Stellar Populations of the Galactic Disk: Metallicity Distribution and Kinematics

2003 ◽  
Vol 12 (4) ◽  
Author(s):  
S. Bartašiūtė ◽  
Z. Aslan ◽  
R. P. Boyle ◽  
N. V. Kharchenko ◽  
L. P. Ossipkov ◽  
...  
Keyword(s):  
Proper Motion ◽  
Galactic Disk ◽  
Stellar Populations ◽  
Thin Disk ◽  
Radial Velocities ◽  
Thick Disk ◽  
Status Report ◽  
Stellar Content ◽  
Metallicity Distribution

AbstractMetallicities and distances have been determined from Vilnius photometry for an in situ sample of nearly 650 stars in eight proper-motion fields at high Galactic latitudes. For half of these stars, radial velocities have been measured with the CORAVEL spectrometer, which allowed us to derive spatial velocities and Galactic orbits. In this contribution we present a status report on our results for the stellar content of the Galactic disk, with emphasis given to specific aspects of distinguishing the thick-disk stars from the old thin-disk population.

scholarly journals The AMBRE project: The thick thin disk and thin thick disk of the Milky Way

2017 ◽  
Vol 608 ◽  
pp. L1 ◽  
Author(s):  
M. R. Hayden ◽  
A. Recio-Blanco ◽  
P. de Laverny ◽  
S. Mikolaitis ◽  
C. C. Worley
Keyword(s):  
Vertical Velocity ◽  
Velocity Dispersion ◽  
Stellar Populations ◽  
Thin Disk ◽  
Thick Disk ◽  
Solar Neighborhood ◽  
Chemical Enrichment ◽  
History Of ◽  
External Galaxies ◽  
Subgiant Stars

We analyze 494 main sequence turnoff and subgiant stars from the AMBRE:HARPS survey. These stars have accurate astrometric information from Gaia DR1, providing reliable age estimates with relative uncertainties of ±1 or 2 Gyr and allowing precise orbital determinations. The sample is split based on chemistry into a low-[Mg/Fe] sequence, which are often identified as thin disk stellar populations, and high-[Mg/Fe] sequence, which are often associated with thick disk stellar populations. We find that the high-[Mg/Fe] chemical sequence has extended star formation for several Gyr and is coeval with the oldest stars of the low-[Mg/Fe] chemical sequence: both the low- and high-[Mg/Fe] sequences were forming stars at the same time. We find that the high-[Mg/Fe] stellar populations are only vertically extended for the oldest, most-metal poor and highest [Mg/Fe] stars. When comparing vertical velocity dispersion for the low- and high-[Mg/Fe] sequences, the high-[Mg/Fe] sequence has lower vertical velocity dispersion than the low-[Mg/Fe] sequence for stars of similar age. This means that identifying either group as thin or thick disk based on chemistry is misleading. The stars belonging to the high-[Mg/Fe] sequence have perigalacticons that originate in the inner disk, while the perigalacticons of stars on the low-[Mg/Fe] sequence are generally around the solar neighborhood. From the orbital properties of the stars, the high-[Mg/Fe] and low-[Mg/Fe] sequences are most likely a reflection of the chemical enrichment history of the inner and outer disk populations, respectively; radial mixing causes both populations to be observed in situ at the solar position. Based on these results, we emphasize that it is important to be clear in defining what populations are being referenced when using the terms thin and thick disk, and that ideally the term thick disk should be reserved for purely geometric definitions to avoid confusion and be consistent with definitions in external galaxies.

scholarly journals The radial extent of the Galactic thick disk

2016 ◽  
Vol 11 (S321) ◽  
pp. 3-5
Author(s):  
Thomas Bensby
Keyword(s):  
Milky Way ◽  
Galactic Disk ◽  
Thin Disk ◽  
Thick Disk ◽  
Stellar Disk ◽  
Chemical Signatures ◽  
Radial Extent ◽  
Thin And Thick Disks ◽  
Thick Disks ◽  
Scale Length

