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The ability to perform detailed chemical analysis of Sun-like F-, G-, andK-type stars is a powerful tool with many applications including studying thechemical evolution of the Galaxy and constraining planet formation theories.Unfortunately, complications in modeling cooler stellar atmospheres hinderssimilar analysis of M-dwarf stars. Empirically-calibrated methods to measure Mdwarf metallicity from moderate-resolution spectra are currently limited tomeasuring overall metallicity and rely on astrophysical abundance correlationsin stellar populations. We present a new, empirical calibration of synthetic Mdwarf spectra that can be used to infer effective temperature, Fe abundance,and Ti abundance. We obtained high-resolution (R~25,000), Y-band (~1 micron)spectra of 29 M dwarfs with NIRSPEC on Keck II. Using the PHOENIX stellaratmosphere modeling code (version 15.5), we generated a grid of syntheticspectra covering a range of temperatures, metallicities, andalpha-enhancements. From our observed and synthetic spectra, we measured theequivalent widths of multiple Fe I and Ti I lines and a temperature-sensitiveindex based on the FeH bandhead. We used abundances measured fromwidely-separated solar-type companions to empirically calibrate transformationsto the observed indices and equivalent widths that force agreement with themodels. Our calibration achieves precisions in Teff, [Fe/H], and [Ti/Fe] of 60K, 0.1 dex, and 0.05 dex, respectively and is calibrated for 3200 K < Teff <4100 K, -0.7 < [Fe/H] < +0.3, and -0.05 < [Ti/Fe] < +0.3. This work is a steptoward detailed chemical analysis of M dwarfs at a similar precision achievedfor FGK stars.

A physically motivated and empirically calibrated method to measure effective temperature, metallicity, and Ti abundance of M dwarfs