M-Dwarf Metallicities With K-band Spectra: Testing Calibrations With Observations of 133 Solar Neighborhood M-Dwarfs

Details M-Dwarf Metallicities With K-band Spectra: Testing Calibrations With Observations of 133 Solar Neighborhood M-Dwarfs M-Dwarf Metallicities With K-band Spectra: Testing Calibrations With Observations of 133 Solar Neighborhood M-Dwarfs

Jan 2012

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2012aas...21933003d&link_type=abstract

American Astronomical Society, AAS Meeting #219, #330.03

Astronomy and Astrophysics

Astronomy

Scientific paper

Contrary to their dimness, M-dwarf stars hold significant promise for illuminating the processes that govern the formation and evolution of stars, planets, and the Milky Way. Calibrating the fundamental parameters of M-dwarfs, however, is a difficult challenge from both an observational and theoretical perspective. In particular, the determination of their metallicities has proved to be extremely problematic. To address this problem, we obtained K-band spectra for 133 nearby (d<33 parsecs) M-dwarfs, including 18 M-dwarfs with FGK companions, 11 M-dwarf planet hosts, more than 2/3 of the M-dwarfs in the Northern 8pc sample, and several M-dwarfs from the LSPM catalog. From these spectra, we measured equivalent widths of the Ca and Na lines, and a spectral index quantifying the absorption due to H2O opacity. We used the strength of the Na, Ca and H2O features of 18 M-dwarfs with reliable metallicity estimates from FGK companions to construct an empirical [Fe/H] indicator applicable for M dwarfs with near-solar metallicities (-0.69<[Fe/H]<+0.31,sigma=0.141 dex). For the first time, we derive an expression for an M-dwarf's overall metallicity [M/H]; quantitative comparisons to model atmospheres, which are benchmarked according to overall metallicity, provide a qualitative validation of our approach, but also demonstrate an overall offset between the atomic line strengths predicted by models as compared to actual observations. Our metallicity estimates reproduce expected correlations between metallicity and Galactic space motions and Hα emission line strengths, as well as returning statistically identical metallicities for M-dwarf companions within a shorted multiple system. Finally, we provide a list with promising M-dwarfs targets for planet searches in the Solar Neighborhood based on their metallicity, Hα emission, and rotation.

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