OH IR STARS - NEAR-INFRARED PHOTOMETRY, AND DISCUSSION OF THE MIRA-OH/IR SEQUENCE/

This paper presents JHKL'M photometry of a new sample of OH/IR stars. These data are merged with similar observations collected in the liter ature in order to constitute a data base of near-infrared photometry f or 400 OH/IR stars. After removing from this sample the objects that a re unlikely to be AGE stars, we obtain a sequence of average OH/IR sta rs with increasing values of the colour index K-L'. A simple model of a star surrounded by a circumstellar shell is constructed in order to derive basic parameters such as luminosity, radius, stellar temperatur e, optical depth of the dust shell and mass loss rate. These parameter s are found to vary smoothly along the sequence of OH/IR stars, and th e K-L' colour is shown to describe almost completely the basic physica l parameters of an OH/IR star. The metallicity affects the OH-peak sep aration, but does not play an important role in the definition of the other properties.