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    Oxygen Abundances In Nearby FGK Stars And The Galactic Chemical Evolution Of The Local Disk And Halo

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    Date
    2013-02
    Author
    Ramirez, Ivan
    Prieto, Carlos Allende
    Lambert, David L.
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    Abstract
    Atmospheric parameters and oxygen abundances of 825 nearby FGK stars are derived using high-quality spectra and a non-local thermodynamic equilibrium analysis of the 777 nm O I triplet lines. We assign a kinematic probability for the stars to be thin-disk (P-1), thick-disk (P-2), and halo (P-3) members. We confirm previous findings of enhanced [O/Fe] in thick-disk (P-2 > 0.5) relative to thin-disk (P-1 > 0.5) stars with [Fe/H] less than or similar to -0.2, as well as a "knee" that connects the mean [O/Fe]-[Fe/H] trend of thick-disk stars with that of thin-disk members at [Fe/H] greater than or similar to -0.2. Nevertheless, we find that the kinematic membership criterion fails at separating perfectly the stars in the [O/Fe]-[Fe/H] plane, even when a very restrictive kinematic separation is employed. Stars with "intermediate" kinematics (P-1 < 0.7, P-2 < 0.7) do not all populate the region of the [O/Fe]-[Fe/H] plane intermediate between the mean thin-disk and thick-disk trends, but their distribution is not necessarily bimodal. Halo stars (P-3 > 0.5) show a large star-to-star scatter in [O/Fe]-[Fe/H], but most of it is due to stars with Galactocentric rotational velocity V < -200 km s(-1); halo stars with V > -200 km s(-1) follow an [O/Fe]-[Fe/H] relation with almost no star-to-star scatter. Early mergers with satellite galaxies explain most of our observations, but the significant fraction of disk stars with "ambiguous" kinematics and abundances suggests that scattering by molecular clouds and radial migration have both played an important role in determining the kinematic and chemical properties of solar neighborhood stars.
    Department
    McDonald Observatory
    Subject
    galaxy: disk
    galaxy: evolution
    galaxy: formation
    stars: abundances
    stars: atmospheres
    stars: fundamental parameters
    metal-poor stars
    geneva-copenhagen survey
    digital sky survey
    solar-type stars
    milky-way disk
    neutral hydrogen collisions
    effective
    temperature scale
    stellar angular diameters
    dark-matter universe
    infrared flux method
    astronomy & astrophysics
    URI
    http://hdl.handle.net/2152/34757
    Citation
    Ram�rez, I., C. Allende Prieto, and D. L. Lambert. "Oxygen Abundances in Nearby FGK Stars and the Galactic Chemical Evolution of the Local Disk and Halo." The Astrophysical Journal, Vol. 764, No. 1 (Feb., 2013): 78.
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