A new study on the thick disk population component of the Galaxy

2000 ◽  
Vol 43 (1) ◽  
pp. 104-112 ◽  
Author(s):  
Jianxiang Rong ◽  
R. Buser
Keyword(s):  
Thick Disk ◽  
The Galaxy ◽  
Population Component

scholarly journals The Age of Old Galactic Populations

1998 ◽  
Vol 11 (1) ◽  
pp. 560-561
Author(s):  
M. Grenon
Keyword(s):  
High Velocity ◽  
Radial Velocities ◽  
Thick Disk ◽  
Early Evolution ◽  
Galactic Bulge ◽  
Colour Class ◽  
The Galaxy ◽  
Nearby Stars

As a preparation to the HIPPARCOS mission, a large observing programme on NLTT stars (propermotion > 0.18 ″/yr) was started in Genevaphotometry. The original programme consists of 10047 stars brighter than mR = 11.5, or mR = 12.5 if of colour class m. Among them, 7813 targets could be included in the HIPPARCOS programme, selected according to their observability and internal priorities in favour of large parallaxe stars (photometric distances < 100 pc) and high-velocity stars. The bulk of new nearby, halo, mild-metal poor and SMR stars in the HIP Catalogue originates from this proposal (N° 139). No less than 208 new nearby stars with π ≥ 40 mas were discovered south of δ +10°, the closest has π(HIP)= 182 mas. Radial velocities were obtained with CORAVEL at OHP and ESO. Most aspects of the early evolution of the Galaxy may be addressed with this sample. Here we discuss, as examples, the ages of the thick disk and of the galactic bulge.

scholarly journals The chemical fingerprints of the thin and the thick disk

2008 ◽  
Vol 4 (S254) ◽  
pp. 197-202
Author(s):  
Sofia Feltzing ◽  
Sally Oey ◽  
Thomas Bensby
Keyword(s):  
Past History ◽  
Thick Disk ◽  
Chemical Abundance ◽  
Dwarf Stars ◽  
Abundance Patterns ◽  
The Galaxy ◽  
Thin And Thick Disks ◽  
Thick Disks ◽  
Definition Of ◽  
Galactic Stellar Populations

AbstractThe past history and origin of the different Galactic stellar populations are manifested in their different chemical abundance patterns. We obtained new elemental abundances for 553 F and G dwarf stars, to more accurately quantify these patterns for the thin and thick disks. However, the exact definition of disk membership is not straightforward. Stars that have a high likelihood of belonging to the thin disk show different abundance patterns from those for the thick disk. In contrast, we show that stars for the Hercules Stream do not show unique abundance patterns, but rather follow those of the thin and thick disks. This strongly suggests that the Hercules Stream is a feature induced by internal dynamics within the Galaxy rather than the remnant of an accreted satellite.

scholarly journals THE THICK DISK IN THE GALAXY NGC 4244 FROM S4G IMAGING

2011 ◽  
Vol 729 (1) ◽  
pp. 18 ◽  
Author(s):  
Sébastien Comerón ◽  
Johan H. Knapen ◽  
Kartik Sheth ◽  
Michael W. Regan ◽  
Joannah L. Hinz ◽  
...  
Keyword(s):  
Thick Disk ◽  
The Galaxy

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 Solar Neighbourhood Age–Metallicity Relation Based on Hipparcos Data

2004 ◽  
Vol 21 (2) ◽  
pp. 121-125 ◽  
Author(s):  
Akihiko Ibukiyama
Keyword(s):  
Star Formation ◽  
Essential Feature ◽  
Formation Rate ◽  
Vertical Gradient ◽  
Thin Disk ◽  
Thick Disk ◽  
Solar Neighbourhood ◽  
Orbital Parameters ◽  
The Galaxy ◽  
The One

