Possible evidence for metal accretion onto the surfaces of metal-poor main-sequence stars

Kohei Hattori, Yuzuru Yoshii, Timothy C. Beers, Daniela Carollo, Young Sun Lee

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    The entire evolution of the Milky Way, including its mass-assembly and star-formation history, is imprinted onto the chemo-dynamical distribution function of its member stars, f(x, v, [X/H]), in the multi-dimensional phase space spanned by position, velocity, and elemental abundance ratios. In particular, the chemo-dynamical distribution functions for low-mass stars (e.g., G- or K-type dwarfs) are precious tracers of the earliest stages of the Milky Way's formation, since their main-sequence lifetimes approach or exceed the age of the universe. A basic tenet of essentially all previous analyses is that the stellar metallicity, usually parameterized as [Fe/H], is conserved over time for main-sequence stars (at least those that have not been polluted due to mass transfer from binary companions). If this holds true, any correlations between metallicity and kinematics for long-lived main-sequence stars of different masses, effective temperatures, or spectral types must strictly be the same, since they reflect the same mass-assembly and star-formation histories. By analyzing a sample of nearby metal-poor halo and thick-disk stars on the main sequence, taken from Data Release 8 of the Sloan Digital Sky Survey, we find that the median metallicity of G-type dwarfs is systematically higher (by about 0.2 dex) than that of K-type dwarfs having the same median rotational velocity about the Galactic center. If it can be confirmed, this finding may invalidate the long-accepted assumption that the atmospheric metallicities of long-lived stars are conserved over time.

    Original languageEnglish
    Article number153
    Pages (from-to)1-11
    Number of pages11
    JournalAstrophysical Journal
    Issue number2
    Publication statusPublished - 1 Apr 2014

    Bibliographical note

    Copyright 2014 The American Astronomical Society. First published in the Astrophysical journal, 784(2), 153, 2014, published by IOP Publishing. The original publication is available at http://www.doi.org/10.1088/0004-637X/784/2/153. 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: evolution
    • Galaxy: formation
    • Galaxy: halo
    • Galaxy: kinematics and dynamics
    • stars: abundances


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