A Survey of Proper Motion Stars. XIII. The Halo Population

Carney, Bruce W.; Laird, John B.; Latham, David W.; Aguilar, L. A.

doi:10.1086/118042

Cited by 165 publications

(212 citation statements)

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“…Carney et al showed that their "" high halo ÏÏ sample, with S[Fe/H]T \ [2.04 and kpc, exhibited a net retrograde rota-Z max º 5 tion km s~1), whereas their "" low halo ÏÏ (SV Õ T \ [45^22 sample at kpc exhibited a net prograde rotation Z max ¹ 2 ranging from km s~1 to 44 km s~1, depending SV Õ T \ 12 on the speciÐc criteria chosen to avoid stars of the disk component. Figure 11a reproduces the original data of Carney et al (1996), for stars with [Fe/H] ¹ [1.5. Since, in their estimates of Carney et al adopted a di †erent Galactic Z max , potential than ours, we have also redetermined for Z max their sample with the same potential described in°3, and show the results in this same Ðgure.…”

Section: Global Dynamics and Structure Of The Halomentioning

confidence: 71%

“…SZ suggested that in its earliest epochs the halo component of the Galaxy may have experienced prolonged, chaotic accretion of subgalactic fragments. More recent studies of halo Ðeld stars also provide evidence that may support the SZ picture, including a possible age spread among halo subdwarfs (e.g., Schuster & Nissen 1989 ;Carney et al 1996), a gradient in the inferred ages of Ðeld horizontal-branch (FHB) stars and RR Lyrae variables, in the sense that the outer halo FHB stars and RR Lyrae variables appear several gigayears younger than those of the inner halo (Preston, Shectman, & Beers 1991 ;Lee & Carney 1999), a report of the apparent clustering of FHB stars in the halo (Doinidis & Beers 1989), possible kinematic substructure in the halo (e.g., Doinidis & Beers 1989 ;Majewski, Munn, & Hawley 1994 ;, and distinct changes in the kinematics of the Ðeld populations as one moves from the inner to outer halo (e.g., Majewski 1992 ;Carney et al 1996 ;Sommer-Larsen et al 1997).…”

Section: Introductionmentioning

confidence: 92%

“…This result was taken to indicate the possible existence of a dynamically "" hot ÏÏ protodisk population at low abundances. Carney et al (1996) disputed this result, as their analysis of a di †erent set of high proper-motion stars indicated that the disk component is not dynamically hot, at least when membership is conÐned to the stars orbiting exclusively within the inner part of the Galaxy, R ¹ 14 kpc. Figure 2c shows no evidence for an increase of at low p W abundances.…”

Section: Of Cy)mentioning

confidence: 99%

“…For comparison, the dashed line denotes the result of Carney et al (1996) for their high proper-motion sample. There is a clear di †erence from our resultsÈthe use of a kinematically selected sample overestimates the average orbital eccentricities at a given [Fe/H] by an amount up to 0.2.…”

Section: Orbital Properties Of the Metal-poor Starsmentioning

confidence: 99%

“…In order to assess which picture, ELS or SZ (or both, e.g., Norris 1994 ;Freeman 1996 ;Carney et al 1996), more correctly describes the early history of the Galaxy, we require a large and reliable set of data for halo-population objects chosen with criteria that do not unduly inÑuence the subsequent analysis. As we show, the analysis of stars chosen with a kinematic selection bias can be particularly troublesome.…”

Section: Introductionmentioning

confidence: 99%

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Kinematics of Metal-poor Stars in the Galaxy. III. Formation of the Stellar Halo and Thick Disk as Revealed from a Large Sample of Nonkinematically Selected Stars

Chiba

Beers

2000

The Astronomical Journal

645

108

716

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We present a detailed analysis of the space motions of 1203 solar-neighborhood stars with metal abundances [Fe/H] ¹ [0.6, on the basis of a catalog, of metal-poor stars selected without kinematic bias recently revised and supplemented by Beers et al. This sample, having available proper motions, radial velocities, and distance estimates for stars with a wide range of metal abundances, is by far the largest such catalog to be assembled to date. We show that the stars in our sample with [Fe/H] ¹[2.2, which likely represent a "" pure ÏÏ halo component, are characterized by a radially elongated velocity ellipsoid 106^9, 94^8) km s~1 and small prograde rotation to 50 km, consistent with previous analysis of this sample by Beers and Sommer-Larsen based on radial velocity information alone. In contrast to the previous analysis, we Ðnd a decrease in with increasing SV Õ T distance from the Galactic plane for stars that are likely to be members of the halo population km s~1 kpc~1), which may represent the signature of a dissipatively formedUnlike essentially all previous kinematically selected catalogs, the metal-poor stars in our sample exhibit a diverse distribution of orbital eccentricities, e, with no apparent correlation between [Fe/H] and e. This demonstrates, clearly and convincingly, that the evidence o †ered in 1962 by Eggen, Lynden-Bell, & Sandage for a rapid collapse of the Galaxy, an apparent correlation between the orbital eccentricity of halo stars with metallicity, is basically the result of their proper-motion selection bias. However, even in our nonkinematically selected sample, we have identiÐed a small concentration of high-e stars at [Fe/H] D [1.7, which may originate, in part, from infalling gas during the early formation of the Galaxy. We Ðnd no evidence for an additional thick disk component for stellar abundances We also analyze the global kinematics of the stars constituting the halo component of the Galaxy. The outer part of the halo, which we take to be represented by local stars on orbits reaching more than 5 kpc from the Galactic plane, exhibits no systematic rotation. In particular, we show that previous suggestions of the presence of a "" counter-rotating high halo ÏÏ are not supported by our analysis. The density distribution of the outer halo is nearly spherical and exhibits a power-law proÐle that is accurately described as o P R~3.55B0.13. The inner part of the halo is characterized by a prograde rotation and a highly Ñattened density distribution. We Ðnd no distinct boundary between the inner and outer halo. We conÐrm the clumping in angular-momentum phase space of a small number of local metalpoor stars noted in 1999 by Helmi et al. We also identify an additional elongated feature in angularmomentum phase space extending from the clump to regions with high azimuthal rotation. The number of members in the detected clump is not signiÐcantly increased from that reported by Helmi et al., even though the total number of the sample stars we consider is almost triple that of the prev...

