The ability to perform detailed chemical analysis of Sun-like F- , G- , and K-type stars is a powerful tool with many applications including studying the chemical evolution of the Galaxy and constraining planet formation theories .
Unfortunately , complications in modeling cooler stellar atmospheres hinders similar analysis of M-dwarf stars .
Empirically-calibrated methods to measure M dwarf metallicity from moderate-resolution spectra are currently limited to measuring overall metallicity and rely on astrophysical abundance correlations in stellar populations .
We present a new , empirical calibration of synthetic M dwarf spectra that can be used to infer effective temperature , Fe abundance , and Ti abundance .
We obtained high-resolution ( R \sim 25,000 ) , Y-band ( \sim 1 \micron ) spectra of 29 M dwarfs with NIRSPEC on Keck II .
Using the PHOENIX stellar atmosphere modeling code ( version 15.5 ) , we generated a grid of synthetic spectra covering a range of temperatures , metallicities , and alpha-enhancements .
From our observed and synthetic spectra , we measured the equivalent widths of multiple \ion Fe1 and \ion Ti1 lines and a temperature-sensitive index based on the FeH bandhead .
We used abundances measured from widely-separated solar-type companions to empirically calibrate transformations to the observed indices and equivalent widths that force agreement with the models .
Our calibration achieves precisions in T _ { \mathrm { eff } } , [ Fe/H ] , and [ Ti/Fe ] of 60 K , 0.1 dex , and 0.05 dex , respectively and is calibrated for 3200 K < T _ { \mathrm { eff } } < 4100 K , -0.7 < [ Fe/H ] < +0.3 , and - 0.05 < [ Ti/Fe ] < +0.3 .
This work is a step toward detailed chemical analysis of M dwarfs at a similar precision achieved for FGK stars .