A Comparison of the Chemical Evolutionary Histories of the Galactic Thin Disk and Thick Disk Stellar Populations

Brewer, Mary-Margaret; Carney, Bruce W.

doi:10.1086/498110

Cited by 68 publications

(78 citation statements)

References 82 publications

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“…Scandium Figure 3a shows the abundance result for Sc; it is evident that the [Sc/Fe] Our results are consistent with previous works, including Prochaska et al (2000), Nissen et al (2000), Allende Prieto et al (2004), Reddy et al (2006), Brewer & Carney (2006), Adibekyan et al (2012), and Ishigaki et al (2013). It is worth noting that the sample studied in Ishigaki et al (2013) reaches [Fe/H] ≈ −3 with solar [Sc/Fe], confirming what we see from the few metal-poor stars analyzed in this work.…”

Section: General Abundance Trendssupporting

confidence: 91%

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The origin and evolution of the odd-Z iron-peak elements Sc, V, Mn, and Co in the Milky Way stellar disk

Battistini

Bensby

2015

A&A

140

213

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Context. Elements heavier than Li are produced in the interiors of stars. However, for many elements the exact production sites and the timescales on which they are dispersed into the interstellar medium are unknown. Having a clear picture on the origins of the elements is important for our ability to trace and understand the formation and chemical evolution of the Milky Way and its stellar populations. Aims. The aim of this study is to investigate the origin and evolution of Sc, V, Mn, and Co for a homogeneous and statistically significant sample of stars probing the different populations of the Milky Way, in particular the thin and thick disks. Methods. Using high-resolution spectra obtained with the MIKE, FEROS, SOFIN, FIES, UVES, and HARPS spectrographs, we determine Sc, V, Mn, and Co abundances for a large sample of F and G dwarfs in the solar neighborhood. The method is based on spectral synthesis and using one-dimensional, plane-parallel, local thermodynamic equilibrium (LTE) model stellar atmospheres calculated with the MARCS 2012 code. The non-LTE (NLTE) corrections from the literature were applied to Mn and Co. Results. We find that the abundance trends derived for Sc (594 stars

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Section: General Abundance Trendssupporting

confidence: 91%

“…In Figs. 4c and d, the LTE case shows that the trends for the young and old populations are similar and difficult to distinguish, as also pointed out in Brewer & Carney (2006). In the NLTE case, a difference between old and young population seems to be present in the metallicity range −0.6 [Fe/H] −0.1.…”

Section: Thin and Thick Disk Trendsmentioning

confidence: 56%

The origin and evolution of the odd-Z iron-peak elements Sc, V, Mn, and Co in the Milky Way stellar disk

Battistini

Bensby

2015

A&A

140

213

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“…We found a significant fraction of these stars (∼40%) to be most consistent with the thick disk. The abundances of these metal-poor thick-disk stars had high [α/Fe] ratios, consistent with rapid star formation, which agrees with previous studies of much smaller samples of metal-poor thick-disk stars (Fulbright 2002;Bensby et al 2003;Brewer & Carney 2006;Reddy et al 2006;Reddy & Lambert 2008;AlvesBrito et al 2010). Further, we found that the [α/Fe] ratios were indistinguishable from those of the halo, indicating that the halo and the thick disk shared a similar massive-star IMF and similar efficient mixing of enriched material into the ISM.…”

Section: Introductionsupporting

confidence: 90%

Observational Properties of the Metal-Poor Thick Disk of the Milky Way and Insights Into Its Origins

