scholarly journals Moving Groups in the Galactic Disc

2013 ◽  
Vol 9 (S298) ◽  
pp. 77-82
Author(s):  
P. Ramya ◽  
B. E. Reddy
Keyword(s):  
Open Clusters ◽  
Galactic Disc ◽  
Chemical Abundance ◽  
Abundance Pattern ◽  
Thick Disc ◽  
Thin Disc ◽  
Stellar Streams ◽  
Moving Groups ◽  
Rule Out

AbstractWe present results of chemical abundance study of a few representative stellar streams of Galactic thick and thin discs. Arcturus stream, which was proposed to have an extragalactic origin, and a recently detected stream called AF06 were studied. Results show a range of metallicity, age and abundance pattern that are consistent with those of Galactic thick disc component. We found similar results for AF06. The abundance and age results unambiguously rule out the possibility that the member stars are vestiges of open clusters. Abundance results of a sample of stars of Sirius and Hercules streams combined with the kinematics show that both the streams belong to the thin disc component. Also, results rule out these are remnants of open clusters. It is likely these streams formed insitu due to perturbations caused by non-axisymmetric components such as bar or spirals.

scholarly journals Nitrogen evolution in the halo, thick disc, thin disc, and bulge of the Galaxy

2021 ◽  
Vol 508 (1) ◽  
pp. 719-727
Author(s):  
V Grisoni ◽  
F Matteucci ◽  
D Romano
Keyword(s):  
Galactic Halo ◽  
Massive Stars ◽  
Chemical Elements ◽  
Distribution Functions ◽  
Abundance Pattern ◽  
Origin And Evolution ◽  
Thick Disc ◽  
Thin Disc ◽  
Abundance Patterns ◽  
The Galaxy

ABSTRACT We study the evolution of nitrogen (N) in the Galactic halo, thick disc, thin disc, and bulge by comparing detailed chemical evolution models with recent observations. The models used in this work have already been constrained to explain the abundance patterns of α-elements and the metallicity distribution functions of halo, disc, and bulge stars; here, we adopt them to investigate the origin and evolution of N in the different Galactic components. First, we consider different sets of yields and study the importance of the various channels proposed for N production. Secondly, we apply the reference models to study the evolution of both the Galactic discs and bulge. We conclude that: i) primary N produced by rotating massive stars is required to reproduce the plateau in log(N/O) and [N/Fe] ratios at low metallicity, as well as the secondary and primary production from low- and intermediate-mass stars to reproduce the data of the thin disc; ii) the parallel model can provide a good explanation of the evolution of N abundance in the thick and thin discs, and we confirm that the thick disc has evolved much faster than the thin disc, in agreement with the results from the abundance patterns of other chemical elements; and iii) finally, we present new model predictions for N evolution in the Galactic bulge, and we show that the observations in bulge stars can be explained if massive stars rotate fast during the earliest phases of Galactic evolution, in agreement with findings from the abundance pattern of carbon.

scholarly journals Planetary mass–radius relations across the galaxy

2020 ◽  
Vol 639 ◽  
pp. A66 ◽  
Author(s):  
A. Michel ◽  
J. Haldemann ◽  
C. Mordasini ◽  
Y. Alibert
Keyword(s):  
Bulk Composition ◽  
Chemical Species ◽  
Stellar Populations ◽  
Chemical Abundance ◽  
Thick Disc ◽  
Thin Disc ◽  
Planetary Mass ◽  
The Galaxy ◽  
Galactic Stellar Populations ◽  
Internal Structure Models

Context. Planet formation theory suggests that planet bulk compositions are likely to reflect the chemical abundance ratios of their host star’s photosphere. Variations in the abundance of particular chemical species in stellar photospheres between different galactic stellar populations demonstrate that there are differences among the expected solid planet bulk compositions. Aims. We aim to present planetary mass-radius relations of solid planets for kinematically differentiated stellar populations, namely, the thin disc, thick disc, and halo. Methods. Using two separate internal structure models, we generated synthetic planets using bulk composition inputs derived from stellar abundances. We explored two scenarios, specifically iron-silicate planets at 0.1 AU and silicate-iron-water planets at 4 AU. Results. We show that there is a persistent statistical difference in the expected mass-radius relations of solid planets among the different galactic stellar populations. At 0.1 AU for silicate-iron planets, there is a 1.51–2.04% mean planetary radius difference between the thick and thin disc stellar populations, whilst for silicate-iron-water planets past the ice line at 4 AU, we calculate a 2.93–3.26% difference depending on the models. Between the halo and thick disc, we retrieve at 0.1 AU a 0.53–0.69% mean planetary radius difference, and at 4 AU we find a 1.24–1.49% difference depending on the model. Conclusions. Future telescopes (such as PLATO) will be able to precisely characterize solid exoplanets and demonstrate the possible existence of planetary mass-radius relationship variability between galactic stellar populations.

