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 A New Sample of Thick Disk and Halo Stars

1995 ◽  
Vol 164 ◽  
pp. 386-386
Author(s):  
C. Soubiran ◽  
M.N. Perrin ◽  
R. Cayrel ◽  
E. Chereul
Keyword(s):  
Stellar Population ◽  
Thin Disk ◽  
Thick Disk ◽  
The Other ◽  
Chemical Characteristics ◽  
Fundamental Parameters ◽  
Halo Stars ◽  
Synthetic Spectra ◽  
The Galaxy ◽  
Comparison Stars

The aim of our stellar population study is to investigate the kinematical and chemical characteristics of the thin disk, thick disk and halo of the Galaxy. We have selected 51 stars in 2 astrometric and photometric surveys at l = 42°, b = +79° (Soubiran 1992) and l = 167°, b = +47° (Ojha et al. 1994), on the basis of the Reduced Proper Motion Diagram. They were observed with the 193cm telescope at Observatoire de Haute-Provence, with the CARELEC spectrograph (dispersion of 66Å/mm, FWHM of 3.0Å, range λλ4600 – 5500Å), together with 43 comparison stars with known fundamental parameters. The derivation of Teff, logg and [Fe/H] was done differentially using a grid of synthetic spectra and the comparison stars, as described in Cayrel et al. (1991). Twenty of the target stars were found to be more deficient than −0.5. In the (V, [Fe/H]) distribution, the halo stars are clearly separated from the other stars with a mean of (V, [Fe/H]) ≃ (−210km/s, – 1.4dex). Because of the small size of the sample, it was not possible to discriminate the thick disk from the thin disk. We have taken 200 more spectra, and with these new observations, we hope to be able to deconvolve the 3 populations in the (U, V, W, [Fe/H]) space as we did previously with the (U, V) velocity (Soubiran 1993).

scholarly journals Astrometric Plate Reduction with Orthogonal Functions and Milliarcseconds Accuracy in Deep Proper Motion Surveys

1995 ◽  
Vol 166 ◽  
pp. 368-368
Author(s):  
Devendra Ojha ◽  
Olivier Bienaymé
Keyword(s):  
Galactic Plane ◽  
Structural Parameters ◽  
Thin Disk ◽  
Scale Height ◽  
Thick Disk ◽  
Sample Survey ◽  
Time Base ◽  
List Type ◽  
Proper Motions ◽  
Velocity Dispersions

We have been doing a sample survey in UBV photometry and proper motions as part of an investigation of galactic structure and evolution. The 3 fields in the direction of galactic anticentre (l = 167°, b = 47°), centre (l = 3°, b = 47°) and antirotation (l = 278°, b = 47°) have been surveyed. The high astrometric quality of the MAMA machine (CAI, Paris) gives access to micronic accuracy (leading to < 2 mas per year) on proper motions with a 35 years time base. The kinematical distribution of F and G–type stars have been probed to distances up to 2.5 kpc above the galactic plane. We have derived the constrain on the structural parameters of the thin and thick disk components of the Galaxy (Ojha et al. 1994abc): • The scale lengths of the thin and thick disks are found to be 2.6±0.1 and 3.3±0.5 kpc, respectively. The density laws for stars with 3.5≤MV≤5 as a function of distance above the plane follow a single exponential with scale height of ∼ 260 pc (thin disk) and a second exponential with scale height of ∼ 800 pc (thick disk) with a local normalization of 5–6% of the disk.• The thin disk population was found with (〈 U+W〉, 〈V〉) = (1±4, −14±2) km/s and velocity dispersions (σU+W, σV) = (35±2, 30±1) km/s. The thick disk population was found to have a rotational velocity of Vrot = 177 km/s and velocity dispersions (σU, σV, σW) = (67,51,42) km/s. No dependence with r and z distances was found in the asymmetric drift measurements of the thick disk population.

scholarly journals Chemical Analysis of B stars within 9–11 kpc from the Galactic Center