Ruchti

Fulbright

Wyse

et al. 2011

ApJ

101

108

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We have undertaken the study of the elemental abundances and kinematic properties of a metal-poor sample of candidate thick-disk stars selected from the Radial Velocity Experiment spectroscopic survey of bright stars to differentiate among the present scenarios of the formation of the thick disk. In this paper, we report on a sample of 214 red giant branch, 31 red clump/horizontal branch, and 74 main-sequence/sub-giant branch metalpoor stars, which serves to augment our previous sample of only giant stars. We find that the thick disk [α/Fe] ratios are enhanced and have little variation (<0.1 dex), in agreement with our previous study. The augmented sample further allows, for the first time, investigation of the gradients in the metal-poor thick disk. For stars with [Fe/H] < −1.2, the thick disk shows very small gradients, <0.03 ± 0.02 dex kpc −1 , in α-enhancement, while we find a +0.01 ± 0.04 dex kpc −1 radial gradient and a −0.09 ± 0.05 dex kpc −1 vertical gradient in iron abundance. In addition, we show that the peak of the distribution of orbital eccentricities for our sample agrees better with models in which the stars that comprise the thick disk were formed primarily in the Galaxy, with direct accretion of stars contributing little. Our results thus disfavor direct accretion of stars from dwarf galaxies into the thick disk as a major contributor to the thick-disk population, but cannot discriminate between alternative models for the thick disk, such as those that invoke high-redshift (gas-rich) mergers, heating of a pre-existing thin stellar disk by a minor merger, or efficient radial migration of stars.

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“…A number of studies have claimed ∼0.2 dex [Sc/Fe] enhancements in metal-poor stars of the MW halo and thick and thin disks (e.g., Zhao & Magain 1990;Nissen et al 2000;Carretta et al 2002;Cohen et al 2004;Brewer & Carney 2006;Reddy et al 2006). However, it has been pointed-out that errors in log g f values and/or the treatment of hyperfine structure (e.g., Gratton & Sneden 1991;Prochaska & McWilliam 2000) Error bars account for random and systematic uncertainties.…”

Section: Scandium: No Evidence For Population III Enrichmentmentioning

confidence: 99%

Metal-poor stars towards the Galactic bulge: A population potpourri

Koch

McWilliam

Preston

et al. 2016

A&A

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We present a comprehensive chemical abundance analysis of five red giants and two horizontal branch (HB) stars towards the southern edge of the Galactic bulge, at (l, b) ∼ (0 • ,−11 • ). Based on high-resolution spectroscopy obtained with the Magellan/MIKE spectrograph, we derived up to 23 chemical element abundances and identify a mixed bag of stars, representing various populations in the central regions of the Galaxy. Although cosmological simulations predict that the inner Galaxy was host to the first stars in the Universe, we see no chemical evidence of the ensuing massive supernova explosions: all of our targets exhibit halo-like, solar [Sc/Fe] ratios, which is in contrast to the low values predicted from Population III nucleosynthesis. One of the targets is a CEMP-s star at [Fe/H] = −2.52 dex, and another target is a moderately metal-poor ([Fe/H] = −1.53 dex) CH star with strong enrichment in s-process elements (e.g., [Ba/Fe] = 1.35). These individuals provide the first contenders of these classes of stars towards the bulge. Four of the carbon-normal stars exhibit abundance patterns reminiscent of halo star across a metallicity range spanning −2.0 to −2.6 dex, i.e., enhanced α-elements and solar Fe-peak and neutron-capture elements, and the remaining one is a regular metal-rich bulge giant. The position, distance, and radial velocity of one of the metal-poor HB stars coincides with simulations of the old trailing arm of the disrupted Sagittarius dwarf galaxy. While their highly uncertain proper motions prohibit a clear kinematic separation, the stars' chemical abundances and distances suggest that these metal-poor candidates, albeit located towards the bulge, are not of the bulge, but rather inner halo stars on orbits that make them pass through the central regions. Thus, we caution similar claims of detections of metal-poor stars as true habitants of the bulge.

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A Comparison of the Chemical Evolutionary Histories of the Galactic Thin Disk and Thick Disk Stellar Populations

Cited by 68 publications

References 82 publications

The origin and evolution of the odd-Z iron-peak elements Sc, V, Mn, and Co in the Milky Way stellar disk

The origin and evolution of the odd-Z iron-peak elements Sc, V, Mn, and Co in the Milky Way stellar disk

Observational Properties of the Metal-Poor Thick Disk of the Milky Way and Insights Into Its Origins

Metal-poor stars towards the Galactic bulge: A population potpourri

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