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

2018 ◽  
Vol 619 ◽  
pp. A143 ◽  
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.

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

2018 ◽  
Vol 614 ◽  
pp. A63 ◽  
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.

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

2018 ◽  
Vol 615 ◽  
pp. A100 ◽  
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.

scholarly journals The age–chemical abundance structure of the Galactic disc – II. α-dichotomy and thick disc formation

2020 ◽  
Vol 497 (2) ◽  
pp. 2371-2384 ◽  
Author(s):  
Jianhui Lian ◽  
Daniel Thomas ◽  
Claudia Maraston ◽  
Timothy C Beers ◽  
Christian Moni Bidin ◽  
...  
Keyword(s):  
Star Formation ◽  
Cosmic Time ◽  
Theoretical Models ◽  
Bimodal Distribution ◽  
Chemical Abundance ◽  
Secular Evolution ◽  
Thick Disc ◽  
Star Formation Activity ◽  
Gas Accretion ◽  
Disc Formation

ABSTRACT We extend our previous work on the age–chemical abundance structure of the Galactic outer disc to the inner disc (4 &lt; r &lt; 8  kpc) based on the SDSS/APOGEE survey. Different from the outer disc, the inner disc stars exhibit a clear bimodal distribution in the [Mg/Fe]–[Fe/H] plane. While a number of scenarios have been proposed in the literature, it remains challenging to recover this bimodal distribution with theoretical models. To this end, we present a chemical evolution model embedding a complex multiphase inner disc formation scenario that matches the observed bimodal [Mg/Fe]–[Fe/H] distribution. In this scenario, the formation of the inner disc is dominated by two main starburst episodes $6\,$Gyr apart with secular, low-level star formation activity in between. In our model, the first starburst occurs at early cosmic times ($t\sim 1\,$ Gyr) and the second one $6\,$ Gyr later at a cosmic time of $t\sim 7\,$ Gyr. Both these starburst episodes are associated with gas accretion events in our model, and are quenched rapidly. The first starburst leads to the formation of the high-α sequence, and the second starburst leads to the formation of the metal-poor low-α sequence. The metal-rich low-α stars, instead, form during the secular evolution phase between the two bursts. Our model shows that the α-dichotomy originates from the rapid suppression of star formation after the first starburst. The two starburst episodes are likely to be responsible for the formation of the geometric thick disc (z &gt;1 kpc), with the old inner thick disc and the young outer thick disc forming during the first and the second starbursts, respectively.

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

2019 ◽  
Vol 36 ◽  
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.

scholarly journals A comprehensive tool for the statistical comparison of Large Surveys to Models of the Galaxy

2013 ◽  
Vol 9 (S298) ◽  
pp. 92-97
Author(s):  
Andreas Ritter
Keyword(s):  
Radial Velocity ◽  
Statistical Methods ◽  
Large Data ◽  
Data Set ◽  
Statistical Comparison ◽  
Stellar Streams ◽  
The Galaxy ◽  
Comprehensive Comparison ◽  
Moving Groups ◽  
First Time

AbstractThe advent of large spectroscopic surveys of the Galaxy offers the possibility to compare Galactic models to actual measurements for the first time. I have developed a tool for the comprehensive comparison of any large data set to the predictions made by models of the Galaxy using sophisticated statistical methods, and to visualise the results for any given direction. This enables us to point out systematic differences between the model and the measurements, as well as to identify new (sub-)structures in the Galaxy. These results can then be used to improve the models, which in turn will allow us to find even more substructures like stellar streams, moving groups, or clusters. In this paper I show the potential of this tool by applying it to the RAdial Velocity Experiment (RAVE, Steinmetz 2003) and the Besançon model of the Galaxy Robin et al. 2003.

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

2020 ◽  
Vol 492 (3) ◽  
pp. 3816-3828 ◽  
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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