Abstract
Usin gboth measured values and model atmospheres, the equivalent widths of the Na D lines of hypothetical late type main sequence binaries are calculated. Enhancements in the D lines of 90% over the value for a single star whose B - V color is the same as the composite B - V are possible. It is suggested that this effect may be used to identify binaries in galactic clusters, in particular those binaries whose components differ by more than 3 mag in brightness.
