Erratum: Chemical Abundances of the Outer Halo Stars in the Milky Way: Table 2

ABSTRACT We investigate the intrinsic scatter in the chemical abundances of a sample of metal-poor ([Fe/H] < −2.5) Milky Way halo stars. We draw our sample from four historic surveys and focus our attention on the stellar Mg, Ca, Ni, and Fe abundances. Using these elements, we investigate the chemical enrichment of these metal-poor stars using a model of stochastic chemical enrichment. Assuming that these stars have been enriched by the first generation of massive metal-free stars, we consider the mass distribution of the enriching population alongside the stellar mixing and explosion energy of their supernovae. For our choice of stellar yields, our model suggests that the most metal-poor stars were enriched, on average, by $\hat{N}_{\star }=5^{+13}_{-3}~(1\sigma)$ Population III stars. This is comparable to the number of enriching stars inferred for the most metal-poor DLAs. Our analysis therefore suggests that some of the lowest mass structures at z ∼ 3 contain the chemical products from < 13(2σ) Population III enriched minihaloes. The inferred IMF is consistent with that of a Salpeter distribution and there is a preference towards ejecta from minimally mixed hypernovae. However, the estimated enrichment model is sensitive to small changes in the stellar sample. An offset of ∼ 0.1 dex in the [Mg/Ca] abundance is shown to be sensitive to the inferred number of enriching stars. We suggest that this method has the potential to constrain the multiplicity of the first generation of stars, but this will require: (1) a stellar sample whose systematic errors are well understood; and, (2) documented uncertainties associated with nucleosynthetic yields.

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Chemical abundances of field halo stars - Implications for the building blocks of the Milky Way

Proceedings of the International Astronomical Union ◽

10.1017/s1743921319007865 ◽

2019 ◽

Vol 14 (S351) ◽

pp. 24-33

Author(s):

Miho N. Ishigaki

Keyword(s):

Milky Way ◽

Building Blocks ◽

Chemical Information ◽

Wide Field ◽

Chemical Abundance ◽

Chemical Abundances ◽

Halo Stars ◽

Dimensional Phase Space ◽

Stellar Halo ◽

Detailed Chemical

AbstractI would like to review recent efforts of detailed chemical abundance measurements for field Milky Way halo stars. Thanks to the advent of wide-field spectroscopic surveys up to a several kpc from the Sun, large samples of field halo stars with detailed chemical measurements are continuously expanding. Combination of the chemical information and full six dimensional phase-space information is now recognized as a powerful tool to identify cosmological accretion events that have built a sizable fraction of the present-day stellar halo. Future observational prospects with wide-field spectroscopic surveys and theoretical prospects with supernova nucleosynthetic yields are also discussed.

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Contributions to the Galactic halo from in-situ, kicked-out, and accreted stars

Proceedings of the International Astronomical Union ◽

10.1017/s1743921315007140 ◽

2015 ◽

Vol 11 (S317) ◽

pp. 241-246

Author(s):

Allyson A. Sheffield ◽

Kathryn V. Johnston ◽

Katia Cunha ◽

Verne V. Smith ◽

Steven R. Majewski

Keyword(s):

Neutron Capture ◽

Milky Way ◽

Galactic Halo ◽

Galactic Disk ◽

High Resolution Spectroscopy ◽

Chemical Abundances ◽

Giant Stars ◽

Halo Stars ◽

Tentative Evidence

AbstractWe report chemical abundances for a sample of 66 M giants with high S/N high-resolution spectroscopy in the inner halo of the Milky Way. The program giant stars have radial velocities that vary significantly from those expected for stars moving on uniform circular orbits in the Galactic disk. Thus, based on kinematics, we expect a sample dominated by halo stars. Abundances are derived for α-elements and neutron capture elements. By analyzing the multi-dimensional abundance space, the formation site of the halo giants – in-situ or accreted – can be assessed. Of particular interest are a class of stars that form in-situ, deep in the Milky Way's gravitational potential well, but are “kicked out” of the disk into the halo due to a perturbation event. We find: (1) our sample is dominated by accreted stars and (2) tentative evidence of a small kicked-out population in our Milky Way halo sample.

