incorporating the latest observational results for the stellar halo and an improved kinematic description for the thick disc from Schönrich & Binney (2012). We are able to obtain a good match to the Gaia data and provide new constraints on the properties of the Galactic disc and stellar halo. In particular, we show that the kinematically defined thick-disc contribution to this high velocity tail is $\approx 13{{\ \rm per\ cent}}$. We look in greater detail using chemistry from LAMOST DR5, identifying a population of retrograde stars with thick-disc chemistry. Our thick-disc kinematic model cannot account for this population and so we conclude there is likely to be a contribution from heated or accreted stars in the Solar Neighbourhood. We also investigate proposed dynamical substructures in this sample, concluding that they are probably due to resonant orbits rather than accreted populations. Finally, we provide new insights on the nature of the two sequences and their relation with past accretion events and the primordial Galactic disc.

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