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The M dwarf problem in the Galaxy

Authors

  • Vincent M. Woolf,

    Corresponding author
    1. Department of Physics, University of Nebraska at Omaha, 6001 Dodge Street, Omaha, NE 68182, USA
      E-mail: vwoolf@unomaha.edu (VMW); aawest@bu.edu (AAW)
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  • Andrew A. West

    Corresponding author
    1. Department of Astronomy, Boston University, 725 Commonwealth Avenue, Boston, MA 02215, USA
      E-mail: vwoolf@unomaha.edu (VMW); aawest@bu.edu (AAW)
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E-mail: vwoolf@unomaha.edu (VMW); aawest@bu.edu (AAW)

ABSTRACT

We present evidence that there is an M dwarf problem similar to the previously identified G dwarf and K dwarf problems: the number of low-metallicity M dwarfs is not sufficient to match simple closed-box models of local Galactic chemical evolution. We estimated the metallicity of 4141 M dwarf stars with spectra from the Sloan Digital Sky Survey (SDSS) using a molecular band strength versus metallicity calibration developed using high resolution spectra of nearby M dwarfs. Using a sample of M dwarfs with measured magnitudes, parallaxes and metallicities, we derived a relation that describes the absolute magnitude variation as a function of metallicity. When we examined the metallicity distribution of SDSS stars, after correcting for the different volumes sampled by the magnitude-limited survey, we found that there is an M dwarf problem, with the number of M dwarfs at [Fe/H] ∼−0.5 less than 1 per cent the number at [Fe/H] = 0, where a Simple model of Galactic chemical evolution predicts a more gradual drop in star numbers with decreasing metallicity.

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