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Chemical Abundances of Outer Halo Stars in the Milky Way

Publications of the Astronomical Society of Japan ◽

10.1093/pasj/62.1.143 ◽

2010 ◽

Vol 62 (1) ◽

pp. 143-178 ◽

Cited By ~ 35

Author(s):

Miho Ishigaki ◽

Masashi Chiba ◽

Wako Aoki

Keyword(s):

Milky Way ◽

Chemical Abundances ◽

Halo Stars

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The messy merger of a large satellite and a Milky Way-like galaxy

Astronomy and Astrophysics ◽

10.1051/0004-6361/202038652 ◽

2020 ◽

Vol 642 ◽

pp. L18 ◽

Cited By ~ 1

Author(s):

Helmer H. Koppelman ◽

Roy O. Y. Bos ◽

Amina Helmi

Keyword(s):

Milky Way ◽

Space Structure ◽

Disc Galaxy ◽

Chemical Abundances ◽

Phase Space Structure ◽

Halo Stars ◽

Wide Range ◽

Merger Event ◽

Separate System ◽

Hydrodynamical Simulations

Aims. About 10 billion years ago the Milky Way merged with a massive satellite, Gaia-Enceladus. To gain insight into the properties of its debris we analyse in detail a suite of simulations that includes an experiment that produces a good match to the kinematics of nearby halo stars inferred from Gaia data. Methods. We compare the kinematic distributions of stellar particles in the simulations and study the distribution of debris in orbital angular momentum, eccentricity, and energy, and its relation to the mass loss history of the simulated satellite. Results. We confirm that Gaia-Enceladus probably fell in on a retrograde, 30° inclination orbit. We find that while 75% of the debris in our preferred simulation has high eccentricity (> 0.8), roughly 9% has eccentricity lower than 0.6. Star particles lost early have large retrograde motions, and a subset of these have low eccentricity. Such stars would be expected to have lower metallicities as they stem from the outskirts of the satellite, and hence naively they could be confused with debris associated with a separate system. These considerations seem to apply to some of the stars from the postulated Sequoia galaxy. Conclusions. When a massive disc galaxy undergoes a merger event, it leaves behind debris with a complex phase-space structure, a wide range of orbital properties, and a range of chemical abundances. Observationally, this results in substructures with very different properties, which can be misinterpreted as implying independent progeny. Detailed chemical abundances of large samples of stars and tailored hydrodynamical simulations are critical to resolving such conundrums.

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The mass of the Milky Way out to 100 kpc using halo stars

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3984 ◽

2020 ◽

Author(s):

Alis J Deason ◽

Denis Erkal ◽

Vasily Belokurov ◽

Azadeh Fattahi ◽

Facundo A Gómez ◽

...

Keyword(s):

Distribution Function ◽

Mass Concentration ◽

Milky Way ◽

Function Analysis ◽

Large Magellanic Cloud ◽

Systematic Bias ◽

Cosmological Simulations ◽

Halo Stars ◽

Systematic Effects ◽

Mass Estimate

Abstract We use a distribution function analysis to estimate the mass of the Milky Way out to 100 kpc using a large sample of halo stars. These stars are compiled from the literature, and the vast majority ($\sim \! 98\%$) have 6D phase-space information. We pay particular attention to systematic effects, such as the dynamical influence of the Large Magellanic Cloud (LMC), and the effect of unrelaxed substructure. The LMC biases the (pre-LMC infall) halo mass estimates towards higher values, while realistic stellar halos from cosmological simulations tend to underestimate the true halo mass. After applying our method to the Milky Way data we find a mass within 100 kpc of M( < 100kpc) = 6.07 ± 0.29(stat.) ± 1.21(sys.) × 1011M⊙. For this estimate, we have approximately corrected for the reflex motion induced by the LMC using the Erkal et al. model, which assumes a rigid potential for the LMC and MW. Furthermore, stars that likely belong to the Sagittarius stream are removed, and we include a 5% systematic bias, and a 20% systematic uncertainty based on our tests with cosmological simulations. Assuming the mass-concentration relation for Navarro-Frenk-White haloes, our mass estimate favours a total (pre-LMC infall) Milky Way mass of M200c = 1.01 ± 0.24 × 1012M⊙, or (post-LMC infall) mass of M200c = 1.16 ± 0.24 × 1012 M⊙ when a 1.5 × 1011M⊙ mass of a rigid LMC is included.