AbstractBased on observational data from the fourth internal data release of the Gaia-ESO Survey we probe the abundance structure in the Milky Way stellar disk as a function of galactocentric radius and height above the plane. We find that the inner and outer Galactic disks have different chemical signatures. The stars in the inner Galactic disk show abundance signatures of both the thin and thick disks, while the stars in the outer Galactic disk resemble in majority the abundances seen in the thin disk. Assuming that the Galactic thick disk can be associated with the α-enriched population, this can be interpreted as that the thick disk density drops drastically beyond a galactocentric radius of about 10 kpc. This is in agreement with recent findings that the thick disk has a short scale-length, shorter than that of the the thin disk.

scholarly journals The Geneva–Copenhagen Survey of the Solar Neighbourhood

2004 ◽  
Vol 21 (2) ◽  
pp. 129-133 ◽  
Author(s):  
B. Nordström ◽  
J. Andersen ◽  
J. Holmberg ◽  
B. R. Jørgensen ◽  
M. Mayor ◽  
...  
Keyword(s):  
Binary Stars ◽  
Galactic Disk ◽  
Classical Model ◽  
Thin Disk ◽  
Solar Neighbourhood ◽  
Proper Motions ◽  
Kinematic Data ◽  
Model Predictions ◽  
The Mean ◽  
Metallicity Distribution

AbstractWe report on a new survey of metallicities, ages, and Galactic orbits for a complete, magnitude-limited, and kinematically unbiased all-sky sample of 16 682 nearby F- and G-dwarfs. Our ∼ 63 000 new, accurate radial velocities for nearly 13 500 of the stars, combined with Hipparcos parallaxes and Tycho-2 proper motions, complete the kinematic data for 14 139 stars and allow us to identify most of the binary stars in the sample. Isochrone ages have been determined whenever reliable results are possible, with particular attention to realistic error estimates.Among the basic properties of the Galactic disk that can be reinvestigated from our data are the metallicity distribution of G-dwarfs and the age–metallicity and age–velocity relations of the solar neighbourhood. We confirm the lack of metal-poor G-dwarfs relative to classical model predictions (the 'G-dwarf problem'), the near-constancy of the mean metallicity since the formation of the thin disk, and the appearance of the kinematic signature of the thick disk ∼ 10 Gyr ago.

scholarly journals Impacts of Radial Mixing on the Galactic Thick and Thin Disks

2017 ◽  
Vol 13 (S334) ◽  
pp. 132-135
Author(s):  
Daisuke Kawata
Keyword(s):  
Thin Disk ◽  
Scale Height ◽  
Thick Disk ◽  
The Other ◽  
Galactic Disks ◽  
Spiral Arms ◽  
Other Hand ◽  
Initial Scale ◽  
Thin Disks ◽  
Metallicity Distribution

AbstractUsing N-body simulations of the Galactic disks, we qualitatively study how the metallicity distributions of the thick and thin disk stars are modified by radial mixing induced by the bar and spiral arms. We show that radial mixing drives a positive vertical metallicity gradient in the mono-age disk population whose initial scale-height is constant and initial radial metallicity gradient is tight and negative. On the other hand, if the initial disk is flaring, with scale-height increasing with galactocentric radius, radial mixing leads to a negative vertical metallicity gradient, which is consistent with the current observed trend. We also discuss impacts of radial mixing on the metallicity distribution of the thick disk stars. By matching the metallicity distribution of N-body models to the SDSS/APOGEE data, we argue that the progenitor of the Milky Way’s thick disk should not have a steep negative metallicity gradient.

scholarly journals The Galactic Disk-Halo Transition – Evidence from Stellar Abundances

2008 ◽  
Vol 4 (S254) ◽  
pp. 103-108 ◽  
Author(s):  
Poul Erik Nissen ◽  
William J. Schuster
Keyword(s):  
Milky Way ◽  
Galactic Disk ◽  
Thin Disk ◽  
Thick Disk ◽  
Chemical Abundance ◽  
Elemental Abundances ◽  
Halo Stars ◽  
New Information ◽  
First Results ◽  
Satellite Galaxies