2009 ◽  
Vol 5 (S265) ◽  
pp. 362-363
Author(s):  
Maria Isela Zevallos Herencia ◽  
Simone Daflon
Keyword(s):  
Chemical Analysis ◽  
Galactic Center ◽  
Thin Disk ◽  
Open Clusters ◽  
The Other ◽  
Galactocentric Distance ◽  
B Stars ◽  
Ob Stars ◽  
Other Hand ◽  
Chemical Distribution

AbstractRadial gradients of metallicity are supported by observations of different young objects in the Galactic thin disk. The shape of the abundance distributions, however, is not completely constrained. Some works describe the abundance distributions as a function of the Galactocentric distance RG by linear fits with a single slope. On the other hand some analyses of open clusters, cepheids and OB stars suggest a discontinuity in the abundance distributions around RG=10 kpc. In this work we analyse a sample of 13 B stars members of four open clusters located within RG=9-11 kpc in order to better constrain the chemical distribution in this region of the disk.

scholarly journals The transition between the thick and thin Galactic disks

2007 ◽  
Vol 3 (S248) ◽  
pp. 458-461
Author(s):  
M. Haywood
Keyword(s):  
Stellar Populations ◽  
Thin Disk ◽  
Solar Neighbourhood ◽  
Galactic Disks ◽  
Local Data ◽  
Galactocentric Distance ◽  
The Status ◽  
Solar Galactocentric Distance ◽  
Thick Disks ◽  
Thin Disks

AbstractWe study the transition between the thick and thick disks using solar neighbourhood data, focusing in particular on the status of local metal-poor thin disk stars ([Fe/H]<−0.3 dex, [α/Fe]<0.1 dex). The orbital properties of these stars, which are responsible for the hiatus in metallicity between the two disks, suggest that they most likely originate from the outer Galactic thin disk. It implies that the transition between the two stellar populations at a solar galactocentric distance must have occurred at a metallicity of about −0.3 dex. Transition stars at this metallicity are in fact present in local samples and fill the gap in α-element between the thick and thin disks. These results imply that, at least from the local data, there is a clear evolutionary link between the thick and thin disks.

Rotating Disks Made from Materials with Negative Poisson's Ratio

2013 ◽  
Vol 804 ◽  
pp. 347-352 ◽  
Author(s):  
Teik Cheng Lim
Keyword(s):  
Maximum Stress ◽  
Anomalous Behavior ◽  
Thin Disk ◽  
Thick Disk ◽  
Rotating Disks ◽  
Disk Material ◽  
Auxetic Materials ◽  
Thin Disks ◽  
Maximum Stresses ◽  
Poissons Ratio

Auxetic materials are those that exhibit negative Poissons ratio. In spite of their rarity, auxetic materials have been artificially produced and also found to exist are known to exist naturally. Arising from their anomalous behavior, research on auxetic materials has been carried out for possible applications in fields as diverse as biomechanics and aero-structures. This paper investigates the effect of auxeticity on the maximum stress in thin and thick rotating disks. The obtained results show that maximum stresses are lower in rotating thin disks that are made from negative Poissons ratio materials. It is also revealed that the maximum stresses in thick rotating disks can be reasonably approximated by rotating thin disk theory if the thick disk material possesses negative Poissons ratio.

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 Exploration of Galactic Structures beyond the Sun toward the anti-center of the Milky Way

2013 ◽  
Vol 9 (S298) ◽  
pp. 450-450
Author(s):  
Yan Xu ◽  
Heidi Newberg
Keyword(s):  
Milky Way ◽  
Galactic Plane ◽  
Wave Structure ◽  
Thin Disk ◽  
Thick Disk ◽  
The Sun ◽  
The South ◽  
The North ◽  
Metallicity Distribution ◽  
Kinematic Distribution

