We describe a method for accurately determining M dwarf metallicities with spectral synthesis based on abundance analyses of visual binary stars .
We obtained high resolution , high signal-to-noise spectra of each component of five visual binary pairs at McDonald Observatory .
The spectral types of the components range from F7 to K3 V for the primaries and M0.5 to M3.5 V for the secondaries .
We have determined the metallicities of the primaries differentially with respect to the Sun by fitting synthetic spectra to Fe i line profiles in the observed spectra .
In the course of our analysis of the M dwarf secondaries we have made significant improvements to the PHOENIX cool-star model atmospheres and the spectrum analysis code MOOG .
Our analysis yields a RMS deviation of 0.11 dex in metallicity values between the binary pairs .
We estimate the uncertainties in the derived stellar parameters for the M dwarfs to be 48 K , 0.10 dex , 0.12 dex , 0.15 km s ^ { -1 } , and 0.20 km s ^ { -1 } for T _ { eff } , log g , [ M/H ] , \xi , and \eta respectively .
Accurate stellar evolutionary models are needed to progress further in the analysis of cool-star spectra ; the new model atmospheres warrant recalculation of the evolutionary models .