AbstractNew information on the relations between the Galactic disks, the halo, and satellite galaxies is being obtained from elemental abundances of stars having metallicities in the range −1.5 < [Fe/H] < −0.5. The first results for a sample of 26 halo stars and 13 thick-disk stars observed with the ESO VLT/UVES spectrograph are presented. The halo stars fall in two distinct groups: one group (9 stars) has [α/Fe] = 0.30 ± 0.03 like the thick-disk stars. The other group (17 stars) shows a clearly deviating trend ranging from [α/Fe] = 0.20 at [Fe/H] = −1.3 to [α/Fe] = 0.08 at [Fe/H] = −0.8. The kinematics of the stars are discussed and the abundance ratios Na/Fe, Ni/Fe, Cu/Fe and Ba/Y are applied to see if the “low-alpha” stars are connected to the thin disk or to Milky Way satellite galaxies. Furthermore, we compare our data with simulations of chemical abundance distributions in hierarchically formed stellar halos in a ΛCDM Universe.

scholarly journals A Titius-Bode like law for stellar populations in the velocity space

2006 ◽  
Vol 2 (S235) ◽  
pp. 68-68
Author(s):  
Santiago Alcobé ◽  
Rafael Cubarsi
Keyword(s):  
Velocity Dispersion ◽  
Energy Levels ◽  
Average Energy ◽  
Maximum Velocity ◽  
Stellar Populations ◽  
Thin Disk ◽  
Thick Disk ◽  
Velocity Space ◽  
Heating Process ◽  
Stellar Velocity

AbstractThe statistical algorithm MEMPHIS (Cubarsi & Alcobé 2006) was applied to a large sample from the Hipparcos catalogue with the full space motions (Cubarsi & Alcobé 2004), to segregate the kinematic populations of the solar neighbourhood. Four stellar populations were obtained, namely early-thin disk, young-thin disk, the whole thin disk (which contains both previous populations plus the continuum of old thin disk stars), and the thick disk population. Now, we wish to point out two main results from the analysis of such a segregation (Alcobé & Cubarsi 2005). First, the relationship between the maximum stellar velocity of a sample and its average age τ can be approximated by the relation |V|max ∝ τ. Second, the local stellar populations can be described from a Titius-Bode like law (TBLL) for the radial velocity dispersion, $\sigma_1 = 6.6 \, (\frac43)^n$, so that for values n = 2, 3, 5, 8 it determines some average energy levels of discrete populations, while for continuous intervals n ≤ 5 and n ≥ 7 it describes the velocity-age evolution of thin and thick disk components, as shown in the Table below.Thus, the velocity dispersions of the local kinematic populations seem to follow a geometrical progression, allowing us to do an analogy with the old Titius-Bode distribution for keplerian orbits, although a physical explanation for the later law remains still open (Lynch 2003). Indeed, such a TBLL in the velocity space could be already conjectured from previous published kinematic parameters of the Galactic components (e.g. Alcobé & Cubarsi 2001). As in the keplerian case, it is possible to argue that velocity dispersion values have too much uncertainty, but, even so, it is not possible to ignore anymore such a resemblance.Such results are consistent with Galactic formation models that predict some quasi-continuous stellar populations in the sense that the continuity is constricted by σ1 levels of the TBLL. The physical meaning of the variable n involved in the TBLL may be related with the average epicycle energy ER ~ σ21 of the stars representative of the disk heating process. It shows continuity from n = 3 to 5 for the thin disk, and from 7 to 8 for the thick disk, but discreteness from n = 2 to 3 between early-thin and young-thin disk, and from 5 to 8 between thin and thick disk components. For the thin disk, for example, the level n = 5 should represent the saturation point of maximum velocity dispersion, likely corresponding to the limited predicted by the observed wavenumber of spiral structure of the Milky Way, while the discontinuity from n = 5 to 7 indicates an abrupt jump in the average energy, that was produced when the thick disk was formed about 10±1 Gyr ago.

scholarly journals On the origin of giant planets and their hosts

2009 ◽  
Vol 5 (S265) ◽  
pp. 434-435
Author(s):  
Misha Haywood
Keyword(s):  
Formation Process ◽  
Planet Formation ◽  
Galactic Disk ◽  
Giant Planet ◽  
Solar Radius ◽  
Thick Disk ◽  
Giant Planets ◽  
Dynamical Effect ◽  
Giant Stars ◽  
Metallicity Distribution