AbstractWe map the stellar distribution on Hess diagram in the Anti-Center roughly in the boxes 130<l<230, −30<b<−10 and 10<b<30. There are ‘extra components’ associated with the anti-center structures of figure 1 of Newberg et al. (2002). The turnoff point of the structure in the North sky is at 16m.5 and the turnoff point in the South is at 17m.5. In our work, these structures can be found in all of the longitude in our box that can't be explained by standard thin or thick disk models. The distance of the North structure is about 2 kpc (we call it the North near structure) and the galactic height is about 0.7 kpc, the distance of the South structure is about 4 – 6 kpc (we call it the South middle structure). The Vgsr distribution of stars selected along the North near structure has a kinematic distribution similar to that of thick disk stars. But the metallicities of these stars are quite similar to the metallicity distribution of thin disk stars. We try to explain these structures with wave structure of the Galactic plane.

scholarly journals M31’s Disk System of Globular Clusters

2005 ◽  
Vol 13 ◽  
pp. 165-166
Author(s):  
Heather Morrison ◽  
Paul Harding ◽  
Denise Hurley-Keller ◽  
Kathy Perrett
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Cluster Formation ◽  
Spectroscopic Studies ◽  
Thin Disk ◽  
Thick Disk ◽  
Galaxy Mergers ◽  
Disk System ◽  
Minor Mergers ◽  
Thin Disks

AbstractGlobular cluster systems are often thought to be associated with violent formation events such as galaxy mergers or the formation of large bulges. However, formation in relatively ordered regions such as thin disks may also be an important process which has been overlooked.Recent high-quality spectroscopic studies of the M31 globulars show that a significant number of the clusters projected on its disk belong to a rapidly rotating thin disk. This contrasts strongly with the Milky Way system, which is composed of a halo and thick disk system and has no known thin disk globulars. It is also likely that M31 has experienced no minor mergers since the globular cluster formation epoch, as such a merger would have heated the globulars into a thick disk system. The metallicity distributions of the disk and non-disk clusters are quite similar.

Non-LTE Abundances of Sodium in the Atmospheres of Red Giants of the Thick and Thin Galactic Disks

2013 ◽  
Vol 9 (S298) ◽  
pp. 394-394
Author(s):  
Sofya Alexeeva ◽  
Yury Pakhomov ◽  
Lyudmila Mashonkina
Keyword(s):  
Thin Disk ◽  
Thick Disk ◽  
Red Giants ◽  
Galactic Disks

AbstractWe determined NLTE abundances of Na in the atmospheres of 80 red giants including the 33 stars of the thin disk, 35 stars of the thick disk and 12 stars of Hercules stream.

scholarly journals The chemical evolution of the Galactic thick and thin disks

2008 ◽  
Vol 4 (S254) ◽  
pp. 191-196 ◽  
Author(s):  
Cristina Chiappini
Keyword(s):  
Chemical Evolution ◽  
Abundance Ratio ◽  
Thin Disk ◽  
Thick Disk ◽  
Disk Evolution ◽  
Gas Accretion ◽  
Main Ideas ◽  
Thin Disks ◽  
Formation Efficiency

AbstractRecent data have revealed a clear distinction between the abundance patterns of the Milky Way (MW) thick and thin disks, suggesting a different origin for each of these components. In this work we first review the main ideas on the formation of the thin disk. From chemical evolution arguments we show that the thin disk should have formed on a long timescale. We also show clear signs that the local stellar samples are contaminated by stars coming from inner radii. We then check what would have to be changed in such a model in order to explain the observables in the thick disk. We find that a model in which the thick disk forms on a much shorter timescale than thin disk and with a star formation efficiency of around a factor of 10 larger than that in the thin disk can account for the observed abundance ratio shifts of several elements between thick and thin disk stars. Moreover, the lack of scatter in the abundance ratio patterns of both the thick and thin disks suggest both components to have been formed in situ by gas accretion and not by mergers of smaller stellar systems. Especially for the thick disk, this last constraint becomes a strong one if its metallicity distribution extends to, at least, solar. Finally, we briefly discuss the interplay between present deuterium abundance and present infall rates in connection with the thin disk evolution.

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