Protostars and Planets VI, Heidelberg, July 15-20, 2013
Near-infrared Metallicities, Radial Velocities and Spectral Types for 447 Nearby M Dwarfs
Newton, Elisabeth (Harvard-Smithsonian Center for Astrophysics)
We present metallicities, radial velocities and near-infrared spectral types for 447 M dwarfs using moderate resolution (R~2000) near-infrared (NIR) spectra obtained with IRTF/SpeX. These M dwarfs are primarily targets of the MEarth Survey, a transiting planet survey searching for super Earths around mid-to-late M dwarfs within 33pc. We present NIR spectral types for each star and new spectral templates for IRTF in the Y , J, H and K-bands, created using M dwarfs with near-solar metallicities. We created two spectroscopic distance calibrations that use NIR spectral type or an index based on the curvature of the K-band continuum. Our distance calibration has a scatter of 14%. We searched 27 NIR spectral lines and 10 spectral indices for metallicity sensitive features, taking into account correlated noise in our estimates of the errors on these parameters. We calibrated our relation using 36 M dwarfs in common proper pairs with an F, G or K-type star of known metallicity. We validated the physical association of these pairs using proper motions, radial velocities and spectroscopic distance estimates. Our resulting metallicity calibration uses the sodium doublet at 2.2 microns as the sole indicator for metallicity. It has an accuracy of 0.12 dex inferred from the scatter between the metallicities of the primaries and the estimated metallicities of the secondaries. Our relation is valid for NIR spectral types from M1V-M5V and for −1.0 < [Fe/H] < +0.35 dex. We present a new color-color metallicity relation using J - H and J - K colors that directly relates two observables: the distance from the M dwarf main sequence and equivalent width of the sodium line at 2.2 microns. We measured radial velocities by modeling telluric features to determine the absolute wavelength calibration, and used M dwarf binaries, observations at different epochs, and comparison to precisely measured radial velocities to demonstrate 4 km/s accuracy.
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