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Title: Population studies. XIII. A new analysis of the Bidelman-Macconnell 'weak-metal' stars - confirmation of metal-poor stars in the thick disk of the galaxy

A new set of very high signal-to-noise (S/N > 100/1), medium-resolution (R ∼ 3000) optical spectra have been obtained for 302 of the candidate 'weak-metal' stars selected by Bidelman and MacConnell. We use these data to calibrate the recently developed generalization of the Sloan Extension for Galactic Exploration and Understanding and Exploration (SEGUE) Stellar Parameter Pipeline, and obtain estimates of the atmospheric parameters (T {sub eff}, log g, and [Fe/H]) for these non-Sloan Digital Sky Survey/SEGUE data; we also obtain estimates of [C/Fe]. The new abundance measurements are shown to be consistent with available high-resolution spectroscopic determinations, and represent a substantial improvement over the accuracies obtained from the previous photometric estimates reported in Paper I of this series. The apparent offset in the photometric abundances of the giants in this sample noted by several authors is confirmed by our new spectroscopy; no such effect is found for the dwarfs. The presence of a metal-weak thick-disk (MWTD) population is clearly supported by these new abundance data. Some 25% of the stars with metallicities –1.8 < [Fe/H] ≤–0.8 exhibit orbital eccentricities e < 0.4, yet are clearly separated from members of the inner-halo population with similar metallicities by their location in amore » Lindblad energy versus angular momentum diagram. A comparison is made with recent results for a similar-size sample of Radial Velocity Experiment stars from Ruchti et al. We conclude, based on both of these samples, that the MWTD is real, and must be accounted for in discussions of the formation and evolution of the disk system of the Milky Way.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [6] ;  [7]
  1. Department of Physics and JINA Center for the Evolution of the Elements, University of Notre Dame, Notre Dame, IN 46556 (United States)
  2. Research School of Astronomy and Astrophysics, The Australian National University, Mount Stromlo Observatory, Cotter Road, Weston, ACT 2611 (Australia)
  3. Gemini Observatory, Hilo, HI 96720 (United States)
  4. Department of Astronomy and Space Science, Chungnam National University, Daejeon 305-764 (Korea, Republic of)
  5. Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Departamento de Astronomia, Universidade de São Paulo, Rua do Matão 1226, 05508-900 São Paulo (Brazil)
  6. Department of Physics and Astronomy, Astronomy, Astrophysics and Astrophotonic Research Center, Macquarie University, North Ryde 2019, NSW (Australia)
  7. Institute of Astronomy, University of Cambridge, CB3 0HA (United Kingdom)
Publication Date:
OSTI Identifier:
22370456
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 794; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABUNDANCE; ACCURACY; ANGULAR MOMENTUM; COMPARATIVE EVALUATIONS; EXPLORATION; METALLICITY; METALS; MILKY WAY; NOISE; RADIAL VELOCITY; RESOLUTION; SKY; SPECTRA; SPECTROSCOPY; STARS