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

Timothy C. Beers*, John E. Norris, Vinicius M. Placco, Young Sun Lee, Silvia Rossi, Daniela Carollo, Thomas Masseron

*Corresponding author for this work

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    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 & 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 (Teff, 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 a 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.

    Original languageEnglish
    Article number58
    Pages (from-to)1-19
    Number of pages19
    JournalAstrophysical Journal
    Issue number1
    Publication statusPublished - 10 Oct 2014

    Bibliographical note

    Copyright 2014 The American Astronomical Society. First published in The Astrophysical Journal, 794(1), 58, 2014. The original publication is available at http://www.doi.org/10.1088/0004-637X/794/1/58, published by IOP Publishing. Version archived for private and non-commercial use with the permission of the author/s and according to publisher conditions. For further rights please contact the publisher.


    • Galaxy: kinematics and dynamics
    • Galaxy: stellar content
    • Galaxy: structure
    • stars: abundances
    • stars: Population II


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