1992JAVSO..21...42W

A photometric system consisting of three near-infrared interference filters and designed for studies of red variable stars is described. It represents a simplification of the writer's eight-color system of classification photometry and is intended for use with small telescopes and inexpensive instrumentation. The three filters measure an infrared magnitude, a color index, and an index of TiO band strength, which indicates the spectral type. Measurements on this system should provide a valuable supplement to the visual light curves of red variable stars. A set of standard stars is given which will enable observers to reduce their measurements to a system of absolute fluxes. A procedure is described for deriving an index of TiO strength from the data and converting it to spectral type.