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Structure and dynamics of the Milky Way disk as revealed from the radial velocity distributions of APOGEE red clump stars

Proceedings of the International Astronomical Union ◽

10.1017/s174392131601173x ◽

2016 ◽

Vol 11 (S321) ◽

pp. 50-50

Author(s):

Daisuke Toyouchi ◽

Masashi Chiba

Keyword(s):

Near Infrared ◽

Milky Way ◽

Radial Velocities ◽

Galactocentric Distance ◽

Chemical Abundances ◽

Structure And Dynamics ◽

Evolution Experiment ◽

Dynamical Properties ◽

Red Clump ◽

Independent Work

AbstractWe investigate the structure and dynamics of the Milky Way (MW) disk stars based on the analysis of the Apache Point Observatory Galactic Evolution Experiment (APOGEE) data, to infer the past evolution histories of the MW disk component(s) possibly affected by radial migration and/or satellite accretions. APOGEE is the first near-infrared spectroscopic survey for a large number of the MW disk stars, providing their radial velocities and chemical abundances without significant dust extinction effects. We here adopt red-clump (RC) stars (Bovy et al. 2014), for which the distances from the Sun are determined precisely, and analyze their radial velocities and chemical abundances in the MW disk regions covering from the Galactocentric distance, R, of 5 kpc to 14 kpc. We investigate their dynamical properties, such as mean rotational velocities, 〈Vφ〉 and velocity dispersions, as a function of R, based on the MCMC Bayesian method. We find that at all radii, the dynamics of alpha-poor stars, which are candidates of young disk stars, is much different from that of alpha-rich stars, which are candidates of old disk stars. We find that our Jeans analysis for our sample stars reveals characteristic spatial and dynamical properties of the MW disk, which are generally in agreement with the recent independent work by Bovy et al. (2015) but with a different method from ours.

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The U/Th production ratio and the age of the Milky Way from meteorites and Galactic halo stars

Nature ◽

10.1038/nature03645 ◽

2005 ◽

Vol 435 (7046) ◽

pp. 1203-1205 ◽

Cited By ~ 63

Author(s):

Nicolas Dauphas

Keyword(s):

Milky Way ◽

Galactic Halo ◽

Halo Stars ◽

Production Ratio

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Phase‐Space Distributions of Chemical Abundances in Milky Way–Type Galaxy Halos

The Astrophysical Journal ◽

10.1086/505131 ◽

2006 ◽

Vol 646 (2) ◽

pp. 886-898 ◽

Cited By ~ 83

Author(s):

Andreea S. Font ◽

Kathryn V. Johnston ◽

James S. Bullock ◽

Brant E. Robertson

Keyword(s):

Phase Space ◽

Milky Way ◽

Chemical Abundances ◽

Galaxy Halos

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Chemical Abundances of Seven Outer Halo M31 Globular Clusters from the Pan-Andromeda Archaeological Survey

Proceedings of the International Astronomical Union ◽

10.1017/s1743921316011200 ◽

2016 ◽

Vol 11 (S321) ◽

pp. 10-12

Author(s):

Charli M. Sakari

Keyword(s):

Globular Clusters ◽

Milky Way ◽

Dwarf Galaxy ◽

Large Magellanic Cloud ◽

Archaeological Survey ◽

Chemical Abundances ◽

Light Spectra ◽

Sigma Level ◽

Stellar Streams ◽

Detailed Chemical

AbstractObservations of stellar streams in M31’s outer halo suggest that M31 is actively accreting several dwarf galaxies and their globular clusters (GCs). Detailed abundances can chemically link clusters to their birth environments, establishing whether or not a GC has been accreted from a satellite dwarf galaxy. This talk presents the detailed chemical abundances of seven M31 outer halo GCs (with projected distances from M31 greater than 30 kpc), as derived from high-resolution integrated-light spectra taken with the Hobby Eberly Telescope. Five of these clusters were recently discovered in the Pan-Andromeda Archaeological Survey (PAndAS)—this talk presents the first determinations of integrated Fe, Na, Mg, Ca, Ti, Ni, Ba, and Eu abundances for these clusters. Four of the target clusters (PA06, PA53, PA54, and PA56) are metal-poor ([Fe/H] < -1.5), α-enhanced (though they are possibly less alpha-enhanced than Milky Way stars at the 1 sigma level), and show signs of star-to-star Na and Mg variations. The other three GCs (H10, H23, and PA17) are more metal-rich, with metallicities ranging from [Fe/H] = -1.4 to -0.9. While H23 is chemically similar to Milky Way field stars, Milky Way GCs, and other M31 clusters, H10 and PA17 have moderately-low [Ca/Fe], compared to Milky Way field stars and clusters. Additionally, PA17’s high [Mg/Ca] and [Ba/Eu] ratios are distinct from Milky Way stars, and are in better agreement with the stars and clusters in the Large Magellanic Cloud (LMC). None of the clusters studied here can be conclusively linked to any of the identified streams from PAndAS; however, based on their locations, kinematics, metallicities, and detailed abundances, the most metal-rich PAndAS clusters H23 and PA17 may be associated with the progenitor of the Giant Stellar Stream, H10 may be associated with the SW Cloud, and PA53 and PA56 may be associated with the Eastern Cloud.

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