AbstractWe derive age–metallicity relations (AMRs) and orbits for the 1658 solar neighbourhood stars for which accurate distances are measured by the Hipparcos satellite. The sample comprises 1382 thin disk stars, 229 thick disk stars, and 47 halo stars according to their orbital parameters. We find a considerable scatter for thin disk AMRs along the one-zone Galactic chemical evolution (GCE) model. Orbits and metallicities of thin disk stars show no clear relation to each other. The scatter along the AMR exists even if stars with the same orbits are selected. We examine simple extensions of one-zone GCE models which account for inhomogeneity in the effective yield and inhomogeneous star formation rate in the Galaxy. Both extensions of the one-zone GCE model cannot account for the scatter in the age–[Fe/H]–[Ca/Fe] relation simultaneously. We conclude, therefore, that the scatter along the thin disk AMR is an essential feature in the formation and evolution of the Galaxy. The AMR for thick disk stars shows that star formation terminated 8 Gyr ago in the thick disk. As previously reported, thick disk stars are more Ca-rich than thin disk stars with the same [Fe/H]. We find that thick disk stars show a vertical abundance gradient. These three facts — AMR, vertical gradient, and [Ca/Fe]–[Fe/H] relation — support monolithic collapse and/or accretion of satellite dwarf galaxies as likely thick disk formation scenarios.

scholarly journals Streams, Substructures, and the Early History of the Milky Way

2020 ◽  
Vol 58 (1) ◽  
pp. 205-256 ◽  
Author(s):  
Amina Helmi
Keyword(s):  
Star Formation ◽  
Phase Space ◽  
Milky Way ◽  
Current Knowledge ◽  
Thick Disk ◽  
Age Dating ◽  
Wide Field ◽  
Chemical Labeling ◽  
The Galaxy ◽  
Hydrodynamical Simulations

The advent of the second data release of the Gaia mission, in combination with data from large spectroscopic surveys, is revolutionizing our understanding of the Galaxy. Thanks to these transformational data sets and the knowledge accumulated thus far, a new, more mature picture of the evolution of the early Milky Way is currently emerging. ▪  Two of the traditional Galactic components, namely, the stellar halo and the thick disk, appear to be intimately linked: Stars with halo-like kinematics originate in similar proportions from a heated (thick) disk and from debris from a system named Gaia-Enceladus. Gaia-Enceladus was the last big merger event experienced by the Milky Way and was completed around 10 Gyr ago. The puffed-up stars now present in the halo as a consequence of the merger have thus exposed the existence of a disk component at z ∼ 1.8. This is likely related to the previously known metal-weak thick disk and may be traceable to metallicities [Fe/H] [Formula: see text] −4. As importantly, there is evidence that the merger with Gaia-Enceladus triggered star formation in the early Milky Way, plausibly leading to the appearance of the thick disk as we know it. ▪  Other merger events have been characterized better, and new ones have been uncovered. These include, for example, the Helmi streams, Sequoia, and Thamnos, which add to the list of those discovered in wide-field photometric surveys, such as the Sagittarius streams. Current knowledge of their progenitors’ properties, star formation, and chemical evolutionary histories is still incomplete. ▪  Debris from different objects shows different degrees of overlap in phase-space. This sometimes confusing situation can be improved by determining membership probabilities via quantitative statistical methods. A task for the next few years will be to use ongoing and planned spectroscopic surveys for chemical labeling and to disentangle events from one another using dimensions other than phase-space, metallicity, or [α/Fe]. ▪  These large surveys will also provide line-of-sight velocities missing for faint stars in Gaia releases and more accurate distance determinations for distant objects, which in combination with other surveys could also lead to more accurate age dating. The resulting samples of stars will cover a much wider volume of the Galaxy, allowing, for example, the linking of kinematic substructures found in the inner halo to spatial overdensities in the outer halo. ▪  All the results obtained so far are in line with the expectations of current cosmological models. Nonetheless, tailored hydrodynamical simulations to reproduce in detail the properties of the merger debris, as well as constrained cosmological simulations of the Milky Way, are needed. Such simulations will undoubtedly unravel more connections between the different Galactic components and their substructures, and will aid in pushing our knowledge of the assembly of the Milky Way to the earliest times.

scholarly journals THE FREQUENCY OF FIELD BLUE-STRAGGLER STARS IN THE THICK DISK AND HALO SYSTEM OF THE GALAXY

2015 ◽  
Vol 801 (2) ◽  
pp. 116 ◽  
Author(s):  
Rafael M. Santucci ◽  
Vinicius M. Placco ◽  
Silvia Rossi ◽  
Timothy C. Beers ◽  
Henrique M. Reggiani ◽  
...  
Keyword(s):  
Thick Disk ◽  
Blue Straggler ◽  
The Galaxy
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