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Section: Global Dynamics and Structure Of The Halomentioning

confidence: 71%

Section: Introductionmentioning

confidence: 92%

Section: Of Cy)mentioning

confidence: 99%

Section: Orbital Properties Of the Metal-poor Starsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Kinematics of Metal-poor Stars in the Galaxy. III. Formation of the Stellar Halo and Thick Disk as Revealed from a Large Sample of Nonkinematically Selected Stars

Chiba

Beers

2000

The Astronomical Journal

645

108

716

View full text Add to dashboard Cite

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Spectroscopic and dynamic orbital analyses of metal‐poor and high proper‐motion stars: I. HD 8724 and HD 195633

Marışmak,

Şahin,

Güney

et al. 2024

Astron Nachr

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In this study, spectral, age, kinematic, and orbital dynamical analyses were conducted on metal‐poor and high proper‐motion (HPM) stars, HD 8724 and HD 195633, selected from the Solar neighborhood. This analysis combines detailed abundance measurements, kinematics, and orbital dynamics to determine their origin. Standard 1D local thermodynamic equilibrium analysis provides a fresh determination of the atmospheric parameters: Teff = 4700 ± 115 K, log g = 1.65 ± 0.32 cgs, [Fe/H] = −1.59 ± 0.04 dex, and a microturbulent velocity 1.58 ± 0.50 km s−1 for HD 8724 and Teff = 6100 ± 205 K, log g = 3.95 ± 0.35 cgs, [Fe/H] = −0.52 ± 0.05 dex, and 1.26 ± 0.50 km s−1 for HD 195633. The ages were estimated using a Bayesian approach (12.25 Gyr for HD 8724 and 8.15 Gyr for HD 195633). The escape scenarios of these stars from 170 candidate globular clusters (GCs) in the Galaxy were also investigated because of their chemical and physical differences (HPM and metal‐poor nature). Accordingly, the calculated probability of encounter (59%) for HD 8724 at a distance of five tidal radius suggests that star HD 8724 may have escaped from NGC 5139 ( Cen), supported by its highly flattened orbit and may belong to a subpopulation of this GC. Conversely, HD 195633's kinematics, age, and metal abundances point toward an escape from the bulge GC NGC 6356.

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Metal-Poor Halo Stars as Tracers of ISM Mixing Processes During Halo Formation

Argast

Samland

Gerhard

et al.

Eso Astrophysics Symposia

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Abstract. We introduce a stochastic halo formation model to compute the early chemical enrichment of the interstellar medium (ISM) of the halo. Contrary to 1-zone chemical evolution models, we are able to resolve local inhomogeneities in the ISM caused by single core-collapse supernovae. These inhomogeneities lead to different element abundance patterns in very metal-poor stars, which can be seen as scatter in the abundances of halo stars with metallicities [Fe/H] < 2.0.The early chemical evolution of the halo proceeds in different enrichment phases: At [Fe/H] < −3.0, the halo ISM is unmixed and dominated by local inhomogeneities caused by individual core-collapse supernova (SN) events. For metallicities [Fe/H] > −2.0 the halo ISM is well mixed, showing an element abundance pattern integrated over the initial mass function. In the range −3.0 < [Fe/H] < −2.0 a continuous transition from the unmixed to the well mixed ISM occurs.For some elements (Si, Ca, Eu), the scatter in the elementto-iron ratio [El/Fe] of metal-poor halo stars can be reproduced. Stellar yields of other elements predict a scatter which, compared to the observations, is too large (O, Mg) or too small (Ni). Cr and Mn show a decreasing trend for lower metallicities, which can not be explained by metallicity independent yields, provided that the mixing of the ejecta with the interstellar medium does not depend on progenitor mass. This demonstrates the need for revised, self-consistent SN yields.Finally, we discuss the metallicity distribution in the model. Compared to the 28 very metal-poor stars observed with metallicities in the range −4.0 < [Fe/H] < −3.0, no star is known with confirmed metallicity [Fe/H] < −4.0, while our model predicts 5 ± 2 stars with [Fe/H] < −4.0. These should be present if the halo ISM started at primordial metallicities and no pre-enrichment by population III stars occurred.

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A Survey of Proper Motion Stars. XIII. The Halo Population

Cited by 165 publications

References 0 publications

Kinematics of Metal-poor Stars in the Galaxy. III. Formation of the Stellar Halo and Thick Disk as Revealed from a Large Sample of Nonkinematically Selected Stars

Kinematics of Metal-poor Stars in the Galaxy. III. Formation of the Stellar Halo and Thick Disk as Revealed from a Large Sample of Nonkinematically Selected Stars

Spectroscopic and dynamic orbital analyses of metal‐poor and high proper‐motion stars: I. HD 8724 and HD 195633

Metal-Poor Halo Stars as Tracers of ISM Mixing Processes During Halo Formation

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