STRONTIUM ABUNDANCES IN COOL DWARF STARS OF GALACTIC THIN AND THICK DISKS

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.

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Elemental abundance trends in the Galactic thin and thick disks as traced by nearby F and G dwarf stars

Astronomy and Astrophysics ◽

10.1051/0004-6361:20031213 ◽

2003 ◽

Vol 410 (2) ◽

pp. 527-551 ◽

Cited By ~ 494

Author(s):

T. Bensby ◽

S. Feltzing ◽

I. Lundström

Keyword(s):

Elemental Abundance ◽

Dwarf Stars ◽

Abundance Trends ◽

Thin And Thick Disks ◽

Thick Disks

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Kinematical & Chemical Characteristics of the Thin and Thick Disks

Proceedings of the International Astronomical Union ◽

10.1017/s1743921308027579 ◽

2008 ◽

Vol 4 (S254) ◽

pp. 179-190 ◽

Cited By ~ 2

Author(s):

Rosemary F. G. Wyse

Keyword(s):

Dark Matter ◽

Cold Dark Matter ◽

Milky Way ◽

Observational Evidence ◽

Chemical Characteristics ◽

Chemical Abundance ◽

The Galaxy ◽

History Of ◽

Thin And Thick Disks ◽

Thick Disks

AbstractI discuss how the chemical abundance distributions, kinematics and age distributions of stars in the thin and thick disks of the Galaxy can be used to decipher the merger history of the Milky Way, a typical large galaxy. The observational evidence points to a rather quiescent past merging history, unusual in the context of the ‘consensus’ cold-dark-matter cosmology favoured from observations of structure on scales larger than individual galaxies.

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THE THIN AND THICK DISKS OF THE GALAXY: DIFFERENCES IN EVOLUTION

ISLAND UNIVERSES - Astrophysics and Space Science Proceedings ◽

10.1007/978-1-4020-5573-7_7 ◽

2007 ◽

pp. 53-56

Author(s):

Tetyana V. Nykytyuk ◽

Tamara V. Mishenina

Keyword(s):

The Galaxy ◽

Thin And Thick Disks ◽

Thick Disks

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The radial extent of the Galactic thick disk

Proceedings of the International Astronomical Union ◽

10.1017/s1743921316008875 ◽

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.

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Occurrence rates of small planets from HARPS

Astronomy and Astrophysics ◽

10.1051/0004-6361/202038881 ◽

2020 ◽

Vol 643 ◽

pp. A106

Author(s):

D. Bashi ◽

S. Zucker ◽

V. Adibekyan ◽

N. C. Santos ◽

L. Tal-Or ◽

...

Keyword(s):

Radial Velocity ◽

Detection Limits ◽

Thick Disk ◽

Occurrence Rate ◽

Mass Detection ◽

The Galaxy ◽

Low Mass ◽

Thin And Thick Disks ◽

Thick Disks ◽

Stellar Properties

Context. The stars in the Milky Way thin and thick disks can be distinguished by several properties such as metallicity and kinematics. It is not clear whether the two populations also differ in the properties of planets orbiting the stars. In order to study this, a careful analysis of both the chemical composition and mass detection limits is required for a sufficiently large sample. Currently, this information is still limited only to large radial-velocity (RV) programs. Based on the recently published archival database of the High Accuracy Radial velocity Planet Searcher (HARPS) spectrograph, we present a first analysis of low-mass (small) planet occurrence rates in a sample of thin- and thick-disk stars. Aims. We aim to assess the effects of stellar properties on planet occurrence rates and to obtain first estimates of planet occurrence rates in the thin and thick disks of the Galaxy. As a baseline for comparison, we also aim to provide an updated value for the small close-in planet occurrence rate and compare it with the results of previous RV and transit (Kepler) works. Methods. We used archival HARPS RV datasets to calculate detection limits of a sample of stars that were previously analysed for their elemental abundances. For stars with known planets we first subtracted the Keplerian orbit. We then used this information to calculate planet occurrence rates according to a simplified Bayesian model in different regimes of stellar and planet properties. Results. Our results suggest that metal-poor stars and more massive stars host fewer low-mass close-in planets. We find the occurrence rates of these planets in the thin and thick disks to be comparable. In the iron-poor regimes, we find these occurrence rates to be significantly larger at the high-α region (thick-disk stars) as compared with the low-α region (thin-disk stars). In general, we find the average number of close-in small planets (2–100 days, 1–20M⊕) per star (FGK-dwarfs) to be: n¯p = 0.36 ± 0.05, while the fraction of stars with planets is Fh = 0.23−0.03+0.04. Qualitatively, our results agree well with previous estimates based on RV and Kepler surveys. Conclusions. This work provides a first estimate of the close-in small planet occurrence rates in the solar neighbourhood of the thin and thick disks of the Galaxy. It is unclear whether there are other stellar properties related to the Galactic context that affect small-planet occurrence rates, or if it is only the combined effects of stellar metal content and mass. A future larger sample of stars and planets is needed to address those questions.

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Elemental abundance trends in the metal-rich thin and thick disks

The Metal-Rich Universe ◽

10.1017/cbo9780511536267.006 ◽

2011 ◽

pp. 41-52

Author(s):

S. Feltzing

Keyword(s):

Elemental Abundance ◽

Abundance Trends ◽

Thin And Thick Disks ◽

Thick Disks

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The Chemical Composition of the Galactic Bulge and Implications for its Evolution

Publications of the Astronomical Society of Australia ◽

10.1017/pasa.2016.32 ◽

2016 ◽

Vol 33 ◽

Cited By ~ 39

Author(s):

Andrew McWilliam

Keyword(s):

Time Delay ◽

Chemical Composition ◽

Measurement Errors ◽

Thick Disk ◽

Core Collapse ◽

Vertical Scale ◽

Effective Yield ◽

Type Ia ◽

Thin And Thick Disks ◽

Thick Disks

AbstractAt a bulge latitude of b = −4°, the average [Fe/H] and [Mg/H] values are +0.06 and +0.17 dex, roughly 0.2 and 0.7 dex higher than the local thin and thick disk values, respectively, suggesting a large bulge effective yield, perhaps due to efficient retention of supernova ejecta.The bulge vertical [Fe/H] gradient, at ~ 0.5 dex/kpc, appears to be due to a changing mixture of sub-populations (near +0.3 dex and −0.3 dex and one possibly near −0.7 dex) with latitude. At solar [Fe/H], the bulge [Al/Fe] and [α/Fe] ratios are ~ +0.15 dex. Below [Fe/H] < ![CDATA[$ ~ −0.5 dex, the bulge and local thick disk compositions are very similar; but the measured [Mg/Fe], [⟨SiCaTi⟩/Fe], [La/Eu] and dramatic [Cu/Fe] ratios suggest higher SFR in the bulge. However, these composition differences with the thick disk could be due to measurement errors and non-LTE effects.Unusual zig-zag trends of [Cu/Fe] and [Na/Fe] suggest metallicity-dependent nucleosynthesis by core-collapse supernovae in the Type Ia supernova time-delay scenario.The bulge sub-population compositions resemble the local thin and thick disks, but at higher [Fe/H], suggesting a radial [Fe/H] gradient of − $0.04]] > to − 0.05 dex/kpc for both the thin and thick disks. If the bulge formed through accretion of inner thin and thick disk stars, it appears that these stars retained vertical scale heights characteristic of their kinematic origin, resulting in the vertical [Fe/H] gradient and [α/Fe] trends seen today.

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