Population studies. I - The Bidelman-MacConnell 'weak-metal' stars

Norris, John E.; Bessell, M. S.; Pickles, Andrew

doi:10.1086/191049

Cited by 165 publications

(150 citation statements)

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“…However, most of them were based on low-or mediumresolution spectroscopy (e.g., Bond 1980;Norris, Bessell, & Pickles 1985). We choose to compare our measurements with only the results of high-dispersion spectroscopy from recent studies.…”

Section: Measurements Of Radial Velocitiesmentioning

confidence: 99%

Spectroscopic Studies of Extremely Metal‐Poor Stars with the Subaru High Dispersion Spectrograph. I. Observational Data

Honda

Aoki

Ando

et al. 2004

ASTROPHYS J SUPPL S

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We have obtained high-resolution (R ' 50; 000 or 90,000), high-quality (S= N k 100) spectra of 22 very metalpoor stars ([Fe/H P À 2:5) with the High Dispersion Spectrograph fabricated for the 8.2 m Subaru Telescope. The spectra cover the wavelength range from 3500 to 5100 8; equivalent widths are measured for isolated lines of numerous elemental species, including the -elements, the iron-peak elements, and the light and heavy neutron-capture elements. Errors in the measurements and comparisons with previous studies are discussed. These data will be used to perform detailed abundance analyses in the following papers of this series. Radial velocities are also reported and are compared with previous studies. At least one moderately r-process-enhanced metal-poor star, HD 186478, exhibits evidence of a small-amplitude radial velocity variation, confirming the binary status noted previously. During the course of this initial program, we have discovered a new moderately r-process-enhanced, very metal-poor star, CS 30306À132 ([Fe/H ¼ À2:4; [Eu/Fe ¼ þ0:85), which is discussed in detail in the companion paper.

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Section: Measurements Of Radial Velocitiesmentioning

confidence: 99%

Spectroscopic Studies of Extremely Metal‐Poor Stars with the Subaru High Dispersion Spectrograph. I. Observational Data

Honda

Aoki

Ando

et al. 2004

ASTROPHYS J SUPPL S

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“…Focusing on the lack of metal-poor stars with low-eccentricity orbits in their (proper-motion selected) sample, ELS argued that the Galaxy must have undergone a rapid collapse, then formed a rotationally supported disk. Although criticism of the ELS model has been levied because of the potential inÑu-ence of their kinematic selection bias, especially the extent to which this might alter the derived collapse timescale of the early Galaxy (Yoshii & Saio 1979 ;Norris, Bessell, & Pickles 1985 ;Norris 1986 ;Norris & Ryan 1991 ;Beers & Sommer-Larsen 1995, hereafter BSL ;Chiba & Yoshii 1998, hereafter CY), the ELS collapse picture has long been inÑu-ential for studies of disk galaxies like our own and for elliptical galaxies as well (e.g., Larson 1974 ;van Albada 1982).…”

Section: Introductionmentioning

confidence: 99%

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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“…However, despite some specific attempts to characterise the wings of the distributions (e.g. Norris et al 1985;Chiba & Beers 2000;Carollo et al 2010;Ruchti et al 2011;Kordopatis et al 2013bKordopatis et al , 2015, the overlap in kinematics and metallicity for the discs implies that the shape and extent of their distribution functions still remain uncertain. The best discriminant parameter seems to be the stellar age, as thick-disc stars are consistently older than 9 Gyr (e.g.…”

Section: Introductionmentioning

confidence: 99%

TheGaia-ESO Survey: characterisation of the [α/Fe] sequences in the Milky Way discs

Kordopatis

Wyse

Gilmore

et al. 2015

A&A

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Context. High-resolution spectroscopic surveys of stars indicate that the Milky Way thin and thick discs follow different paths in the chemical space defined by [α/Fe] vs. [Fe/H], possibly suggesting different formation mechanisms for each of these structures. Aims. We investigate, using the Gaia-ESO Survey internal Data-Release 2, the properties of the double sequence of the Milky Way discs, which are defined chemically as the high-α and low-α populations. We discuss their compatibility with discs defined by other means, such as metallicity, kinematics, or positions. Methods. This investigation uses two different approaches: in velocity space, for stars located in the extended solar neighbourhood; and, in chemical space, for stars at different ranges of Galactocentric radii and heights from the Galactic mid-plane. The separation we find in velocity space allows us to investigate, using a novel approach, the extent of metallicity of each of the two chemical sequences, without making any assumption about the shape of their metallicity distribution functions. Then, using the separation in chemical space, adopting the magnesium abundance as a tracer of the α-elements, we characterise the spatial variation of the slopes of the [α/Fe]−[Fe/H] sequences for the thick and thin discs and the way in which the relative proportions of the two discs change across the Galaxy. Results. We find that the thick disc, defined as the stars tracing the high-α sequence, extends up to super-solar metallicities ([Fe/H] ≈ +0.2 dex), and the thin disc, defined as the stars tracing the low-α sequence, extends at least down to [Fe/H] ≈ −0.8 dex, with hints pointing towards even lower values. Radial and vertical gradients in α-abundances are found for the thin disc, with mild spatial variations in its [α/Fe]−[Fe/H] paths, whereas for the thick disc we do not detect any spatial variations of this kind. This is in agreement with results obtained recently from other high-resolution spectroscopic surveys. Conclusions. The small variations in the spatial [α/Fe]−[Fe/H] paths of the thin disc do not allow us to distinguish between formation models of this structure. On the other hand, the lack of radial gradients and [α/Fe]−[Fe/H] variations for the thick disc indicate that the mechanism responsible for the mixing of metals in the young Galaxy (e.g. radial stellar migration or turbulent gaseous disc) was more efficient before the (present) thin disc started forming.

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Population studies. I - The Bidelman-MacConnell 'weak-metal' stars

Cited by 165 publications

References 0 publications

Spectroscopic Studies of Extremely Metal‐Poor Stars with the Subaru High Dispersion Spectrograph. I. Observational Data

Spectroscopic Studies of Extremely Metal‐Poor Stars with the Subaru High Dispersion Spectrograph. I. Observational Data

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

TheGaia-ESO Survey: characterisation of the [α/Fe] sequences in the Milky Way discs

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