continuum veiling. In this case line ratio diagnostics are to be preferred, since absorption features will appear shallower in the presence of continuum excess but line ratios will be preserved as long as the excess is not strongly wavelength dependent. We have identified one diagnostic based on line ratios which can be used to evaluate both temperature and luminosity for stars from K3-M5 in the presence of continuum veiling. This two–dimensional spectral index is defined as:

$$\frac{EW[OH5920]}{EW[Mg6345]} \ vs. 
\ \frac{EW[CO6018+CO6170]}{EW[Mg6345]}$$

where EW is the equivalent width in cm$^{-1}$ for the indices identified in Table \[ftshband\] and listed in Tables \[ftshewsup\]– \[ftshewdw\]. The temperature and luminosity dependence of this diagnostic is illustrated in Figure \[fig8\]. In this diagnostic, the ratio of the OH5920 to Mg6345 indices is temperature sensitive, with distinct temperature dependences for dwarfs and giants. Specifically we find

$$T_{eff} (V) = 4640 \pm 250 - (2610 \pm 110) \frac{EW[OH5920]}{EW[Mg6345]}$$

and

$$T_{eff} (III) = 5100 \pm 180 - (2730 \pm 80)\times \frac{EW[OH5920]}{EW[Mg6345]}$$

The comparison of this temperature sensitive ratio with the sum of the two $^{12}$CO indices, also normalized to Mg6345, then provides an excellent means of identifying both the temperature and luminosity class of late–type stars. Formal errors 