AbstractThe correlation between stellar metallicity and giant planets has been tentatively explained by the possible increase of planet formation probability in stellar disks with enhanced amount of metals. There are two caveats to this explanation. First, giant stars with planets do not show a metallicity distribution skewed towards metal-rich objects, as found for dwarfs. Second, the correlation with metallicity is not valid at intermediate metallicities, for which it can be shown that giant planets are preferentially found orbiting thick disk stars.None of these two peculiarities is explained by the proposed scenarios of giant planet formation. We contend that they are galactic in nature, and probably not linked to the formation process of giant planets. It is suggested that the same dynamical effect, namely the migration of stars in the galactic disk, is at the origin of both features, with the important consequence that most metal-rich stars hosting giant planets originate from the inner disk. A planet-metallicity correlation similar to the observed one is easily obtained if stars from the inner disk have a higher percentage of giant planets than stars born at the solar radius, with no specific dependence on metallicity. We propose that the density of H2 in the inner galactic disk (the molecular ring) could play a role in setting the high percentage of giant planets that originate from this region.

Chemo-Kinematic Properties of the Galactic Disk with SEGUE G and K Dwarfs: Constraints on Formation

2017 ◽  
Vol 13 (S334) ◽  
pp. 306-307
Author(s):  
Doori Han ◽  
Young Sun Lee ◽  
Young Kwang Kim ◽  
Timothy C. Beers
Keyword(s):  
Milky Way ◽  
Velocity Dispersion ◽  
Galactic Disk ◽  
Thin Disk ◽  
Thick Disk ◽  
Formation Mechanisms ◽  
Orbital Eccentricity ◽  
Disk Formation ◽  
Velocity Gradients ◽  
Kinematic Properties

AbstractWe present the derived kinematic characteristics of low-α thin-disk and high-α thick-disk stars in the Milky Way, investigated with a sample of about 32,000 G- and K-type dwarfs from the Sloan Extension for Galactic Understanding and Exploration (SEGUE). Based on the level of α-element enhancement as a function of [Fe/H], we separate our sample into thin- and thick-disk stars and then derive mean velocities, velocity dispersions, and velocity gradients for the U, V, and W velocity components, respectively, as well as the orbital eccentricity distribution. There are notable gradients in the V velocity over [Fe/H] in both populations: −23 km s−1 dex−1 for the thin disk and +44 km s−1 dex−1 for the thick disk. The velocity dispersion of the thick disk decreases with increasing [Fe/H], while the velocity dispersion gradient over [Fe/H] for the thin disk is almost flat for all velocity components, except for the W velocity dispersion of the metal-poor thin-disk stars. The eccentricity distribution exhibits a peak at a higher value, and is more symmetric as [α/Fe] increases, implying that complex formation mechanisms may be involved. Our results can be used to constrain several proposed disk-formation scenarios of the Milky Way and other large spirals.

scholarly journals A systematic study of NLTE abundances of nearby stars

2013 ◽  
Vol 9 (S298) ◽  
pp. 400-400
Author(s):  
Y. Q. Chen ◽  
G. Zhao ◽  
L. Mashonkina ◽  
J. R. Shi ◽  
H. W. Zhang ◽  
...  
Keyword(s):  
Chemical Evolution ◽  
Systematic Study ◽  
Stellar Populations ◽  
Thin Disk ◽  
Thick Disk ◽  
Spectral Lines ◽  
Surface Gravity ◽  
Elemental Abundances ◽  
The Galaxy ◽  
Nearby Stars

AbstractApproximately 80 stars from the thin disk, the thick disk and the halo of the Galaxy, in the range of −3.0 < [Fe/H] < +0.5, surface gravity of 3.0 < logg < 4.7 and temperature of 4500 K < Teff < 6500 K, have been observed with the Shane/Hamilton and CFHT/Espadons spectrographs in order to carry out a systematic NLTE study of nearby stars in a consistent way. We will determine reliably stellar parameters and determine precise elemental abundances via a comprehensive NLTE analysis of the spectral lines of Li, Na, Mg, Al, Si, K, Ca, Sc, Mn, Fe, Sr, Zr, Ba, Nd, and Eu elements. Finally, we aim to investigate the chemical evolution of the Galaxy through different stellar populations based on the NLTE abundances for total 15 elements.

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