We report progress in the calibration of a method to determine cool dwarf star metallicities using molecular band strength indices .
The molecular band index to metallicity relation can be calibrated using chemical abundances calculated from atomic line equivalent width measurements in high resolution spectra .
Building on previous work , we have measured Fe and Ti abundances in 32 additional M and K dwarf stars to extend the range of temperature and metallicity covered .
A test of our analysis method using warm star – cool star binaries shows we can calculate reliable abundances for stars warmer than 3500 K. We have used abundance measurements for warmer binary or cluster companions to estimate abundances in 6 additional cool dwarfs .
Adding stars measured in our previous work and others from the literature provides 76 stars with Fe abundance and CaH2 and TiO5 index measurements .
The CaH2 molecular index is directly correlated with temperature .
TiO5 depends on temperature and metallicity .
Metallicity can be estimated to within \pm 0.3 dex within the bounds of our calibration , which extends from roughly [ Fe / H ] = +0.05 to - 1.0 with a limited extension to - 1.5 .